The global burden of diarrhoeal disease in children

One in 12 of the children born in 2001 have died or will die before their fifth birthday. This represents an annual total of 10.8 million childhood deaths, about 70% of which occur in infancy. Child mortality has declined from an estimated 15 million deaths in 1980, but eminently preventable and treatable conditions, such as pneumonia, diarrhoea, malaria, measles, and malnutrition, are still leading killers of children. Aggressive efforts to reduce child mortality must continue. Hard data on the cause-specific disease burden will assist in planning interventions and measuring their impact. It is well known that diarrhoeal disease is one of the leading causes of illness and death in young children in developing countries. But how accurate are the morbidity and mortality estimates, and how can we improve them? In 1976, Rohde & Northrup estimated that annually diarrhoea killed up to 5 million children in developing countries, and urged the scientific community to "take science where the diarrhoea is" (1). Then Snyder & Merson analysed 24 longitudinal, prospective, community-based studies of diarrhoea published between 1954 and 1979 (2). They estimated that under-five-year-olds had 2.2 episodes of diarrhoea per year, resulting in 4.6 million deaths. In 1986, a committee of the US Institute of Medicine revised the diarrhoea mortality estimate to 3.5 million deaths per year, based on published data and field experience (3). Bern et al. then updated Snyder & Merson's analysis by using studies published from 1980 to 1990 (4). They documented diarrhoea morbidity of 2.6 episodes per child per year, a similar finding to that reported a decade earlier, but with lower mortality: 3.3 million deaths per year. Kosek et al. have recently made a further update by reviewing 60 studies of diarrhoea morbidity and mortality published from 1990 to 2000 (5). They conclude that diarrhoea accounts for 21% of all deaths at under five years of age and causes 2.5 million deaths per year, although diarrhoea morbidity remains relatively unchanged. However, an analysis conducted in 2000 by Murray et al. estimates that diarrhoea accounts for only 13% of all childhood deaths, amounting to 1.4 million deaths per year (6). These figures were based on information from national vital registration systems, sample registration systems, population laboratories, and epidemiological studies. Despite the different methods and sources of information, each successive review of the diarrhoea burden over the past three decades has demonstrated declining mortality but relatively stable morbidity. The decline in global diarrhoea mortality is confirmed by detailed information from monitoring in certain countries over time (7). Increased use of oral rehydration therapy, improved nutrition, increased breastfeeding, better supplemental feeding, female education, measles immunization, and improvements in hygiene and sanitation are believed to have contributed to this decline. Although few would disagree that there has been a decline in diarrhoea mortality, the wide range in current figures reflects the inherent uncertainty of these estimates. Earlier studies do not reflect the current situation and, in addition, cause of death was often ascertained by verbal autopsies, which have variable sensitivity and specificity. The WHO estimates were based on more recent vital registration data, but only countries from Latin America had registration coverage reaching 28%. Substantial extrapolation and modelling were needed to produce estimates for regions such as sub-Saharan Africa, with its estimated coverage of 0. …