Each year, diarrheal diseases kill at least 5 million children before they reach their fifth birthday. For the most part, poor countries bear the brunt of this burden. In many developing nations, it is usual for children to experience three or more serious episodes of diarrhea every year.¹ In countries that are not poor, diarrhea remains a neglected but substantial problem, lurking in deprived, diseased, and institutionalized populations. In the United States, diarrhea remains one of the common reasons for the admission of children to hospitals. The elderly, especially in nursing homes, have high rates of diarrhea; its resulting morbidity . . .