Estimating the burden of acute gastrointestinal illness in the community in Gansu Province, northwest China, 2012–2013

Acute gastrointestinal illness (AGI) is a common illness all over the world. The aetiological factors of AGI include viruses, bacteria, parasites, toxins, and metals. The symptoms of AGI typically include diarrhoea and/or vomiting. In low and middle-income countries, this disease is one of the leading causes of morbidity and mortality, especially in children [1]. Even in industrialized countries, the social and economic burden caused by AGI were reported to be substantial due to its high morbidity, although its mortality is low in these countries [2–6]. The social and economic burden of AGI would be considered to be significant in China.

To estimate the burden of AGI to the society in China, the China National Center for Food Safety Risk Assessment (previously known as the Food Safety Section of the National Institute for Nutrition and Food Safety, Chinese Center for Disease Control and Prevention) conducted a population-based study to describe community situations of AGI in several provinces during 2010–2011 [7, 8]. However, systematic studies to investigate the burden of AGI in northwest China were still lacking. In this region, economic growth rates have lagged far behind those of other regions in China and their basic medical services need to be improved. Therefore, estimation of the burden caused by AGI within the population is of particular importance for better utilization of the limited medical services, and ultimately, for establishment of preventive strategies.

Reports from a number of countries suggest that rates of AGI in a community depend on person, place and time [9, 10]. In Gansu Province, as there are distinct regional differences in climate and environmental conditions, variable in AGI rates and situations, including social burden, were expected across the Province. Therefore, the objectives of the current study were to estimate the occurrence, distribution, and burden of self-reported AGI in Gansu Province located in northwest China.

This study provides the first population-based estimates of the occurrence, distribution, and burden of AGI in Gansu Province of northwest China. The results indicate that AGI leads to a substantial burden in this province. Based on the estimates of 1.16 AGI episodes per person-year and 73.8% of cases seeking medical care for AGI in this study, 29.6 million cases of AGI and 21.9 million medical consultations are estimated to occur each year in Gansu Province. The mean duration of illness was 2.5 days. If extrapolated to the population, 73.4 million days of illness due to AGI occur in the Gansu population each year.

We compared our results with the recently performed retrospective studies in other developing countries using compatible case definitions. The monthly prevalence of 8.5% in this study is higher than those reported for Jamaica (4.0%), Malaysia (5.0%), but lower than those reported for Chile (9.2%) and Cuba (10.6%) [9, 14–16]. The AGI prevalence estimated in the Gansu population is also higher than those reported for other regions of China [8, 17]. In the northwest parts of China, like many other developing regions in the world, people’s living standard is yet to be improved. Substandard hygiene and sewage disposal, inadequate facilities for food storage and preparation, and lack of appropriate drinking water are factors that may contribute to the high incidence rate of AGI in this region.

The methods for case ascertainment significantly impact incidence estimates. A UK study shows that the retrospective AGI study estimated 2–3 times higher incidence in the community than the prospective study [18]. This discrepancy was once attributed to telescoping, a recall bias leading respondents to attribute to the survey period episodes of AGI that occurred earlier. However, an evidence also exists that the shorter 7-day recall period yields significantly greater annual estimates compared to the longer 30-day recall period, which is contrary to telescoping resulting in the true burden of disease being underestimated [16, 19, 20]. Standardizing these methodological choices is important if valid estimates of the burden of AGI from different countries are sought.

Because it is not mandatory to report sporadic foodborne illnesses to a specific agency in China, the number on foodborne infection and intoxication cases do not accurately reflect, but tends to be lower than real cases. In 2012, only 397 foodborne disease cases were reported to the Gansu Provincial Foodborne Diseases Surveillance Network (data not shown). The total number of AGI in a study multiplied by the proportion of foodborne AGI gives the total number of cases of foodborne AGI in the region. Many of the foodborne AGI estimates in the developed countries are established using cause-specific estimates [21–23]. Without any pathogen attribution, such extrapolation is erroneous. Further research into the pathogen-specific burden of AGI is necessary to better estimate the burden of AGI and foodborne disease in this region.

When the cases of AGI with concurrent respiratory symptoms were excluded from the analysis, the incidence rate dropped to 1.04 AGI episodes per person-year, a reduction of 10.5%. This variation falls within the range of those reported by similar surveys conducted in the USA, Canada, Australia, and Italy [24, 25]. As some AGI cases with respiratory symptoms may be due to respiratory infections, it is necessary to consider this issue when estimating the burden of foodborne disease based on data from population studies.

