Composition Vendor Newgen KnowledgeWorks (P) Ltd. PLoS One plos plosone PLOS One 1932-6203 Public Library of Science San Francisco, CA USA 10.1371/journal.pone.0335400 PONE-D-24-03764 Research Article Medicine and health sciencesSurgical and invasive medical proceduresPediatric surgery Medicine and health sciencesEpidemiologyPandemics Medicine and health sciencesSurgical and invasive medical procedures Medicine and health sciencesSurgical and invasive medical proceduresOtolaryngological procedures Medicine and health sciencesSurgical and invasive medical proceduresMusculoskeletal system proceduresOrthopedic surgery Medicine and health sciencesCritical care and emergency medicine Medicine and health sciencesMedical conditionsInfectious diseasesViral diseasesCOVID 19 Medicine and health sciencesPediatrics The Covid-19 pandemic in Sweden: Prolonged and unevenly distributed effects on the volume of pediatric anesthesia and surgery demonstrated by data from the Swedish Perioperative Register Swedish pediatric surgery and anesthesia during Covid-19 https://orcid.org/0009-0003-7299-5414 Melander Sixten Conceptualization Data curation Formal analysis Investigation Methodology Writing – original draft Writing – review & editing 1 * Enlund Gunnar Conceptualization Supervision Writing – review & editing 2 https://orcid.org/0000-0002-1998-5212 Engstrand Lilja Helene Conceptualization Supervision Writing – review & editing 3 Frykholm Peter Conceptualization Methodology Project administration Supervision Visualization Writing – review & editing 1 Department of Surgical Sciences, Section of Anaesthesiology and Intensive Care Medicine, Uppsala University, Uppsala, Sweden Department of Anaesthesia and Intensive Care, Uppsala University Hospital, Uppsala, Sweden Department of Women’s and Children’s Health, Karolinska Institutet, Stockholm, Sweden Vilhelmsson, Andreas Editor Lund University, SWEDEN * E-mail: sixten.melander@gmail.com

The authors have declared that no competing interests exist.

 29102025 2025 20 10 e0335400 122024 11102025 2025 Melander et al This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Background

In 2020, Covid-19 pushed Swedish health care to its limits regarding access to hospital beds and staffing. A previous investigation of the effects of the first wave of the pandemic in the spring of 2020 revealed a substantial reduction in elective pediatric surgery. The aim of the present study was to expand this analysis on a national and regional level during almost three years with Covid-19.

 Methods

For this retrospective cohort study, routine data from all procedures in patients <16 years of age in 2019–2022 were extracted from the Swedish Perioperative Register. Data were analyzed according to level of care, type of surgery, procedure code and emergency or elective surgery.

 Results

During 2020–2022, the number of surgeries registered was 19,944 fewer than expected as compared to pre-pandemic levels, i.e., a reduction of about 12%. Elective surgery showed a total reduction of 17% while emergency surgery was unaffected. The most dramatic decrease was found in county hospitals where elective surgery was reduced by 28% and the largest effect was found in Ear, Nose, and Throat/oral surgery (−34%). Patient age at the time of surgery did not show any notable differences in total, except for grommets insertion in 2021 and adenoidectomy in 2021 and 2022 compared to 2019.

 Conclusion

The Covid-19 pandemic affected the number of surgical procedures in children for more than two years. Future studies of the long-term effects of the large number of canceled operations are warranted.

 The author(s) received no specific funding for this work. Data Availability The Swedish Ethical Review Authority restricts sharing of data since they contain potentially sensitive information. The data is managed by the Swedish Perioperative Register at the Uppsala Clinical Research Centre. Contact person for data requests is Beata Pajak UCR | Uppsala Clinical Research Center Uppsala Science Park, Hubben Dag Hammarskjölds väg 38 751 85 UPPSALA SWEDEN beata.pajak@ucr.uu.se. Introduction

During the Covid-19 pandemic, the health care service had to redirect its focus and adjust to expand the capacity of intensive care units (ICU) [1]. These adjustments affected different facilities and disciplines according to a report from the National Board of Health and Welfare (NBHW) [2]. From both anesthesiological and surgical perspectives, substantial changes have been reported, such as canceled operations, creation of temporary Covid-related wards, and anesthetic personnel relocated to the ICU [3].

According to another report from the NBHW [4,5], there have been four major waves of Covid-19 in Sweden. The first wave was defined to encompass March – September 2020, the second wave October 2020 – January 2021, the third wave February – June 2021 and the fourth wave July 2021 – March 2022 respectively.

Children are less likely to develop severe Covid-19 disease than adults [6]. The pandemic could still directly or indirectly have had significant effects on pediatric health care services. Cancellation of surgery leading to an increased age at surgery is one example, and it could potentially have affected children’s health regarding both short and long-term aspects. We have previously reported that pediatric elective procedures were reduced by more than 50% during the first wave of the pandemic in 2020 [7]. There is a paucity of data concerning the continued effects on pediatric hospitalization and surgery. Therefore, we decided to investigate patterns in the reduction of pediatric procedures on national and regional levels during almost three years with Covid-19. We also aimed to explore the possibility of postponed surgery leading to children being operated at an older age. We hypothesized that the number of cases would continue to be reduced in spite of less hospitalization due to Covid-19 during the studied period.

 Methods

This is a retrospective cohort study based on data extracted from the Swedish Perioperative Register (SPOR). SPOR does not take responsibility for the methods, analysis and results, and the views expressed in this study may not necessarily reflect those of SPOR. Informed consent was waived by the Swedish Ethics Review Authority (permission no 2020−01909). Data was accessed on March 1st 2023. The dataset from SPOR used in this study did not contain complete ID information for individual patients. To be precise, we had information regarding the age at the time of surgery expressed in years and months but not days. Patient name or other identification markers were not available to our research group. The report contained all procedures registered by SPOR from January 1st 2019 to December 31st 2022. The register includes all procedures performed with anesthesia services involved, i.e., general anesthesia but also diagnostic procedures or treatments with sedation.

Data sources

SPOR was initiated by the Swedish Society for Anaesthesia and Intensive Care, set up in 2011, and started including data in 2011. All data is managed by Uppsala Clinical Research Centre, which runs many of the largest nationwide quality registers in Sweden. The purpose of SPOR is to provide data for national and local quality assurance projects and research. It is not used for billing purposes. Data are uploaded daily through smooth integration with local surgery planning and billing systems. A process for validation of data is ongoing since several years.

The Swedish Intensive Care Register (SIR) has a similar design and was initiated in 2001 by the same professional organization. The purpose of SIR is to promote and develop quality in Swedish intensive care. Both the above registers have Certification Level 1 and publish open access reports continuously on their respective websites.

 Inclusion and exclusion criteria

Only children <16 years of age at the date of surgery were included, and centers that had not started reporting January 1st 2019 or stopped reporting to SPOR after 2019 were excluded, to enable comparisons with pre-pandemic conditions. We decided early in the planning of the study to only include centers that reported data all four years. All hospitals connected to SPOR upload their data automatically to the register monthly. The uploading process has been validated for all data fields used in this study [8]. Data consist of patient ID, type of surgery, diagnoses, time stamps during the perioperative process (from the decision to operate to the time of discharge from the postoperative recovery area) as well as quality measures.

The year 2019 was defined as baseline for analyses of changes in caseload. The absolute number of cases as well as percentage changes relative to the corresponding baseline periods were reported.

 Outcomes

The primary outcome was reductions in total number of procedures during the pandemic years of 2020, 2021 and 2022 compared to corresponding pre-pandemic numbers, i.e., during 2019. Secondary outcomes were differences in caseload reduction regarding 1) level of care (university, district, and county hospital, as indicated in SPOR; university hospitals are tertiary centers with 24–7 services for most pediatric surgical and medical services, district hospitals have no separate pediatric anesthesia or surgery but capacity to treat children 24–7, county hospitals have only core medical and surgical services and the term smaller units is reserved for private clinics typically focused on elective surgery in a single speciality), 2) surgical specialty according to the national surgical procedure code system KVA-97 [9], 3) emergency vs elective surgery, and 4) age at the time of surgery. For the primary outcome, we determined the weekly caseload and compared to the corresponding week in 2019 to study the evolution of the effects of the pandemic over time. To put these changes into context of the fluctuating intensity of the pandemic we retrieved the number of new admissions to all Swedish Intensive Care Units (ICU) from the Swedish ICU Register [10]. Furthermore, a sub-analysis of the changes during the four different waves of the pandemic was performed, comparing them to baseline numbers of 2019 and displaying differences in number of procedures per day including separate data on emergency and elective procedures.

Finally, out of a total of 3,276 different registered procedures we analyzed mean age at the time of surgery for the 20 most common procedures in 2019 for each of the different years of the study period, to provide more detail and probe for potentially delayed scheduling. Regional distribution as well as changes in waiting times during the pandemic were investigated.

 Confounders

Possible confounders are, e.g., demographic changes such as increasing immigration and variations in nativity, the increasing cost of health care both before and during the pandemic, and possible changes in political policy. These were not accounted for.

 Statistical methods

The dataset is a convenience sample based on data available at the time of study planning. Differences are displayed as absolute and percentage reductions. Poisson regression was used to analyze the main categories during the different years adjusted for risk population based on the population <16 years of age in Sweden during each year using data from Statistics Sweden [11]. Student’s t-test was used to investigate changes in patient age at surgery; differences displayed with 95% confidence intervals. A p-value of less than 0.05 was considered statistically significant. Data was managed and analyzed using Microsoft Excel (Version 2210 Build 16.0.15726.20188) and R version 4.1.1.

 Results

The number of procedures was 214,964 reported from 82 centers (14 university hospitals, 20 county hospitals, 45 district hospitals and 3 smaller units). Due to nonreporting during any of the four included years we excluded 2 county hospitals (n = 3,750), 5 district hospitals (n = 394) and 2 smaller units (n = 2,368). The final number of analyzed procedures was thus 208,452. A flowchart of the process is displayed in Fig 1.

10.1371/journal.pone.0335400.g001Cohort flow chart.

