Cardiovascular diseases (CVDs), mainly consisting of coronary heart disease (CHD) and stroke, are the number one killer in China [1]. While most western countries have witnessed a gradual decline of the CVD epidemic in the past decades [2–4], China has facing an unprecedented increase since 1990 due to its rapid economic development and associated changes in lifestyles [1, 5, 6]. By 2008, the prevalence rates of CHD and stroke in China had reached 77 and 97 per 10,000, respectively [7]. It is estimated that China will have an additional 21 million CVD cases by 2030 [8]. There is an urgent need to establish a population based real-time surveillance system that enables a systematic and continuous collection of data on CVD cases to monitor the progress of the epidemic [9]. A well-functioning surveillance system also provides evidence-based information to health policy-makers [10]. However, developing countries normally lack the resources and capacity to implement such a sophisticated system for CVD surveillance [11]. The Monitoring Trends and Determinants in Cardiovascular Disease (MONICA) project was established by the World Health Organization (WHO) in 1980s. But it only covered a small proportion of the population in developing countries. China set up the National Stroke Registry in 2007 [12] and subsequently the Acute Myocardial Infarction Registry in 2013 [13]. However, both systems were hospital-based, only tracked cases for a short period, and covered a relatively small population.

Zhejiang is a populous and relatively affluent province located in the eastern China. The province has set up an Internet-based Comprehensive Chronic Disease Surveillance System (ICDSS) in 2001 for non-communicable diseases, including CVDs. The ICDSS covers a representative sample of 16.7 million residents (or 35% of the total population) in the province [14]. It operates based on an adapted framework of the MONICA project. The surveillance system creates a pool that linking databases from different sources to comprehensively investigate the epidemic of acute CVD events in the province. Using data collected from ICDSS, the study aimed to investigate the incidence, mortality and case-fatality of acute CVD events in Zhejiang in 2012, and in particular to examine the urban-rural differences.

A total of 16.7 million people (35% of the total population in the province) were monitored in the surveillance sites. The population under surveillance had similar demographic distributions to the provincial population (Table 1). The distribution of gender, residence and age were similar (p>0.05) in the surveillance population compared with provincial or national population.

In 2012, 61,279 acute CVD events were reported, including 9,866 (16%) CHD events and 51,413 (84%) stroke events (Table 2). Acute myocardial infarction, accounting for 56.8% of CHDs, and ischaemic stroke, accounting for 74.2% of strokes, were the two dominant subtypes. In addition, acute myocardial infarction was the most commonly reported CHD among all age groups, while the proportion of ischamemic stroke was higher than haemorrhagic stroke among those older than 35 years.

The incidence, mortality and case-fatality rates of all acute CVD events were respectively 367.0 and 127.1 per 100,000, and 34.6% (Table 3). CHD had an incidence of 59.1 per 100,000, a mortality rate of 43.3 per 100,000 and a case-fatality rate of 73.2%. Regarding stroke, we observed the incidence of 307.9, mortality of 83.8 per 100,000, and a case-fatality rate of 27.2%. Compared with females, males had higher incidence and mortality, but slightly lower case-fatality rates for CHD, stroke and total acute CVD events (p<0.001). Compared with their rural peers, urban residents reported higher CHD incidence and mortality, but lower case-fatality rates (p<0.001). Regarding stroke and total acute CVD, urban residents reported lower incidence, but higher mortality and case-fatality rates than rural residents (p<0.001). Incidence and mortality of acute CVD events increased as age advanced.

Table 4 shows that age and gender distributed evenly between the urban and rural areas in Zhejiang (p>0.05). No significant differences regarding all the rates were found between urban and rural areas among those aged below 35 years old (Table 5). For those aged 35 years and older, urban residents had higher CHD incidence, but lower stroke incidence (P<0.001) compared with rural residents. In addition, urban residents reported higher mortality for CHD and stroke than rural residents (P<0.001). However, rural residents had higher case-fatality rates on CHD compared with urban peers (P<0.01).

To our knowledge, this is the first study in China reporting population-based, real-time surveillance data on acute CVD events. ICDSS achieved a high level of completeness in reporting as the surveillance system obtained data directly from various sources. It also maintained a high level of validity and accuracy through ongoing and systematic quality assurance measures conducted in hospitals and CDCs. The procedures of ICDSS is similar to that of the US National Cardiovascular Disease Surveillance System [11] and the Cardio-cerebrovascular Disease Registration System in Takashima county, Japan [21].

The incidence, mortality and case-fatality rates of total acute CVD events were respectively 367.0 (CHD 59.1, stroke 307.9), 127.1 per 100,000 (CHD 43.3, stroke 83.8) and 34.6% (CHD 73.2%, stroke 27.2%) in Zhejiang in 2012. Mortality of CHD and stroke in Zhejiang are lower than China’s estimated national average (CHD, urban 86.3, rural 69.2 per 100,000; stroke, urban 125.1, rural 145.7 per 100,000) [7]. China does not have available data on national CVD incidence to be compared with [5]. The National CDC has started collecting CVD incidents from 302 counties since 2014, but robust data can only be reported after the system has been operated after several years. At the regional level, stroke incidence in our study was lower than that reported in the northeast provinces (i.e., 486 per 100,000) [22]. Our results were consistent with other studies that reported lower CVD incidence in south compared with the north in China [7, 19, 23]. These regional divergences may be related to China’s huge north-south variations in environmental, socioeconomic and behavioral factors. Zhejiang’s case-fatality rates of CHD and stroke were higher than urban districts of Beijing (53.6% and 17.3%) [24, 25].

Zhejiang had lower mortality for CHD but higher mortality for stroke compared with US and UK populations (standardized mortality rate of CHD: US 80.5, UK 68.8 per 100,000; stroke: US 25.4, UK 36.9 per 100,000) [2]. In addition, Zhejiang had lower incidence for CHD [26, 27], but higher incidence for stroke [28, 29] compared with UK and US. One plausible explanation may be that compared with western countries, China had lower prevalence of blood lipid abnormalities [30], the most important risk factors for CHD [31–33]. On the other hand, China had higher hypertension prevalence [22, 34], and higher smoking rates [35–37]. The case-fatality rates of CHD and stroke were higher in Zhejiang than those of western countries [34, 38]. This may be explained by China’s lack of stroke first-aid services, timely access to hospitals and adequate health insurance coverage for emergencies and inpatient services [16, 39].

In Zhejiang, CHD incidence and mortality were higher in urban areas than rural areas, which is probably due to the relatively higher prevalence of lipid abnormalities in urban areas [7]. We found that those aged 65 years or older presented the largest difference regarding CHD incidence and mortality between urban and rural areas. Currently in China, lipid profile examination is provided free for rural areas, but not for urban areas [40]. Our study suggested including lipid profile in the annual physical examination for urban residents. On the other hand, we found urban areas had a significantly lower CHD case-fatality rate than rural areas. In addition, we also found urban residents had lower stroke incidence, which echoed other studies [7, 41]. This may be due to a higher prevalence of hypertension and smoking in rural areas [42–45]. Furthermore, we found that the largest differences were found among the elderly. All these results implied that stroke prevention and management in rural areas was even more urgently needed compared with rural areas. Further research will be needed to explore why in our study the stroke fatality in the urban area was higher than that in the rural areas in Zhejiang, as other studies report otherwise in both China and elsewhere [7, 41, 46].

Based on a relatively complete and reliable CVD surveillance system, we found that incidence and mortality of acute CVD were lower in Zhejiang province compared with the national average. Within the province, we found a significant urban and rural difference. Special attentions need to be given to stroke control, especially in rural areas.