The highest rate of disease in children aged 5–14 years is unique, as previous studies suggest highest rates of AGI among children aged 0–4 years [14, 16]. In the present study, the AGI prevalence was higher for young male groups. Young adults and males are more likely to engage in such food handling leading to higher risk than others, which may be due to the lack of food safety education/training, role models, and/or food-handling experience [26]. Additionally, this study found a higher rate of AGI in females aged >25 years, as in other studies [8, 27]. Having far higher occasions in handling food and caring for children may induce females more frequently exposed to enteric pathogens than males. Identification of groups of people vulnerable to AGI is useful to prioritize resource allocation. Food safety education should be started during childhood and should reach out to the mass of people.

There is a strong link between climate-related events, farming activities and the occurrence of AGI [10, 20, 28, 29]. Gansu Province is predominantly an agricultural area, which has complex landforms and multiple climate types. Baiyin is an industrial district and there was lower risk of AGI, which may be attributed to the absence of livestock and, consequently, their drinking water sources being less contaminated by agricultural run-off. The economic level is higher in Baiyin than in the other two sites, and the prevalence of AGI in Baiyin is close to those in some developed regions of China, such as Shanghai [8]. Liangzhou is located at the edge of dessert, and land desertification has caused many agricultural populations migrate to cities or other places, or to make a living in other means. The lower risk of AGI might be related to the reduced rainfall and the reduced farming activities. Qingcheng showed a significantly higher risk than in the other sites. The weather in Qingcheng is warm and humid, which is appropriate for intensive farming activities.

The proportion of cases reporting that consuming contaminated food (55.5%, 57/103) was a cause of their illness was higher than previous studies [8, 17, 30]. In fact, people seldom really know the cause of their AGI, although they usually attribute it to food. However, if there is no better way to estimate the proportion of foodborne AGI, this subjectively obtained proportion may be used to roughly estimate the burden of foodborne disease [8, 31]. Further research into the pathogen-specific burden of AGI is needed to estimate the foodborne proportion of AGI more accurately.

The proportions of cases who visited a doctor (73.8%) and who were hospitalized (21.2%) found in this study were higher than the proportions observed in other regions of China and in those countries cited above [8, 11, 17, 25, 32, 33]. These differences may reflect important differences in healthcare systems in the studied countries. However, the fact that a relatively high proportion of cases visited a doctor and hospitalized may also suggest that this study is primarily capturing the severe cases.

Of the respondents with AGI who visited a doctor, 50.5% provided a stool sample, which was higher than in other countries [11, 25, 32, 33]. If there are 21.9 million medical consultations each year in Gansu Province, the number of stool exam is 11.0 million. This provides a rich opportunity to document pathogen-specific illness rates. However, when a stool specimen is received, it is routinely tested for white blood cells but not cultured for pathogenic bacteria. Although clinical laboratories often performed tests of unproven value, the fact that the practice of seeking health care and submitting a stool sample is important. The proportion of seeking medical care for AGI and the proportion of stool sample submission will help to estimate the size of each layer in the surveillance pyramid for AGI.

Antibiotics are very rarely prescribed for the treatment of AGI. However, their use was reported by 65.6% of those with AGI, much higher than in other countries [9, 16, 25, 32, 34, 35]. However, proportion of antibiotic use in Gansu population was similar to those reported by other regions of China, except Hong Kong [8, 17]. If there are 29.6 million episodes of AGI each year in Gansu province, the number of AGI cases who are treated with antibiotics may be 19.4 million. This is of particular concern, particularly in view of the increase in antibiotic resistant pathogens and human susceptibility to ingested pathogens.

There was a tendency for Gansu population with higher household incomes to be more likely to report AGI, quite different from findings in Malaysia and Malta [15, 36], but similar to those in Australia and the United States [10, 37]. In a previous study carried out in other regions of China, the multivariate analysis showed that the variation across income groups was not significant [8]. This is possibly due to a reporting bias, with more wealthy households more likely to perceive that they have symptoms, pay more attention to hygienic conditions, or may be due to such behaviours in this group as eating out and travelling more frequently, leading them greater risk of acquiring AGI. Further research is needed to understand the relationship between household incomes and the occurrence of AGI in this region.

The response rate was quite high in this study compared to surveys in those countries cited above. This high rate may be attributed to: (1) a face-to-face interview employed to enable us to reach out to potential participants who do not have access to a telephone; and (2) the surveys carried out by trained health workers whom most people in Gansu Province regard highly.

We conclude that acute gastrointestinal illness (AGI) represents a substantial burden on health and economy in Gansu Province in northwest China. Ongoing research to identify the main causes of AGI is needed for more accurate estimate of the burden of AGI in this region.