The number of procedures enrolled, exclusions due to incomplete reporting during any of the four studied years and total number of procedures included for analysis.

The total number of procedures performed in 73 reporting hospitals was 57,099, 49,000, 49,091, and 53,262 procedures in 2019, 2020, 2021 and 2022 respectively (displayed in Table 1). The total reduction during the three pandemic years compared to 2019 as our baseline amounts to 19,944 fewer procedures than what would have been expected without the pandemic, a decrease of approximately 12%. The years 2020 and 2021 showed a similar total reduction of 14%, while 2022 showed a less pronounced reduction of 7%. In Fig. 2, weekly cases are displayed as percentages of the corresponding weeks in 2019, with the number of new ICU-admissions during these 7-day periods superimposed, using data from the Swedish ICU register [10]. The most dramatic reduction in caseload was found in the spring of 2020, with continued, albeit less marked, reductions during the years of 2020, 2021 and 2022 (Table 2). Throughout the pandemic, elective surgery was severely affected while emergency surgery was left largely unchanged. Thus, 40,670, 32,452 (- 20%), 32,123 (- 21%), and 36,960 (- 11%) elective procedures were registered during 2019, 2020, 2021 and 2022 respectively (Table 1). The corresponding numbers for emergency surgery were 16,429, 16,548, 16,968 and 16,302.

10.1371/journal.pone.0335400.t001Analyses of number of procedures in hospital categories and main specialties.
2019 2020 2021 2022 Total Difference
Total 57,099 49,000 (86%,  < 0.001) 49,091 (86%, < 0.001) 53,262 (93%. < 0.001) −19,944 (−12%)
Total Emergency 16,429 16,548 (101%, 0.640) 16,968 (103%, 0.013) 16,302 (99%, 0.459) 531 (1%)
Elective 40,670 32,452 (80%, < 0.001) 32,123 (79%, < 0.001) 36,960 (91%, < 0.001) −20,475 (−17%)
University Emergency 9,376 9,446 (101%, 0.716) 9,789 (104%, 0.008) 9,249 (99%, 0.337) 356 (1%)
Hospitals Elective 20,907 18,636 (89%, < 0.001) 18,551 (89%, < 0.001) 21,137 (101%, 0.283) −4,397 (−7%)
County Emergency 5,506 5,590 (102%, 0.494) 5,648(103%, 0.280) 5,524 (95%. 0.886) 244 (1%)
Hospitals Elective 13,306 9,229 (69%, < 0.001) 8,971 (67%, < 0.001) 10,511 (79%, < 0.001) −11,207 (−28%)
District Emergency 1,547 1,512 (98%, 0.492) 1,531 (99%, 0.678) 1,529 (99%, 0.746) −69 (−1%)
Hospitals Elective 6,004 4,264 (71%, < 0.001) 4,153 (69%, < 0.001) 4,799 (80%, < 0.001) −4,796 (−26%)
ENT/Oral Emergency 790 687 (−87%, 0.007) 698 (88%, 0.014) 830 (105%, 0.333) −155 (−7%)
surgery Elective 13,829 9,230 (67%, < 0.001) 7,884 (57%, < 0.001) 10,256 (74%, < 0.001) −14,117 (−34%)
General Emergency 3,019 3,156 (104%, 0.098) 3,260 (108%, 0.005) 2,948 (98%, 0.351) 307 (3%)
Surgery Elective 2,447 2,116 (86%, < 0.001) 2,025 (83%, < 0.001) 2,208 (90%, < 0.001) −992 (−14%)
Orthopedic Emergency 6,051 5,956 (98%, 0.329) 5,813 (96%, 0.014) 5,660 (94%, < 0.001) −724 (4%)
Surgery Elective 4,616 3,907 (85%, < 0.001) 4,204 (91%, < 0.001) 4,614 (100%, 0.967) −1,123 (−8%)
Urological Emergency 724 777 (107%, 0.188) 828 (114%, 0.011) 826 (114%, 0.010) 259 (12%)
Surgery Elective 3,241 2,627 (81%, < 0.001) 2,634 (81%, < 0.001) 2,723 (84%, < 0.001) −1,739 (−18%)
Inhabitants of Sweden 1,951,765 1,955,716 1,961,414 1,952,650
<16 years of age**

*ENT – Ear, Nose and Throat.

**Information gathered from Statistics Sweden SCB September 8th 2023.

The total number of procedures during 2019–2022 are displayed as emergency and elective categories. Displayed in brackets are firstly their percentage ratios compared to the corresponding numbers in 2019, secondly p-values calculated through rate-ratio comparisons of the number of procedures during the different years, using a Poisson regression, adjusted for the Swedish population at risk during that specific year, using data from Statistics Sweden [11]. Total Difference signifies the sum of difference during the whole pandemic period from start of 2020 to the end of 2022; mean percentage difference per year is displayed in brackets.

 10.1371/journal.pone.0335400.g002Cases and ICU admissions throughout the pandemic.

Weekly total (black), elective (blue) and emergency (yellow) cases displayed as percentages of the corresponding weeks in 2019. The number of new ICU-admissions during these 7-day periods are superimposed using data from the Swedish ICU register [10]. New Year’s Eve was not included in the 7-day period and February 29th of 2020 was excluded. The official pandemic waves 1 - 4 and year transitions are marked on the x-axis.

In the rate-ratio analyses, statistically significant changes were found in elective surgery for all specialties and all hospital categories in 2020 and 2021 (last six columns in Table 1). In 2022, significant reductions in elective surgery were found in district and county hospitals but not in university hospitals. Regarding emergency surgery, statistically significant reductions were found for ENT (Ear, nose and throat)/oral surgery in 2020, and in 2021 for university hospitals. University hospitals (n = 14) showed the least marked reduction of elective surgery with a total deficit of 4,397 (7%) over the 3 year period, while county hospitals (n = 18) showed the largest reduction with 11,207 (28%) fewer procedures. District hospitals (n = 40) produced 4,796 (26%) fewer procedures.

Four major groups of surgical specialties were analyzed: ENT/oral surgery, general surgery, orthopedic surgery and urological surgery. As far as elective surgery goes, all specialties showed a reduction ranging from 34% in ENT/oral surgery to 8% in orthopedic surgery. Emergency surgery was reduced by 7% for ENT/oral surgery and by 4% for orthopedic surgery, while general and urological surgery actually increased output by 3% and 12% respectively. In total numbers ENT/oral surgery was most severely affected, a reduction of 14,272 procedures. The corresponding numbers were 1,847 for orthopedic surgery, 1,480 for urological surgery and 685 for general surgery.

10.1371/journal.pone.0335400.t002Number of procedures during the four waves.
Wave 1 (March-September 2020)
Emergency Elective Total
2019 10,403 22,058 32,461
Wave 1 10,450 14,811 25,261
Difference 47 −7,247 −7,200
Difference (%) 0.45% −32.85% −22.18%
Difference/day 0.22 −33.86 −33.64
Wave 2 (October 2020 – January 2021)
Emergency Elective Total
2019 4,925 15,165 20,090
Wave 2 4,924 12,325 17,249
Difference −1 −2,840 −2.841
Diff (%) −0.02% −18.73% −14.14%
Difference/day −0.01 −23.09 −23.10
Wave 3 (February – June 2021)
Emergency Elective Total
2019 6,946 17,871 24,817
Wave 3 7,159 13,924 21,083
Difference 213 −3,947 −3,734
Diff (%) 3.07% −22.09% −15.05%
Difference/day 1.41 −26.14 −24.73
Wave 4 (July 2021 – March 2022)
Emergency Elective Total
2019 11,840 30,177 42,017
Wave 4 12,146 26,094 38,240
Difference 306 163 −4,083 −3,777
Difference (%) 2.58% −13.53% −8.99%
Difference/day 1.12 −14.90 −13.78

Comparison of the four different waves as defined by NBHW [4,5], displaying Emergency, Elective and Total procedures during the different waves and during corresponding dates in 2019. Also displayed is the total difference and percentage difference between number of procedures compared to corresponding dates in 2019, as well as the difference per day in procedures. Wave 1 lasted for 214 days, wave 2 for 123 days, wave 3 for 151 days and Wave 4 for 274 days.

Waiting times for adenoidectomy during 2022 are shown for the different regions of Sweden in Fig 3. Waiting times varied between the different regions, with some reporting waiting times of three years or more.

10.1371/journal.pone.0335400.g003Distribution of waiting time for adenoidectomy during the pandemic.

Distribution of waiting times for adenoidectomy (EMB30) in the regions of Sweden during 2022. Waiting times were extracted from SPOR by calculating the difference between the time stamp for “Start of surgery” minus the time stamp for “Decision to operate”.

There was a small increase in total mean age at surgery during the study period, of approximately two months when comparing 2019 and 2022 (Table 3). Of the 20 most common procedures, we report a statistically significant increase in age from 4.72 (4.57–4.87) years in 2019 to 5.2 (4.94–5.49) in 2021 at the time of grommets insertion, a difference of 6.53 months. Similarly, age at tonsillectomy was 8.27 (8.0–8.57) years in 2019 vs 9.21 (8.76–9.66) in 2021 and 9.46 (9.0–9.91), i.e., mean increases of 11.3 and 14.3 months respectively.

