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INTRODUCTION
Acute gastroenteritis is an important public health issue worldwide [1-4]. In developed countries, while mortality is low, the associated morbidity remains high [5-8]. In order to better estimate the true level of morbidity in the community, several countries have conducted population-based studies [9-22]. Using prospective and retrospective methodologies, these studies have collected self-reported information from random samples of their target populations, including information on gastrointestinal symptoms (vomiting and diarrhoea) and their severity, secondary symptoms, pre-existing conditions, health-care use and burden, possible causes, and demographics. In these studies, gastroenteritis refers to the acute onset of enteric symptoms unrelated to existing health conditions, medication use, or other non-infectious causes, and is defined by its clinical picture, with symptom-based case definitions used to classify individuals as cases or non-cases. These case definitions are designed and used to estimate total morbidity, not as part of ongoing public health surveillance of enteric disease.
Comparing the results of such studies is complicated because both the terms used for the illness and the symptom-based case definitions vary, despite the fact that the studies are essentially evaluating the same phenomenon. This problem, although widely noted in the literature [1, 10, 12, 15, 16, 19, 20-22] has only been explored in a preliminary fashion using data from one country [23, 24]. Ultimately, a common, validated case definition and common set of reported results are needed to ensure comparability across population-based studies of gastroenteritis and to provide a credible estimate of the global burden of disease.
The current lack of a standard definition is due, in part, to the subjectivity of gastroenteritis as a syndrome. Additionally, it stems from the need for individual studies to be able to tailor their case definition to their specific purposes (e.g. diarrhoeal disease vs. acute gastrointestinal illness), to make their case definition and thus their data consistent with other previously collected data within their country, and to work within existing administrative, research, or other frameworks. Most studies already collect data in a manner which would allow more than one symptom-based case definition to be applied post hoc, although not all studies have collected all specific data items which could be important. Future studies could easily adapt data collection to enable the application of any study-specific case...