Globally diarrhoeal disease is one of the most important causes of childhood mortality and inadequate water and sanitation services are thought to be responsible for a major proportion of that disease burden. Even in developed countries contaminated water is a frequent cause of diarrhoeal disease. Various epidemiological and quantitative risk approaches have been used to estimate the actual burden of disease but these have given often very different estimates. This paper will review some of the complexities around the epidemiology of diarrhoeal disease that make disease burden estimates particularly complex for diarrhoeal disease. These include:

1. Multiple transmission pathways. For most waterborne enteric pathogens, water is not the only transmission pathway and it is plausible that reducing the proportion of disease due to one pathway (waterborne exposure) would not reduce total disease burden because of other pathways of infection.

2. Prior immunity. Like many infectious diseases, infectious enteric infections generate immunity in the host. Although unlike the case with many other infections the duration of immunity may not last long (maybe only 6 to 12 months).

3. Age specific effects. Studies have reported very different epidemiology in young children compared to older children and adults. Diarrhoea certainly can have very different outcomes in the different age groups.

4. Recall bias in studies of self-reported diarrhoea may over-estimate disease burden in some and under-estimate in other contexts.

This paper will consider these and other potential sources of bias and attempt to quantify their potential impact on disease burden estimates in a number of different contexts such as the reported health benefits from household water treatment and disease burden from recreational water exposure.

Keywords: Waterborne disease; Diarrhoea; Bias; Immunity

Biography: After graduating in Medicine from Manchester University Professor Hunter went onto specialise in Medicine Microbiology. He was Director of the Public Health laboratory, and Consultant in Communicable Disease Control in Chester until 2001 when he was appointed Professor of Health Protection in the Medical School at the University of East Anglia. Professor Hunter's early research focused on Candida infections particularly in the numerical analysis of strain typing data. More recently his research has been on the epidemiology of diarrhoeal disease especially that secondary to food and waterborne spread. He has undertaken case-controlled, and cohort studies, cross sectional surveys and randomised controlled trials in the UK, Europe, SE Asia, Africa and the Caribbean. He has also developed interests in Quantitative Microbial Risk Assessment and Meta-analysis. He has been an advisor to Food Standards Agency, Organization for Economic Cooperation and Development and the World Health Organization.