10.1371/journal.pone.0335400.t003The 20 most common procedures.
Year 2019 2020 2021 2022 Total
Operation n Mean Age n Mean Age n Mean Age n Mean Age n Mean Age
Adenoidectomy 3,079 5.24 (5.12-5.35) 2,001 5.23 (5.09-5.37) 1,731 5.15 (4.99-5.30) 2,505 4.83 (4.71-4.95) 9,316 5.11 (5.04-5.17)
Diagnostic exam* 1,798 5.14 (4.96-5.32) 1,722 4.94 (4.76-5.12) 1,828 5.13 (4.95-5.30) 2,201 5.38 (5.21-5.55) 7,549 5.16 (5.07-5.25)
Gastroscopy 1,699 9.29 (9.09-9.49) 1,395 9.71 (9.49-9.92) 1,588 9.34 (9.14-9.55) 1,628 9.17 (8.96-9.37) 6,310 9.37 (9.26-9.47)
Intracapsular destruction of tonsil 2,334 4.76 (4.66-4.86) 1,471 4.57 (4.45-4.70) 1,042 4.69 (4.53-4.86) 1,173 4.58 (4.43-4.73) 6,020 4.67 (4.60-4.73)
Laparoscopic appendectomy 1,306 10.9 (10.8-11.1) 1,557 10.9 (10.7-11.0) 1,588 10.9 (10.7-11.0) 1,501 10.8 (10.7-11.0) 5,952 10.9 (10.8-11.0)
MRI Brain 1,224 4.83 (4.61-5.04) 1,268 4.61 (4.39-4.82) 1,386 4.29 (4.11-4.48) 1,367 4.52 (4.32-4.71) 5,245 4.55 (4.45-4.65)
Lumbar puncture 1,475 6.64 (6.43-6.85) 1,267 6.59 (6.36-6.82) 1,253 6.04 (5.81-6.28) 1,053 5.84 (5.60-6.08) 5,048 6.31 (6.20-6.43)
Tooth extraction 1,548 7.19 (7.03-7.35) 1,107 6.97 (6.78-7.16) 1,083 7.15 (6.97-7.33) 1,309 7.23 (7.05-7.40) 5,047 7.14 (7.05-7.23)
Forearm/elbow X,** closed reduction 1,209 8.34 (8.14-8.54) 1,165 8.32 (8.12-8.53) 979 8.42 (8.20-8.65) 1,067 8.42 (8.20-8.63) 4,420 8.37 (8.27−8,48)
Grommets 1,645 4.72 (4.57-4.87) 856 4.93 (4.70-5.15) 517 5.21 (4.94-5.49) 893 4.68 (4.48-4.88) 3,911 4.82 (4.72-4.92)
Laparoscopic Excision inguinal hernia 1,061 3.46 (3.26-3.67) 947 3.61 (3.39-3.83) 844 3.56 (3.33-3.79) 891 3.68 (3.46-3.91) 3,743 3.58 (3.47-3.68)
Operation for undescended or ectopic testis. 915 4.81 (4.56-5.06) 746 5.04 (4.76-5.32) 786 5.14 (4.88-5.41) 766 5.11 (4.83-5.39) 3,213 5.02 (4.88-5.15)
Osteosynthesis of forearm or elbowX** 683 8.39 (8.13-8.65) 697 8.06 (7.80-8.32) 664 8.62 (8.35-8.89) 674 8.39 (8.12-8.65) 2,718 8.37 (8.27-8.48)
Stereotactic intracranial radiation therapy 685 4.95 (4.74-5.14) 572 5.16 (4.99-5.34) 489 5.14 (4.88-5.41) 791 4.68 (4.53-4.84) 2,537 4.95 (4.85-5.05)
Removal of fracture fixation material Forearm/elbow X** 559 9.25 (8.96-9.53) 572 9.20 (8.93-9.48) 549 9.38 (9.10-9.67) 560 9.43 (9.15-9.70) 2,240 9.31 (9.17-9.45)
Tonsillectomy 829 8.27 (8.00-8.55) 508 8.85 (8.49-9.22) 363 9.21 (8.76-9.66) 358 9.46 (9.00-9.91) 2,058 8.79 (8.61-8.97)
Circumcision 641 8.84 (8.53-9.15) 468 8.99 (8.63-9.35) 460 9.04 (8.67-9.40) 488 8.84 (8.47-9.20) 2,057 8.92 (8.74-9.09)
Osteosynthesis of wrist or hand X** 444 10.9 (10.6-11.2) 480 10.4 (10.1-10.7) 515 10.4 (10.1-10.7) 513 11.2 (10.9-11.5) 1,952 10.7 (10.6-10.9)
Wrist or hand X** closed reduction 523 9.86 (9.56-10.2) 491 9.83 (9.53-10.1) 465 9.85 (9.56-10.2) 468 10.0 (9.72-10.3) 1,947 9.89 (9.74-10.0)
Adenotonsillectomy 703 5.05 (4.82-5.28) 493 4.88 (4.60-5.17) 339 4.63 (4.25-5.00) 351 4.42 (4.05-4.79) 1,886 4.81 (4.66-4.96)
Total 57,099 6.84 (6.80-6.88) 49,000 6.89 (6.83-6.95) 49,091 7.00 (6.94-7.06) 53,262 7.01 (6.95-7.07) 208,452 6.93(6.91-6.95)

*Diagnostic procedures under general anesthesia or sedation performed by anesthesiologists.

**X – fracture.

The 20 most common procedures during our study period, displayed yearly and with totals, showing number of operations (n), mean age at time of operation and 95% confidence intervals displayed in brackets.

 Discussion

This Swedish register-based study showed that over the course of three full years after the Covid-19 pandemic, the pediatric surgery volume was lower compared to the year before the pandemic. Total caseload remained below historical weekly averages during the entire pandemic, except for a few single weeks. The most dramatic decrease was found during the first wave in the spring of 2020, confirming previously published results [7].

Emergency vs elective surgery

Elective surgery was severely affected while there was no decline in emergency surgery. There are several plausible explanations for elective surgery cancellations during the pandemic. For example, patients or health care workers having symptoms of Covid-19, personnel relocation or simply postponement of non-urgent surgery to focus on the pandemic. In addition, recommendations for social distancing may have led to reductions in common pediatric respiratory illnesses [12–15] which could possibly have affected the number of procedures. One Dutch review reported that the Covid-19 pandemic caused significant decrease in pediatric admissions and emergency department (ED) utilization in both the Netherlands and the rest of the world [16]. Furthermore, a German study found that ED consultation during each phase of the pandemic was lower than in pre-pandemic conditions, with larger reductions displayed for less urgent patient consultations and younger patients [17]. This is in line with a British study from the beginning of the pandemic displaying large reductions in ED-visits with the most marked reductions reported in school-age children [18]. A US study found a 42% decline in ED visits during the early pandemic compared to 2019 and found that this reduction was especially pronounced for children and females [19]. Regarding surgical volume during the pandemic a cohort study from a large hospital in Massachusetts found a decline of 44,6% in the early weeks of the pandemic, with the largest differences being displayed in laryngeal, plastic, oral maxillofacial and general surgery while emergent/urgent surgery was less severely affected [20]. This is in line with our results showing more marked reductions in the elective category. There are large spikes in elective surgery in Fig 1 during the last two weeks of 2020, 2021 and 2022. These outliers may be artifacts, explained by the customary low rate of elective surgery during the Christmas season.

 ENT surgery most severely affected

Ear, nose and throat/oral surgery was the group most significantly affected. There could be several explanations for this. Firstly, ENT procedures in children can be postponed for months or even years without serious harm to the children. This is generally the case for, e.g., grommets insertion, tonsillectomy and adenoidectomy, all of which are on the list of the 20 most common procedures (Table 3). However, some children will suffer harm from the consequences of postponing both grommets insertion and tonsil surgery, respectively.

Tonsillectomy has two main indications: sleep-disordered breathing (SBD) and recurrent tonsillitis. In a meta-analysis, SDB was associated with later subsequent development of neurobehavioral deficits (pooled RR 3.24, 95%CI 1.25–8.41) [21]. Furthermore, it has been shown that children with SDB have higher antibiotic usage rates, more hospital visits and more healthcare visits due to upper respiratory infections [22]. The benefits of surgical treatment due to the latter indication are less clear. According to a Cochrane review from 2014, adenoid-/tonsillectomy leads to a reduction in the number of episodes of sore throat and days with sore throat in children in the first year after surgery compared to (initial) non-surgical treatment, although the size of effect of surgery was described as “modest” [23]. Secondly, aerosol-producing otolaryngologic procedures were identified as high-risk early in the pandemic due to the high viral load in the oropharyngeal cavity and adjacent structures, and otolaryngologists were among the first physician casualties [24]. This coupled with the fact that children are more prone to respiratory infections which can be hard to distinguish from a Covid-19 infection made surgical planning difficult and elective procedures in children with upper respiratory tract infections (even when Covid-19 was not the culprit) were therefore postponed at least 7 weeks during the pandemic [25].Thirdly, a large quantity of the surgeries are procedures on the tonsils, where infection is one indication for surgery and infections of the upper respiratory tract have been less common during the pandemic because of social distancing, as shown by the Swedish National Board of Health and Welfare and the Public Health Agency of Sweden [14,15].

 Potential costs and benefits of postponing surgery

Postponing surgery may be problematic for several reasons, such as advancement of illness or increased burden of disease. Especially relevant in children is a window of opportunity being lost, e.g., for cochlear implants, orchidopexy or hypospadias surgery. Fortunately, we found no convincing evidence of significantly higher age at surgery for the sum of the 20 most common procedures except for grommets and tonsillectomy (Table 3). The risk of postponing grommets in children is chronic and recurrent ear infections with fluid in the middle ear leading to hearing loss that in turn affects the child’s speech and language development [26]. In line with the discussion above about the consequences of postponing the common ENT procedures, surgery for undescended testis should ideally be performed before the age of 1 to avoid increased risk of infertility and malignancy, although the evidence for the latter is a contentious issue [27]. While the overall age at operation for, e.g., undescended or ectopic testis did not increase significantly, it is likely that many of these operations were postponed beyond the age of 12 months in some if not all centers.

However, potential positive effects have been suggested by Gelardi et al. who reported an improvement in symptomatology for children waiting for adenoidectomy, hinting at a reduced need for surgery during the pandemic [28]. Similarly, Marom et al. reported a reduced incidence in acute otitis media episodes during the pandemic, with high spontaneous resolution rates in children associated with the reduction in grommets insertion procedures [29].

 The uneven burdens of a backlog

Cancellations during the pandemic add burden to an already existing health care debt. This might be especially true for procedures with lower priority. This is illustrated in Fig 3, showing waiting times of several years for adenoidectomy in some regions. The regional differences are striking: the waiting times of > 1.5 years ranges from 0 to 51%, in a few regions reaching more than 3 years. We could speculate that the pandemic has aggravated regional issues with unequal access to health care. Moreover, university hospitals were less affected than the smaller district and county hospitals. This could be because of centralization of more complex pediatric cases to university hospitals, while district/county hospitals mainly deal with basic ENT surgery. For example, procedures on neonates and infants are mostly handled by university hospitals in Sweden, and university hospitals display a higher mortality than county and district hospitals [30]. These more complex cases could be less prone to cancellation or postponement.

