Is it possible to predict which diarrhoea episodes will lead to life-threatening dehydration?

Early detection of children who are likely to develop life-threatening dehydration as a consequence of diarrhoea would be of great value for health care workers in developing countries. We carried out a case-control study to compare the symptoms and signs observed on the first day of diarrhoea in two groups of 192 children aged under two years, in the Brazilian city of Porto Alegre. The cases were children admitted to a hospital with moderate or severe dehydration, and controls were children from the same neighbourhoods as the cases, who had diarrhoea which did not lead to hospital admission. The sensitivity and specificity of different clinical indicators were calculated. Alterations in thirst (82%), followed by six or more stools (71%), fever (60%), vomiting (58%) and loss of appetite (57%) had the highest sensitivities, whereas the specificities were largest for blood in the stools (97%), fever (78%) and vomiting (78%). Assuming that dehydration occurs in 5% of all episodes of diarrhoea, the use of fever as a screening criterion, or the use of vomiting, would select 24% of all children with diarrhoea, and capture about 60% of all episodes of dehydration. The combination of fever or vomiting would increase the proportion selected to 36%, and capture 75% of episodes of dehydration.