Diarrhea is a major killer of children, with an estimated 800,000 deaths each year; it has many causes, and doctors want to focus on the most common ones to bring death rates down.
The study, financed by the Bill and Melinda Gates Foundation and published by The Lancet, found that the most common causes were rotavirus; a protozoan called Cryptosporidium; and two bacteria, Shigella and a toxin-producing strain of E. coli. In some areas, other pathogens, including the bacteria that causes cholera, were also important.
The study followed more than 9,000 children with diarrhea seen at clinics in Bangladesh, Gambia, India, Kenya, Mali, Mozambique and Pakistan, and, for comparison, more than 13,000 children without the disease. The children with diarrhea were more likely to have stunted growth and eight times as likely to die during a two-month follow-up period.
Diarrhea seemed to be linked to chronic malnutrition, which causes gut inflammation that can make it harder to digest food.
The prominent role of Cryptosporidium came as a surprise to the authors; it had been best known as a killer of adults whose immune systems were suppressed by AIDS.
In an editorial accompanying the study, other experts said rotavirus vaccine could save many lives.