Health care workers all over the world are still dealing with this post-pandemic backlog while at the same time having to recover from the stress of the pandemic and worker fatigue [31]. Burnout was a problem for healthcare workers even before the pandemic [32] and the increased workload and stress of the pandemic may have added new social and work-related factors that increase risk of burnout. These problems were aggravated in developing countries where vaccination programs had not yet reached the majority of the population. However, these challenges may trigger initiatives to increase workflow [33,34] and reduce late cancellation rates by more rigorous pre-operative screening protocols [12]. Jiang and Carvalho showed an increased OR-efficiency during the pandemic, with lower cancellation rates due to “no show” or “family refusal” [12]. They stipulated mandatory pre-operative Covid-tests causing increased nursing communications and education as a possible explanation. Future studies will be needed to understand the long-term consequences of three years of backlog of more than 10% of the annual number of procedures, possibly adding on to known issues of hospital staffing shortages causing staff relocations, external recruitments, added hours and lost hours due to illnesses, in Sweden during the pandemic [35].

 Strengths and limitations

The strength of the present study is that it provides data from a national perioperative database including almost all major Swedish hospitals with pediatric anesthesia. However, some important limitations are noted. The study is retrospective and it was not possible for us to adjust for all possible confounders such as changes in demographics, the increasing cost of health care, etc. This limits the ability to draw conclusions regarding cause-effect. Another limitation is that while presently (2025) SPOR covers 100% of Swedish government-run hospitals a few private clinics perform a small number of pediatric cases without reporting their data to SPOR. It is likely that the private clinics were at least as severely affected by the pandemic as government hospitals but their relative contribution to the results would be negligible since their estimated total caseload is a few percent of the total number of pediatric procedures in Sweden. Moreover, the single year of 2019 serves as baseline in the analysis of the volume for the three following years of the pandemic. The reason for using only 2019 as the baseline year was that this was the first year in which almost all Swedish Hospitals had joined the register. Ideally, we would have had access to complete baseline data from at least three years but since the register was still lacking data from several major centers, inclusion of data reported earlier than 2019 would have been less reliable. Theoretically, the production volume could have been unusually high during 2019, causing an incorrect analysis of reduced volume, but we have no reason to believe that this is the case.

Furthermore, we identified two small hospitals with a total caseload of < 1000 cases per year that stopped their reporting after 2021 and were therefore excluded. We have no information if they stopped reporting due to the pandemic per se or because of increased centralization or re-organization of patient flow during these years. An additional seven small hospitals were excluded since they joined SPOR after 2019 which precluded comparisons with baseline conditions before the pandemic. Finally, the pandemic was not fully contained within the study period, but our data indicates that caseload was returning to base-line numbers at the end of 2022.

 Conclusions

The Covid-19 pandemic affected the number of surgical procedures in children for more than two years. Future studies of the long-term effects of the large number of canceled operations are warranted.

 Supporting information Common pediatric surgeries during the years of the pandemic.

Yearly total number and quota compared to 2019 of five selected common pediatric surgeries in Sweden.

(JPG)

 Evolution of waiting time for adenoidectomy.

Monthly evolution of waiting time for adenoidectomy (EMB30) shown in days to surgery (blue = mean, gray = median). Waiting time is drawn from data in SPOR by calculating the difference between the time stamp for “Start of surgery” minus the time stamp for “Decision to operate”.

(TIF)

 Evolution of waiting time for surgeries on tonsils.

Monthly evolution of waiting time for surgeries on tonsils (EMB) shown in days to surgery (blue = mean, gray = median). Waiting time is drawn from data in SPOR by calculating the difference between the time stamp for “Start of surgery” minus the time stamp for “Decision to operate”.

(TIF)

 Evolution of waiting time for inguinal hernia surgery.

Monthly evolution of waiting time for inguinal hernia surgery (JAB) shown in days to surgery (blue = mean, gray = median). Waiting time is drawn from data in SPOR by calculating the difference between the time stamp for “Start of surgery” minus the time stamp for “Decision to operate”.

(TIF)

 Evolution of waiting time for gastrostomy.

Monthly evolution of waiting time for gastrostomy (JDB) shown in days to surgery (blue = mean, gray = median). Waiting time is drawn from data in SPOR by calculating the difference between the time stamp for “Start of surgery” minus the time stamp for “Decision to operate”.

(TIF)

 Evolution of waiting time for orchidopexy.

Monthly evolution of waiting time for orchidopexy (KFH) shown in days to surgery (blue = mean, gray = median). Waiting time is drawn from data in SPOR by calculating the difference between the time stamp for “Start of surgery” minus the time stamp for “Decision to operate”.

(TIF)

The authors would like to thank Fabian Söderdahl and Johan Bring at Statisticon AB for help with the statistical analysis.

