Antibiotic resistance pattern of Salmonella enterica typhi infection in the paediatric population at a tertiary level hospital

Background: Enteric fever is an important public health condition in developing countries. Antibiotic resistance patterns in Salmonella enterica typhi ( S. typhi ) infections are constantly changing. Continual surveillance of resistance levels of S. typhi is critical for clinicians to update antibiotic options. Objectives : To evaluate the current trends in antibiotic sensitivity and resistance to S. typhi in children in developing countries. Method: A cross sectional observational study was carried out on 102 children aged 6 months to 5 years with culture positive S. typhi infection in a tertiary care hospital in North India. Antibiotic susceptibility information of S. typhi was collected and the pattern of antibiotic resistance was analysed. Results: S. typhi showed a sensitivity of 78.4% to ampicillin and 99% to trimethoprim+ sulfamethoxazole which were the previously used antibiotics. However, it showed 100% resistance to ciprofloxacin and nalidixic acid. Of the currently used first line IV antibiotics, there was a 88.4% sensitivity to ceftriaxone and a 98% sensitivity to meropenem. Conclusions: The study concluded that there is re-emergence of antibiotic sensitivity of S. typhi to earlier first line drugs like ampicillin and trimethoprim– sulfamethoxazole. (Key words: Enteric

Ceftriaxone and cefixime are currently the first line of antibiotic treatment for typhoid fever 4 .Along with the 3 rd generation cephalosporins, azithromycin is used as firstline therapy and ampicillin and co-trimoxazole as stepdown therapy in paediatric enteric fever 5 .With inappropriate use of antibiotics, there is an increasing trend of large number of multidrug-resistant (MDR) and extended drug-resistant (XDR) typhoid cases and it is becoming a public health emergency 6 .
Antibiotic resistance patterns in S. typhi infections are constantly changing 7 .Continual surveillance of resistance levels is critical for clinicians to update antibiotic options, but it is often lacking in resource-poor regions of the world with the highest disease burden.Re-emergence of susceptibility to first line drugs has been noted in enteric fever 8 .

Objectives
To evaluate the current trends in antibiotic sensitivity and resistance to S. typhi in children in developing countries

Method
It was a cross sectional observational study carried out in the Department of Paediatrics of a tertiary care hospital of North India from July 2019 to January 2021.Blood culture and antibiotic sensitivity was done in all clinical enteric fever cases aged 6 months to 12 years.All patients whose blood cultures grew S. typhi (both fresh and relapsed cases) were enrolled in the study.Patients excluded were those who were culture negative and those with Salmonella paratyphi infections.Antibiotic susceptibility information was collected and the pattern of antibiotic resistance was analysed in the culture positive cases.
Ethical issues: Approval for the study was obtained from the Institutional Ethics Committee of the Base Hospital and Army College of Medical Sciences, Delhi Cantt, India (IEC BHDC/ 50 of 2019) on 26.07.2019.Written informed consent was obtained from the parents/caregivers of the participants.

Statistical analysis:
Patient details and investigations were collected on case record sheets and entered in Microsoft Excel Version 2017 (Microsoft Corporation, New York, USA).Results were analysed and statistically evaluated using Microsoft Excel and Statistical Package for Social Sciences (SPSS statistics for Windows, Version 23, Armonk, NY: IBM Corp).Continuous variables were presented as mean ± SD.Categorical variables were expressed as frequencies and percentages.Pearson's Chisquare test was used to determine if there is a relationship between two variables (antibiotic susceptibility pattern of previously and currently used drugs).p<0.05 was considered statistically significant.

