Specific pathogens can be identified in 55% to 85% of cases of diarrhea in infants, in sharp contrast to the 25% to 35% isolation rates of the 1960s. Microbiology, pathogenesis, and diagnosis are described for“summer diarrhea,”most often caused byE. coli, and viral diarrhea, usually caused by rotavirus. Other common pathogens include Shigella, Salmonella, Campylobacter, and Yersinia.