 References Ludvigsson JF. How Sweden approached the COVID-19 pandemic: Summary and commentary on the National Commission Inquiry. Acta Paediatr. 2023;112(1):19–33. doi: 10.1111/apa.16535 36065136 Analys om coronapandemins effekter på vården [Internet]. Socialstyrelsen. [cited 2022 Dec 5]. Available from: https://www.socialstyrelsen.se/statistik-och-data/statistik/pandemins-effekter-pa-varden/analys-uppdamda-vardbehov-efter-pandemin/ Vera San Juan N, Clark SE, Camilleri M, Jeans JP, Monkhouse A, Chisnall G, et al. Training and redeployment of healthcare workers to intensive care units (ICUs) during the COVID-19 pandemic: a systematic review. BMJ Open. 2022;12(1):e050038. doi: 10.1136/bmjopen-2021-050038 34996785 Uppdrag att stödja regionernas hantering av uppdämda vårdbehov samt följa och analysera väntetider i hälso- och sjukvården. Regeringsbeslut 2020-06-25. Dnr S2020/05634/FS [cited 2022 Dec 5] Available from: https://www.regeringen.se/contentassets/67003d0bc0c54da68d5446c5de6dfb59/uppdrag-att-stodja-regionernas-hantering-av-uppdamda-vardbehov-web.pdf Regeringsuppdrag att stödja regionernas hantering av uppdämda vårdbehov samt följa och analysera väntetider i hälso- och sjukvården – Slutrapport mars. 2022. [Internet]. Socialstyrelsen. [cited 2025 Sept 1]. Available from: https://www.socialstyrelsen.se/contentassets/af10f61ee18245dbb1543cd1773002e3/2022-3-7798.pdf Nikolopoulou GB, Maltezou HC. COVID-19 in Children: Where do we Stand? Arch Med Res. 2022;53(1):1–8. doi: 10.1016/j.arcmed.2021.07.002 34311990 Melander S, Almström J, Enlund G, Frykholm P. The COVID-19 pandemic first wave in Sweden: A national registry study of the effects on pediatric anesthesia and surgery. Paediatr Anaesth. 2021;31(8):846–53. doi: 10.1111/pan.14203 33971054 Holmström B, Enlund G, Spetz P, Frostell C. The Swedish Perioperative Register: Description, validation of data mapping and utility. Acta Anaesthesiol Scand. 2023;67(2):233–9. doi: 10.1111/aas.14174 36424870 Klassifikation av vårdåtgärder (KVÅ) [Internet]. Socialstyrelsen. [cited 2022 Dec 5]. Available from: https://www.socialstyrelsen.se/statistik-och-data/klassifikationer-och-koder/kva/ COVID-19 i svensk intensivvård [Internet]. [cited 2022 Dec 5]. Available from: https://www.icuregswe.org/data--resultat/covid-19-i-svensk-intensivvard/ Statistics Sweden [Internet]. Statistiska Centralbyrån. [cited 2022 Dec 5]. Available from: https://www.scb.se/en/Statistics Jiang W, Carvalho D. COVID-19 effects on operating room cancellations at a pediatric tertiary care hospital: A retrospective cohort study. Ann Med Surg (Lond). 2022;81:104427. doi: 10.1016/j.amsu.2022.104427 36035597 Di Mattia G, Nenna R, Mancino E, Rizzo V, Pierangeli A, Villani A, et al. During the COVID-19 pandemic where has respiratory syncytial virus gone? Pediatr Pulmonol. 2021;56(10):3106–9. doi: 10.1002/ppul.25582 34273135 Minskad antibiotikaanvändning under covid-19-pandemin har inte lett till fler allvarliga infektioner. 2020-12-21. Dnr. 5.7-38411/2020 [cited 2022 Dec 5]. Available from: https://www.socialstyrelsen.se/globalassets/sharepoint-dokument/artikelkatalog/ovrigt/2020-12-7119.pdf Åtgärder mot covid-19 bakom stor minskning av smittsamma sjukdomar — Folkhälsomyndigheten [Internet]. [cited 2022 Dec 5]. Available from: https://www.folkhalsomyndigheten.se/nyheter-och-press/nyhetsarkiv/2021/april/atgarder-mot-covid-19-bakom-stor-minskning-av-smittsamma-sjukdomar/ Kruizinga MD, Peeters D, van Veen M, van Houten M, Wieringa J, Noordzij JG, et al. The impact of lockdown on pediatric ED visits and hospital admissions during the COVID19 pandemic: a multicenter analysis and review of the literature. Eur J Pediatr. 2021;180(7):2271–9. doi: 10.1007/s00431-021-04015-0 33723971 Schranz M, Boender TS, Greiner T, Kocher T, Wagner B, Greiner F, et al. Changes in emergency department utilisation in Germany before and during different phases of the COVID-19 pandemic, using data from a national surveillance system up to June 2021. BMC Public Health. 2023;23(1):799. doi: 10.1186/s12889-023-15375-7 37131165 Hughes HE, Hughes TC, Morbey R, Challen K, Oliver I, Smith GE, et al. Emergency department use during COVID-19 as described by syndromic surveillance. Emerg Med J. 2020;37(10):600–4. doi: 10.1136/emermed-2020-209980 32948621 Hartnett KP, Kite-Powell A, DeVies J, Coletta MA, Boehmer TK, Adjemian J, et al. Impact of the COVID-19 Pandemic on Emergency Department Visits - United States, January 1, 2019-May 30, 2020. MMWR Morb Mortal Wkly Rep. 2020;69(23):699–704. doi: 10.15585/mmwr.mm6923e1 32525856 Ghoshal S, Rigney G, Cheng D, Brumit R, Gee MS, Hodin RA, et al. Institutional Surgical Response and Associated Volume Trends Throughout the COVID-19 Pandemic and Postvaccination Recovery Period. JAMA Netw Open. 2022;5(8):e2227443. doi: 10.1001/jamanetworkopen.2022.27443 35980636 Zhang W, Shen Y, Ou X, Wang H, Liu S. Sleep disordered breathing and neurobehavioral deficits in children and adolescents: a systematic review and meta-analysis. BMC Pediatr. 2024;24(1):70. doi: 10.1186/s12887-023-04511-2 38245707 Bohr C, Shermetaro C. Tonsillectomy and Adenoidectomy. [Updated 2023 Jun 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan. Available from: https://www.ncbi.nlm.nih.gov/books/NBK536942/ Burton MJ, Glasziou PP, Chong LY, Venekamp RP. Tonsillectomy or adenotonsillectomy versus non-surgical treatment for chronic/recurrent acute tonsillitis. Cochrane Database Syst Rev. 2014;2014(11):CD001802. doi: 10.1002/14651858.CD001802.pub3 25407135 Bann DV, Patel VA, Saadi R, Gniady JP, Goyal N, McGinn JD, et al. Impact of coronavirus (COVID-19) on otolaryngologic surgery: Brief commentary. Head Neck. 2020;42(6):1227–34. doi: 10.1002/hed.26162 32270565 El-Boghdadly K, Cook TM, Goodacre T, Kua J, Blake L, Denmark S, et al. SARS-CoV-2 infection, COVID-19 and timing of elective surgery: A multidisciplinary consensus statement on behalf of the Association of Anaesthetists, the Centre for Peri-operative Care, the Federation of Surgical Specialty Associations, the Royal College of Anaesthetists and the Royal College of Surgeons of England. Anaesthesia. 2021;76(7):940–6. doi: 10.1111/anae.15464 33735942 Rosenfeld RM, Tunkel DE, Schwartz SR, Anne S, Bishop CE, Chelius DC, et al. Clinical Practice Guideline: Tympanostomy Tubes in Children (Update). Otolaryngol Head Neck Surg. 2022;166(1_suppl):S1–55. doi: 10.1177/01945998211065662 35138954 Mathers MJ, Sperling H, Rübben H, Roth S. The undescended testis: diagnosis, treatment and long-term consequences. Dtsch Arztebl Int. 2009;106(33):527–32. doi: 10.3238/arztebl.2009.0527 19738919 Gelardi M, Giancaspro R, Fiore V, Fortunato F, Cassano M. COVID-19: Effects of lockdown on adenotonsillar hypertrophy and related diseases in children. Int J Pediatr Otorhinolaryngol. 2020;138:110284. doi: 10.1016/j.ijporl.2020.110284 32861977 Marom T, Pitaro J, Shah UK, Torretta S, Marchisio P, Kumar AT, et al. Otitis Media Practice During the COVID-19 Pandemic. Front Cell Infect Microbiol. 2022;11:749911. doi: 10.3389/fcimb.2021.749911 35071032 Bergh-Eklöf B, Stattin K, Modiri A-R, Frithiof R, Frykholm P. Distribution and outcomes of paediatric anaesthesia services in Sweden: an epidemiological study. Br J Anaesth. 2024;133(4):804–9. doi: 10.1016/j.bja.2024.07.007 39095238 Leo CG, Sabina S, Tumolo MR, Bodini A, Ponzini G, Sabato E, et al. Burnout among healthcare workers in the COVID 19 era: a review of the existing literature. Frontiers in Public Health. 2021;9:750529. Shanafelt TD, Boone S, Tan L, Dyrbye LN, Sotile W, Satele D, et al. Burnout and satisfaction with work-life balance among US physicians relative to the general US population. Arch Intern Med. 2012;172(18):1377–85. Matava C, So J, Williams RJ, Kelley S, ORRACLE-Xtra Group. A Canadian Weekend Elective Pediatric Surgery Program to Reduce the COVID-19-Related Backlog: Operating Room Ramp-Up After COVID-19 Lockdown Ends-Extra Lists (ORRACLE-Xtra) Implementation Study. JMIR Perioper Med. 2022;5(1):e35584. doi: 10.2196/35584 34887242 Abbas A, Samad L, Ozgediz D, Ademuyiwa A, Ameh EA, Banu T, et al. Online action planning forums to develop a roadmap to mitigate the impact of COVID-19 on the delivery of global children’s surgical care. Pediatr Surg Int. 2021;37(9):1221–33. doi: 10.1007/s00383-021-04903-4 33880597 Rosenbäck R, Lantz B, Rosén P. Hospital Staffing during the COVID-19 Pandemic in Sweden. Healthcare (Basel). 2022;10(10):2116. doi: 10.3390/healthcare10102116 36292563 10.1371/journal.pone.0335400.r001 Decision Letter 0 Vilhelmsson Andreas Academic Editor 2025 Andreas Vilhelmsson This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Submission Version 0

5 Jul 2024

Dear Dr. Melander,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by Aug 19 2024 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols . Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols .

We look forward to receiving your revised manuscript.

Kind regards,

Andreas Vilhelmsson, Ph.D

Academic Editor

PLOS ONE

Journal Requirements:

1. When submitting your revision, we need you to address these additional requirements.

Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at 

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and 

https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

2. Thank you for submitting your work to PLOS ONE. At this time, we require the following information in order to proceed with your submission: As you are reporting a retrospective study, please ensure that you have discussed whether all data were fully anonymized before you accessed them. Please include this information in method statement

3. Please update your submission to use the PLOS LaTeX template. The template and more information on our requirements for LaTeX submissions can be found at http://journals.plos.org/plosone/s/latex.

4. We note that you have indicated that there are restrictions to data sharing for this study. For studies involving human research participant data or other sensitive data, we encourage authors to share de-identified or anonymized data. However, when data cannot be publicly shared for ethical reasons, we allow authors to make their data sets available upon request. For information on unacceptable data access restrictions, please see http://journals.plos.org/plosone/s/data-availability#loc-unacceptable-data-access-restrictions. 

Before we proceed with your manuscript, please address the following prompts:

a) If there are ethical or legal restrictions on sharing a de-identified data set, please explain them in detail (e.g., data contain potentially identifying or sensitive patient information, data are owned by a third-party organization, etc.) and who has imposed them (e.g., a Research Ethics Committee or Institutional Review Board, etc.). Please also provide contact information for a data access committee, ethics committee, or other institutional body to which data requests may be sent.

b) If there are no restrictions, please upload the minimal anonymized data set necessary to replicate your study findings to a stable, public repository and provide us with the relevant URLs, DOIs, or accession numbers. Please see http://www.bmj.com/content/340/bmj.c181.long for guidelines on how to de-identify and prepare clinical data for publication. For a list of recommended repositories, please see https://journals.plos.org/plosone/s/recommended-repositories. You also have the option of uploading the data as Supporting Information files, but we would recommend depositing data directly to a data repository if possible.

Please update your Data Availability statement in the submission form accordingly.

5. Please include captions for your Supporting Information files at the end of your manuscript, and update any in-text citations to match accordingly. Please see our Supporting Information guidelines for more information: http://journals.plos.org/plosone/s/supporting-information.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Partly

**********

2. Has the statistical analysis been performed appropriately and rigorously? -->?>

Reviewer #1: No

**********

3. Have the authors made all data underlying the findings in their manuscript fully available??>

The PLOS Data policy

Reviewer #1: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English??>

Reviewer #1: Yes

**********

Reviewer #1: Thank you for providing the opportunity to review this paper, entitled "Swedish pediatric surgery during Covid: A national registry study on the effects of the pandemic on pediatric anesthesia and surgery ". Below, I have provided my evaluation and comments.

I request information about the data source (SPOR) in the method section. How is data recorded into the register? Is it done manually? Are SPOR validated? Most important, to what extent does SPOR cover all operations performed in Sweden? Do centers from both the public and private sectors report to SPOR? Tonsillectomy is often performed in private centers, and sometimes surgery is offered outside the patient's region. Could this impact the validity of the results?

The title contains "…anesthesia and surgery." However, the results do not focus on anesthesia. Are all surgical interventions included in the results performed under anesthesia or specifically general anesthesia? This needs to be clarified.

Only centers that had started reporting to SPOR before 2019 were included. Were all these centers reporting to SPOR throughout the entire period from 2019 to 2022? Or have some centers stopped reporting to the register due to increased workload during the pandemic? This needs to be clarified.

I also request information about the variables retrieved from SPOR and the data arrangement. For example, I find it hard to understand the calculation of the evolution of waiting times. This needs to be clarified in the manuscript.

The large volume of data analyzed means that even small differences can be statistically significant (which could be seen in the analysis of mean age at surgery). Therefore, the results need to be interpreted from the perspective of what is clinically relevant. However, under the statistical section, the significance level that was considered significant is missing.

Several data points appear to be wrong in the tables. For example, the data in Table 1, column 2019, row total-elective, appears to be incorrect (4,067?). The data in Table 3, column Tonsil surgery, row 2019, also seems wrong (1.6?). Please check all data presented in the manuscript.

The discussion is weak and needs to be revised. Some results are briefly discussed, and some statements are poorly substantiated. For instance, the text suggests that ENT surgeries, including tonsillectomy, can be postponed for months or even years without serious harm. The two main indications for tonsil surgery are upper airway obstruction, causing abnormal ventilation during sleep, and infection-related problems such as recurrent tonsillitis. Studies and national guidelines argue that these patients should be prioritized due to short- and long-term consequences of postponed surgery. The discussion section should acknowledge the potential harm of postponed surgeries.