Results
The study was conducted on 102 children with enteric fever (both fresh and relapsed cases) whose blood culture grew S. typhi.Antibiotic susceptibility information of S. typhi was collected and pattern of the antibiotic resistance was analysed.The demographic and clinical characteristics of these patients are shown in Table 1 and the laboratory parameters are shown in Table 2. Figure 1 shows the antibiotics used for the treatment of enteric fever patients.Figure 2 and Figure 3 show the sensitivity and resistance pattern of the Salmonella typhi organisms grown in the present study to previously used antibiotics and the currently used antibiotics respectively.
Cross tabulation of previously used and currently used antibiotics for enteric fever was done which showed that ampicillin and trimethoprim-sulfamethoxazole were as sensitive as ceftriaxone and meropenem against S. typhi (p value <0.001) and the correlation was statistically significant (Table 3).
The present study reported no MDR/XDR strains (MDR: resistant to ampicillin, chloramphenicol, trimethoprimsulfamethoxazole; XDR: resistance to MDR drugs, fluoroquinolones and third generation cephalosporins) 12,13 .The study also revealed salmonella typhi strains were sensitive to ampicillin (78.4%), and trimethoprim-sulfamethoxazole (99%).However, they were 100% resistant to nalidixic acid and ciprofloxacin.Balaji C, et al reported that salmonella typhi isolates showed 100% resistance to ampicillin in contrast to this study 14 .Patel SR, et al reported the sensitivity rate of trimethoprim-sulfamethoxazole to be 80.9% in their study 15 .Jain S, et al. reported 19% sensitivity rate of Salmonella typhi for nalidixic acid and 96% for ciprofloxacin in contrast to the present study 16 .Sharma P, et al reported ciprofloxacin susceptibility was 71.3% for S. typhi in their study 17 .This study reported 88.4% sensitivity to ceftriaxone and 98% to meropenem.Susceptibility pattern for cefixime and azithromycin could not be tested in the hospital laboratory.In contrast, Satti ML, et al reported 85.5% of cases were ceftriaxoneresistant and only 14.4% were ceftriaxone-sensitive 18 .Dahiya S, et al reported 100% were susceptible to ceftriaxone 4 .Ali Shah SA, et al reported 48% S, typhi cases were resistant to meropenem 7 .
Ceftriaxone was the main drug used in the present study which resulted in fever defervescence within a week in 90% cases.A statistically significant correlation was found between ampicillin and ceftriaxone proving it to be as sensitive as ceftriaxone.The results suggest that ampicillin can also yield similar clinical results as ceftriaxone.However, when compared to meropenem the result was not significant making meropenem superior to ampicillin.
Similarly, the sensitivity rate of trimethoprimsulfamethoxazole is better compared to ceftriaxone.The correlation between trimethoprim-sulfamethoxazole and meropenem was found to be significant indicating trimethoprim-sulfamethoxazole is as sensitive as meropenem.
S. typhi keeps changing its antimicrobial susceptibility pattern.Primary drugs are showing less resistance due to their infrequent usage whereas 3 rd generation cephalosporins started showing resistance towards typhoid bacilli.With improper use of antibiotics, rising trends of multidrug-resistant (MDR) and extended drugresistant (XDR) typhoid are reported.For better clinical management it is important to know the recent susceptibility trend of the area.Susceptibility pattern must be closely monitored in view of emerging resistance to currently used drugs.
This study was undertaken to determine the antibiotic use and susceptibility pattern in enteric fever in children presenting to a tertiary care centre in North India.With many reports of ceftriaxone resistance and absence of any new drug, studies are being conducted to understand the combination of antibiotics in the treatment of enteric fever.In a conclave on enteric fever by the Association of Physicians of India (API), it was recommended that combination therapy should be used in case of fever lasting for seven days and if no clinical improvement was observed with monotherapy 19,20 .
The fixed-dose combinations are in use but without any studies to support their advantage.Before the fixed-dose combinations are prescribed, a second antibiotic should be added only on clinical judgment in selected cases.Also, there is a need to improve preventive measures like safe water supply and by developing new vaccines that are effective against S. typhi as there is no new drug currently available.
The limitation of the present study was that the susceptibility pattern of drugs like chloramphenicol, azithromycin and cefixime was not tested in the hospital laboratory.While multidrug therapy in enteric fever must be given in selected cases only, role of many fixed drug combinations available needs to be studied.The study highlights the need for renewed guidelines in the treatment of typhoid fever using multidrug therapy combining previously and currently used drugs in the time of increasing antimicrobial resistance in S. typhi 4 .

Conclusions
The study concludes that there is re-emergence of antibiotic sensitivity of S. typhi to earlier first line drugs like ampicillin and trimethoprim-sulfamethoxazole.However, commonly used drugs -fluoroquinolones like nalidixic acid and ciprofloxacin have shown resistance to S. typhi.