I hope my comments can help!

**********

what does this mean? ). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy

Reviewer #1: No

**********

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/ . PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org . Please note that Supporting Information files do not need this step.

 10.1371/journal.pone.0335400.r002 Author response to Decision Letter 1 Submission Version 1

8 Sep 2024

Dear editors,

We thank the reviewer and editors for their feedback on our manuscript. A rebuttal letter has been uploaded, which aims to respond to the requirements and questions from the journal and the reviewer.

Kindly,

Sixten Melander, corresponding author, on behalf of co-authors

Gunnar Enlund, Helene Engstrand Lilja and Peter Frykholm

Submitted filename: Response to Reviewers.docx

 10.1371/journal.pone.0335400.r003 Decision Letter 1 Vilhelmsson Andreas Academic Editor 2025 Andreas Vilhelmsson This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Submission Version 1

15 Mar 2025

Dear Dr. Melander,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by Apr 29 2025 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols . Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols .

We look forward to receiving your revised manuscript.

Kind regards,

Andreas Vilhelmsson, Ph.D

Academic Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

Reviewer #1: All comments have been addressed

Reviewer #2: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions??>

Reviewer #1: Yes

Reviewer #2: Partly

**********

3. Has the statistical analysis been performed appropriately and rigorously? -->?>

Reviewer #1: Yes

Reviewer #2: N/A

**********

4. Have the authors made all data underlying the findings in their manuscript fully available??>

The PLOS Data policy

Reviewer #1: Yes

Reviewer #2: No

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English??>

Reviewer #1: Yes

Reviewer #2: Yes

**********

Reviewer #1: (No Response)

Reviewer #2: This manuscript addresses an important and timely topic, contributing to our understanding of long-term healthcare implications post-COVID-19 on healthcare systems. It is a commendable effort to analyze data from a national cohort.

However, significant revisions are necessary to enhance the methodological rigor and ensure the claims are well-supported by the presented data. Specifically, the conclusions regarding long-term effects of COVID-19 require a more cautious interpretation, given the descriptive nature of the retrospective cohort study and potential biases in the analysis. Furthermore, a more robust time series analysis and careful control for confounding factors are critical to substantiate the findings.I do not agree with the concluding claim that the provided data is evidence for long-term effects of COVID-19, at least based on the evidence provided so far. We observe data indicating an increasing overall stress burden on healthcare worldwide due to various reason that also include i.e. changing demographics, rising costs etc.. These factors are and probably cannot addressed in a cohort study based on retrospective secondary data.

Introduction

1) Include more references; ensure all claims are supported by citations.

Methods

1) Report the methods and study characteristics more thoroughly.

2) Explain the rationale for selecting 2019 as the baseline year. Please adjust the research question and objectives accordingly. Elaborate on why comparisons were not made to an average of the years before.

3) Provide details of the study setting, including the exact number of study centers and the variables used for secondary analyses (e.g., level of care).

4) Include comprehensive details of the cohort, including eligibility criteria and the sources and methods of participant selection.

5) Clearly define all outcomes, exposures, predictors, potential confounders, and effect modifiers.

6) Expand on data sources and measurement methods, including a discussion of the registry as a secondary data source and its likely purpose for billing.

7) Describe efforts to address potential sources of bias in the registry or clarify if this is a convenience sample.

8) Explain how quantitative variables were handled in the analyses. If applicable, describe groupings and provide a rationale for the chosen groupings (e.g., why focus on the 20 most common procedures in 2019 rather than overall procedures?).

9) Provide the rationale for investigating the mean age at the time of surgery and how it relates to the study objectives.

10) Include more robust time-series analyses, such as interrupted time-series analysis (Especially given the claim in the conclusion).

10.1) Consider the influence of different COVID-19 waves, comparing them to baseline and different timings ((i.e. https://doi.org/10.1177/014107682096244, https://doi.org/10.1186/s12889-023-15375-7, https://doi.org/10.1371/journal.pgph.0000029).

10.2) Consider causal impact analysis (https://doi.org/10.2147/rmhp.s459307).

13) Explain how missing data were handled in the study.

14) Provide the r source code for the analysis.

Results

15) Clarify whether cases were excluded and provide details about the overall initial sample. Report the number of individuals at each stage of the study (e.g., eligible, examined for eligibility, confirmed eligible, included).

16) If possible, include a cohort flow chart detailing exclusions and other relevant stages.

17) Ensure all tables in the PDF are fully included to allow for a complete evaluation of the results.

18) Align the results with the research question (hypothesis) and objectives. For instance, results such as age characteristics do not fit the stated focus. Adjust the methods and introduction if the scope is broader than the stated patterns of reduction.

18.1) In particular state the rationale behind studying the age. It is not stated in the introduction, methods or discussion what it hast to do with patterns in the reduction of pediatric procedures or if it is a cofactor effecting reduction. The effect of age is not statistically addressed.

19) no infferential results are presented, aside from the statement in the methods section.

Discussion

19) Provide a cautious overall interpretation of the results and discuss their generalizability.

20) Address the effect of comparing one pre-COVID year to multiple post-COVID years.

21) Discussion evaluation is challenging due to missing results (e.g., incomplete tables).

22) Clarify the claim that "the strength of the present study is that it provides detailed data from a national perioperative database including almost all major Swedish hospitals with pediatric anesthesia." Provide evidence to support this claim and elaborate on what "almost all major" entails, as well as its implications for representativeness.

23) Discuss the study's limitations in more detail, particularly regarding the chosen methods. Consider potential sources of bias or imprecision, addressing both their direction and magnitude.

24) Please relate to other studys that study the impact of covid on admission and surgeries.

Overall

24) Reduce the number of figures in the appendix to only those that are directly relevant, I was overwhelmed

25) I cannot fully evaluate the manuscript, as not all data are included (tables do not fit the manuscript).

**********

what does this mean? ). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy

Reviewer #1: No

Reviewer #2: Yes:  Jonas Bienzeisler

**********

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/ . PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org . Please note that Supporting Information files do not need this step.

 10.1371/journal.pone.0335400.r004 Author response to Decision Letter 2 Submission Version 2

22 Apr 2025

Response to Reviewers

Dear editors and reviewers,

We thank the reviewers for their feedback on our manuscript. This is a rebuttal letter

that aims to respond to the questions from the reviewers. We respond to the

questions raised one-by-one below.

Kindly,

Sixten Melander, corresponding author, on behalf of co-authors

Gunnar Enlund, Helene Engstrand Lilja and Peter Frykholm

Reviewer #2: This manuscript addresses an important and timely topic, contributing

to our understanding of long-term healthcare implications post-COVID-19 on

healthcare systems. It is a commendable effort to analyze data from a national

cohort.

However, significant revisions are necessary to enhance the methodological rigor and

ensure the claims are well-supported by the presented data. Specifically, the

conclusions regarding long-term effects of COVID-19 require a more cautious

interpretation, given the descriptive nature of the retrospective cohort study and

potential biases in the analysis. Furthermore, a more robust time series analysis and

careful control for confounding factors are critical to substantiate the findings. I do not

agree with the concluding claim that the provided data is evidence for long-term

effects of COVID-19, at least based on the evidence provided so far. We observe

data indicating an increasing overall stress burden on healthcare worldwide due to

various reason that also include i.e. changing demographics, rising costs etc.. These

factors are and probably cannot addressed in a cohort study based on retrospective

secondary data.

Thank you for this comprehensive review with constructive comments and helpful

suggestions. We have revised the conclusion and have added a discussion in the

limitations on the problems of cause and effect and confounding. Obviously, we

cannot provide the complete picture in this retrospective study. We have also added

a rudimentary time series analysis by the addition of data from the official four waves

of the pandemic.

Introduction

1) Include more references; ensure all claims are supported by citations.

We have provided new references, marked in red.

Methods

1) Report the methods and study characteristics more thoroughly.

We have expanded the methods section as suggested.

2) Explain the rationale for selecting 2019 as the baseline year. Please adjust the

research question and objectives accordingly. Elaborate on why comparisons were

not made to an average of the years before.

The reason for using only 2019 as the baseline year was that this was the first year in

which almost all Swedish Hospitals had joined the Registry. Ideally, we would have

had access to complete baseline data from at least three years but since the Register

was still lacking data from several major centers, inclusion of data reported earlier

than 2019 would have been less reliable.

3) Provide details of the study setting, including the exact number of study centers

and the variables used for secondary analyses (e.g., level of care).

We have provided the number of hospitals in each category contributing with data to

SPOR.

4) Include comprehensive details of the cohort, including eligibility criteria and the

sources and methods of participant selection.

SPOR is national registry with the aim of including all Swedish hospitals with

anesthesia and surgery services. All hospitals connected to SPOR were therefore

eligible for inclusion in the present study. We received a complete dataset from

SPOR for the studied period and excluded only those 9 hospitals that had not

reported data from the complete study period. This was mentioned in the limitations.

We decided from the start to exclude children <16 years old, and they were not in our

initial data. A cohort flow chart has been added for clarification.

5) Clearly define all outcomes, exposures, predictors, potential confounders, and

effect modifiers.

We have tried to more clearly define outcomes and confounders in the methods

section.

6) Expand on data sources and measurement methods, including a discussion of the

registry as a secondary data source and its likely purpose for billing.

We have added some text to further describe SPOR.

7) Describe efforts to address potential sources of bias in the registry or clarify if this

is a convenience sample.

We have added the information of convenience sample in statistical methods.

8) Explain how quantitative variables were handled in the analyses. If applicable,

describe groupings and provide a rationale for the chosen groupings (e.g., why focus

on the 20 most common procedures in 2019 rather than overall procedures?).

Quantitative variables have been clearly described and the rationale for groupings

has been expanded in the methods. We did focus on reduction in overall procedures

as the primary outcome. The choice of more detailed analysis of the 20 most

common procedures was arbitrary, but was included to attempt to provide more detail

for common procedures. It would not have been feasible to report data at this level

for each and every type of procedure, as the total number of different procedure

codes was 3,276, most of them with low total numbers of registered entries.

9) Provide the rationale for investigating the mean age at the time of surgery and how

it relates to the study objectives.

The purpose of the study was to investigate patterns and possible effects of the

reduced capacity during the pandemic. Mean age at surgery for a specific procedure

could be a marker for postponing specific elective operations. Since data on when a

procedure is planned and performed were included in the extracted dataset, we also

decided to look at waiting times.

10) Include more robust time-series analyses, such as interrupted time-series

analysis (Especially given the claim in the conclusion).

Regarding time series analysis, Figure 1 describes a time series analysis with weekly

changes in case-load against the backdrop of ICU admissions as a measure of the

intensity of the pandemic. We have added data on changes during the pandemic

waves as a rudimentary intervention time series analysis.

10.1) Consider the influence of different COVID-19 waves, comparing them to

baseline and different timings ((i.e. https://doi.org/10.1177/014107682096244,

https://doi.org/10.1186/s12889-023-15375-7,

https://doi.org/10.1371/journal.pgph.0000029).

Thank you for this suggestion. We have added information on changes during the

waves in Fig 2 and Table 2.

10.2) Consider causal impact analysis (https://doi.org/10.2147/rmhp.s459307).

It was not in the scope of the present study include a causal impact analysis since it

would have required additional data.

13) Explain how missing data were handled in the study.

The SPOR has an excellent automated data collection system with extensive

validation that provides complete datasets for the variables we analysed. SPOR

provides several other interesting variables such as adverse events (including grade)

that are less well validated and therefore prone to varying amounts of missing data.

This is why we focused on core data such as date, age, and type of procedure.

14) Provide the r source code for the analysis.

This is the source code:

library(openxlsx)

infile1 <- "K:/Academy/UU/Frykholm/Indata/Tabell 1 HT23_utan_losen.xlsx"

adb <- read.xlsx(infile1)

orig <- adb

colnames(adb)[3:6] <- paste0("X", colnames(adb)[3:6])

colnames(adb)[c(9,11,13)] <- c("p1", "p2", "p3")

adb$X2020 <- as.numeric(gsub(" |\\(.*", "", adb$X2020))

adb$X2021 <- as.numeric(gsub(" |\\(.*", "", adb$X2021))

adb$X2022 <- as.numeric(gsub(" |\\(.*", "", adb$X2022))

adb$X2022 <- as.numeric(gsub(" |\\(.*", "", adb$X2022))

colnames(adb)[12] <- "19_22"

adb[,c("20_21", "p4", "20_22", "p5", "21_22", "p6")] <- NA

for(i in 1:17){

adb[i,"19_20"] <- poisson.test(c(adb$X2019[i],

adb$X2020[i]),c(adb$X2019[18],adb$X2020[18]))$estimate

adb[i,"p1"] <- poisson.test(c(adb$X2019[i],

adb$X2020[i]),c(adb$X2019[18],adb$X2020[18]))$p.value

adb[i,"19_21"] <- poisson.test(c(adb$X2019[i],

adb$X2021[i]),c(adb$X2019[18],adb$X2021[18]))$estimate

adb[i,"p2"] <- poisson.test(c(adb$X2019[i],

adb$X2021[i]),c(adb$X2019[18],adb$X2021[18]))$p.value

adb[i,"19_22"] <- poisson.test(c(adb$X2019[i],

adb$X2022[i]),c(adb$X2019[18],adb$X2022[18]))$estimate

adb[i,"p3"] <- poisson.test(c(adb$X2019[i],

adb$X2022[i]),c(adb$X2019[18],adb$X2022[18]))$p.value

adb[i,"20_21"] <- poisson.test(c(adb$X2020[i],

adb$X2021[i]),c(adb$X2020[18],adb$X2021[18]))$estimate

adb[i,"p4"] <- poisson.test(c(adb$X2020[i],

adb$X2021[i]),c(adb$X2020[18],adb$X2021[18]))$p.value

adb[i,"20_22"] <- poisson.test(c(adb$X2020[i],

adb$X2022[i]),c(adb$X2020[18],adb$X2022[18]))$estimate

adb[i,"p5"] <- poisson.test(c(+adb$X2020[i],

adb$X2022[i]),c(adb$X2020[18],adb$X2022[18]))$p.value

adb[i,"21_22"] <- poisson.test(c(adb$X2021[i],

adb$X2022[i]),c(adb$X2021[18],adb$X2022[18]))$estimate

adb[i,"p6"] <- poisson.test(c(adb$X2021[i],

adb$X2022[i]),c(adb$X2021[18],adb$X2022[18]))$p.value

}

write.xlsx(adb, "K:/Academy/UU/Frykholm/Poisson_2023-11-09.xlsx")

Results

15) Clarify whether cases were excluded and provide details about the overall initial

sample. Report the number of individuals at each stage of the study (e.g., eligible,

examined for eligibility, confirmed eligible, included).

This information has been added.

16) If possible, include a cohort flow chart detailing exclusions and other relevant

stages.

Thank you for this suggestion. A flow-chart has been added.

17) Ensure all tables in the PDF are fully included to allow for a complete evaluation

of the results.

The tables have been reformatted

18) Align the results with the research question (hypothesis) and objectives. For

instance, results such as age characteristics do not fit the stated focus. Adjust the

methods and introduction if the scope is broader than the stated patterns of

reduction.

We have expanded our methods section, please see answer below for clarification.

18.1) In particular state the rationale behind studying the age. It is not stated in the

introduction, methods or discussion what it hast to do with patterns in the reduction of

pediatric procedures or if it is a cofactor effecting reduction. The effect of age is not

statistically addressed.

We hypothesized that massive postponement of minor surgery could lead to children

having their surgery at an older age. This issue is explored in table 3. We think

confidence intervals is an appropriate way to report this kind of data rather than a

long list of p-values.

19) no infferential results are presented, aside from the statement in the methods

section.

This is not a classic epidemiological study. We had access to data on procedures and

the age and sex of the patients but no data on confounders such as socioeconomic

factors. We did however use poisson regression to compare the pandemic years with

the preceding year regarding the number of performed procedures in relation to the

population during the respective years.

Discussion

19) Provide a cautious overall interpretation of the results and discuss their

generalizability.

We have revised the interpretation and conclusion.

20) Address the effect of comparing one pre-COVID year to multiple post-COVID

years.

Added this discussion to the limitations.

21) Discussion evaluation is challenging due to missing results (e.g., incomplete

tables).

We apologize for this inconvenience. Apparently the tables were truncated at page

margins. This has been addressed in the current version.

22) Clarify the claim that "the strength of the present study is that it provides detailed

data from a national perioperative database including almost all major Swedish

hospitals with pediatric anesthesia." Provide evidence to support this claim and

elaborate on what "almost all major" entails, as well as its implications for

representativeness.

Sweden has a tax-funded healthcare system and the vast majority of pediatric

surgery is performed in government-run hospitals which are 100% covered in SPOR.

A few small private clinics perform office-based procedures in children without

reporting their data to SPOR. We estimate that less than 2000 procedures with GA

are performed annually in Swedish private clinics, which would amount to less than

1% missing data for this reason. We have added info to the limitations section.

23) Discuss the study's limitations in more detail, particularly regarding the chosen

methods. Consider potential sources of bias or imprecision, addressing both their

direction and magnitude.

The limitations section was expanded.

24) Please relate to other studys that study the impact of covid on admission and

surgeries.

We have expanded our discussion on the topic of admissions and volume of surgery

and added four more references.

Overall

24) Reduce the number of figures in the appendix to only those that are directly

relevant, I was overwhelmed

To overwhelm was not our intention. We included these figures to provide detailed

regional data but detailed comparative analysis was not within the scope of the

present paper.

25) I cannot fully evaluate the manuscript, as not all data are included (tables do not

fit the manuscript).

Tables have been reformatted.

Submitted filename: Response_to_Reviewers_auresp_2.docx

 10.1371/journal.pone.0335400.r005 Decision Letter 2 Vilhelmsson Andreas Academic Editor 2025 Andreas Vilhelmsson This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Submission Version 2

31 Jul 2025

Dear Dr. Melander,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by Sep 14 2025 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols . Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols .

We look forward to receiving your revised manuscript.

Kind regards,

Andreas Vilhelmsson, Ph.D

Academic Editor

PLOS ONE

Journal Requirements:

1. If the reviewer comments include a recommendation to cite specific previously published works, please review and evaluate these publications to determine whether they are relevant and should be cited. There is no requirement to cite these works unless the editor has indicated otherwise. 

2. Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

Reviewer #3: All comments have been addressed

Reviewer #4: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions??>

Reviewer #3: Yes

Reviewer #4: Partly

**********

3. Has the statistical analysis been performed appropriately and rigorously? -->?>

Reviewer #3: Yes

Reviewer #4: No

**********

4. Have the authors made all data underlying the findings in their manuscript fully available??>

The PLOS Data policy

Reviewer #3: Yes

Reviewer #4: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English??>

Reviewer #3: Yes

Reviewer #4: No

**********

Reviewer #3: The paper has addressed the issues previously raised and is now of sufficient quality for publication.

Reviewer #4: This manuscript investigates the changes in surgical volume in Sweden before and after the COVID-19 pandemic. The topic is of considerable interest, and the reported decrease in elective procedures aligns with many previous studies.

However, the submitted manuscript is very difficult to read and review. The authors use numerous unconventional abbreviations, particularly in the tables, and there is no clear distinction between the table legends and the main text, which severely hinders readability and interpretation.

In addition, the right margin of the manuscript is filled with unnecessary grey space created by Microsoft Word's comment function, which compresses the body text and makes it even more difficult to read. The manuscript also contains many typographical errors and nonstandard terminology, and it clearly should have undergone professional editing by a native English speaker before submission.

I strongly recommend that the authors revise the manuscript with greater consideration for reviewers, who are volunteering their time and effort. The manuscript should be written in a way that facilitates the review process.

Below are some specific questions and concerns regarding the manuscript:

Please specify the exact dates that define the "four different waves" of the pandemic. How were these definitions established?

In Table 1, please provide an explanation for the labels "19_20," "19_21," and "19_22." The legend states: "rate-ratio comparisons of the number of procedures during the different years, using a Poisson regression, adjusted for the Swedish population at risk during that specific year, using data from Statistics Sweden." However, it seems that these are simply the inverse of the proportion values. For example, the first entry (1.17 for 19_20) appears to be calculated by dividing 57099 by 49000, which corresponds to the inverse of 86% shown next to 49000. What is the actual basis for the reported p-values?

Does "EMB30" stand for "Distribution of waiting times for adenoidectomy"? Please clarify.

In the phrase "Forearm or elbow X. Closed reduction," what does "X" mean? This expression appears multiple times but is not standard terminology.

Does “extraction implant” mean “implant removal”? Please use established surgical terminology.

Does “Lap. excision” refer to laparoscopic excision? Please spell it out.

“Retentio testis” is a diagnosis, not a surgical procedure.

What is meant by "Diagnostic exam"? Please specify what kind of diagnostic procedure is being referred to.

Table 3 contains misaligned indentations and spacing, making it difficult to read. Please reconstruct the table for clarity.

"ENT" in "ENT/oral surgery" is not an internationally standardized abbreviation. Please provide the full term and its definition in both the abstract and the main text.

The Discussion section contains too many paragraphs. Some paragraphs consist of only one sentence, and others are divided without logical flow. This makes the text difficult to follow and does not adhere to standard academic writing conventions. Please restructure the Discussion for better coherence and readability.

The authors state that "The strength of the present study is that it provides detailed data from a national perioperative database including almost all major Swedish hospitals with pediatric anesthesia." However, this claim is not substantiated by the content of the manuscript. The level of detail in the data is not sufficient to be considered a particular strength.

In the Discussion, the phrase "nursing staff shortages in the wake of the pandemic" is used. Does this imply that there was a substantial reduction in the number of nurses in Sweden due to the pandemic? Please elaborate and provide references if possible.

**********

what does this mean? ). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy

Reviewer #3: No

Reviewer #4: No

**********

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/ . PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org

 10.1371/journal.pone.0335400.r006 Author response to Decision Letter 3 Submission Version 3

13 Sep 2025

Response to Reviewers

Dear editor and reviewers,

We thank the reviewers for their feedback on our manuscript. Please find below in italics our replies the questions and comments from the reviewers.

Kindly,

Sixten Melander, corresponding author, on behalf of co-authors

Gunnar Enlund, Helene Engstrand Lilja and Peter Frykholm

1. This manuscript investigates the changes in surgical volume in Sweden before and after the COVID-19 pandemic. The topic is of considerable interest, and the reported decrease in elective procedures aligns with many previous studies.

However, the submitted manuscript is very difficult to read and review. The authors use numerous unconventional abbreviations, particularly in the tables, and there is no clear distinction between the table legends and the main text, which severely hinders readability and interpretation.

In addition, the right margin of the manuscript is filled with unnecessary grey space created by Microsoft Word's comment function, which compresses the body text and makes it even more difficult to read. The manuscript also contains many typographical errors and nonstandard terminology, and it clearly should have undergone professional editing by a native English speaker before submission.

We apologise for the unfortunate formatting errors and unusual abbreviations. We have revised accordingly.

Specifically, we have limited abbreviations, decreased font size in table legend (which follows PLOS1 formatting guidelines) and updated table titles.

2. Please specify the exact dates that define the "four different waves" of the pandemic. How were these definitions established?

As stated in the 2nd paragraph of the introduction, the definition of the waves was taken from a report from the Swedish NBHW: “According to another report from the NBHW [4], there have been four major waves of Covid-19 in Sweden. The first wave was defined to encompass March - September 2020, the second wave October 2020 - January 2021, the third wave February - June 2021 and the fourth wave July 2021 - April 2022 respectively.”

Upon further review of this reference, a slight error has been noted. The fourth wave was defined as July 2021 – March 2022, meaning we incorrectly included April in our analysis of the fourth wave. Our text as well as the numbers in table 2 have been corrected. The differences are marginal and does not change our conclusions. We have also corrected the timeline on the x-axis in Fig 2.

The citation in the text is as follows, although it is written in Swedish:

4. Uppdrag att stödja regionernas hantering av uppdämda vårdbehov samt följa och analysera väntetider i hälso- och sjukvården. Regeringsbeslut 2020-06-25. Dnr S2020/05634/FS [cited 2025 Dec 5] Available from: https://www.regeringen.se/contentassets/67003d0bc0c54da68d5446c5de6dfb59/uppdrag-att-stodja-regionernas-hantering-av-uppdamda-vardbehov-web.pdf

For clarification we added another citation regarding the definitions of the waves, from the Swedish NBHW:

5. Regeringsuppdrag att stödja regionernas hantering av uppdämda vårdbehov samt följa och analysera väntetider i hälso- och sjukvården – Slutrapport mars 2022. [Internet]. Socialstyrelsen. [cited 2025 Sept 1]. Available from: https://www.socialstyrelsen.se/contentassets/af10f61ee18245dbb1543cd1773002e3/ 2022-3-7798.pd

3. In Table 1, please provide an explanation for the labels "19_20," "19_21," and "19_22." The legend states: "rate-ratio comparisons of the number of procedures during the different years, using a Poisson regression, adjusted for the Swedish population at risk during that specific year, using data from Statistics Sweden." However, it seems that these are simply the inverse of the proportion values. For example, the first entry (1.17 for 19_20) appears to be calculated by dividing 57099 by 49000, which corresponds to the inverse of 86% shown next to 49000. What is the actual basis for the reported p-values?

We have updated table 1 and its legend, removing the inverse calculations and putting the p-values in the same cells as the number of procedures and the percentage ratios for clarification purposes. The labels "19_20," "19_21," and "19_22." have been removed. The p-values were calculated as stated above and in the statistical methods.

4. Does "EMB30" stand for "Distribution of waiting times for adenoidectomy"? Please clarify.

In the phrase "Forearm or elbow X. Closed reduction," what does "X" mean? This expression appears multiple times but is not standard terminology.

Does “extraction implant” mean “implant removal”? Please use established surgical terminology.

Does “Lap. excision” refer to laparoscopic excision? Please spell it out.

“Retentio testis” is a diagnosis, not a surgical procedure.

What is meant by "Diagnostic exam"? Please specify what kind of diagnostic procedure is being referred to.

Table 3 contains misaligned indentations and spacing, making it difficult to read. Please reconstruct the table for clarity.

"ENT" in "ENT/oral surgery" is not an internationally standardized abbreviation. Please provide the full term and its definition in both the abstract and the main text.

We have clarified these questions in our manuscript and corrected formatting errors within table 3. In short, EMB30 is the swedish surgical code for adenoidectomy and has been removed, “X” is short for “fracture”, “extraction” has been changed to “removal”, “Lap.” Is short for “laparoscopic”, retentio testis has been changed to “Operation for undescended or ectopic testis.”, “Diagnostic exam” is explained in the table legend as “Diagnostic procedures under general anesthesia or sedation performed by anesthesiologists” and “ENT” is now clarified as “Ear, Nose and Throat”.

5. The Discussion section contains too many paragraphs. Some paragraphs consist of only one sentence, and others are divided without logical flow. This makes the text difficult to follow and does not adhere to standard academic writing conventions. Please restructure the Discussion for better coherence and readability.

The Discussion has been updated to improve coherence and flow.

8. The authors state that "The strength of the present study is that it provides detailed data from a national perioperative database including almost all major Swedish hospitals with pediatric anesthesia." However, this claim is not substantiated by the content of the manuscript. The level of detail in the data is not sufficient to be considered a particular strength.

Thank you for noting this, we agree and have removed the word “detailed”.

9. In the Discussion, the phrase "nursing staff shortages in the wake of the pandemic" is used. Does this imply that there was a substantial reduction in the number of nurses in Sweden due to the pandemic? Please elaborate and provide references if possible.

We have elaborated briefly on this topic, adding a reference:

35. Rosenbäck R, Lantz B, Rosén P. Hospital Staffing during the COVID-19 Pandemic in Sweden. Healthcare (Basel). 2022 Oct 21;10(10):2116. doi: 10.3390/healthcare10102116. PMID: 36292563; PMCID: PMC9602433.

 10.1371/journal.pone.0335400.r007 Decision Letter 3 Vilhelmsson Andreas Academic Editor 2025 Andreas Vilhelmsson This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Submission Version 3

12 Oct 2025

The Covid-19 pandemic in Sweden: prolonged and unevenly distributed effects on the volume of pediatric anesthesia and surgery demonstrated by data from the Swedish Perioperative Register

PONE-D-24-03764R3

Dear Dr. Melander,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice will be generated when your article is formally accepted. Please note, if your institution has a publishing partnership with PLOS and your article meets the relevant criteria, all or part of your publication costs will be covered. Please make sure your user information is up-to-date by logging into Editorial Manager at Editorial Manager®  and clicking the ‘Update My Information' link at the top of the page. For questions related to billing, please contact billing support .

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Andreas Vilhelmsson, Ph.D

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

 10.1371/journal.pone.0335400.r008 Acceptance letter Vilhelmsson Andreas Academic Editor 2025 Andreas Vilhelmsson This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

PONE-D-24-03764R3

PLOS ONE

Dear Dr. Melander,

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now being handed over to our production team.

At this stage, our production department will prepare your paper for publication. This includes ensuring the following:

* All references, tables, and figures are properly cited

* All relevant supporting information is included in the manuscript submission,

* There are no issues that prevent the paper from being properly typeset

You will receive further instructions from the production team, including instructions on how to review your proof when it is ready. Please keep in mind that we are working through a large volume of accepted articles, so please give us a few days to review your paper and let you know the next and final steps.

Lastly, if your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

You will receive an invoice from PLOS for your publication fee after your manuscript has reached the completed accept phase. If you receive an email requesting payment before acceptance or for any other service, this may be a phishing scheme. Learn how to identify phishing emails and protect your accounts at https://explore.plos.org/phishing.

If we can help with anything else, please email us at customercare@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr Andreas Vilhelmsson

Academic Editor

PLOS ONE