Worldwide, gastrointestinal infections and diarrheal diseases result in significant morbidity and mortality with approximately four million deaths each year. The majority of infections occur in infants and children living in developing nations. Currently, the most common etiologic agents are the rotaviruses. More recently, the role for enteric adenoviruses, astroviruses, Norwalk virus and other caliciviruses in the pathogenesis of childhood diarrheal diseases has received further clarification. Branch investigators are evaluating the role of these viruses as causes of diarrhea in a population- based cohort of Egyptian children who were monitored for a period of three years. This information should help in the development of preventive measures against infection by these viruses, including the development and future evaluation of candidate vaccines. Laboratory analyses of specimens collected during the first year of observation have been completed. Results showed that rotavirus diarrhea incidence rates (episodes per person-year) were 0.13 for infants < 6 months, 0.61 for those 6-11 months, 0.17 for the 12-23 month age group, and 0.15 for those 24-35 months of age. Fifty-six percent of children with rotavirus diarrhea had clinical dehydration, and 90% of rotavirus diarrhea occurred from July- November. In infants < 1 year of age, receipt of breastmilk was associated with a lower incidence of rotavirus diarrhea. No other sociodemographic or environmental factor was found to be significantly associated with rotavirus diarrhea. Of the 46 rotavirus strains identified, 87% were typeable, and all were G serotypes 1 and 2. Hence, rotavirus diarrhea is a major cause of morbidity in this population. Promotion of breast- feeding may exert a protective effect in young infants in this setting, but measures to improve water and sanitation are unlikely to be effective preventive measures. Therefore, the use of effective immunization against rotavirus in early infancy should be considered a public health priority in this population. At this time, results from the laboratory evaluations for astrovirus and enteric adenovirus infections, as well as second and third year specimens are undergoing statistical analyses. - Viral gastroenteritis, rotavirus, astrovirus, Egypt, diarrhea, calicivirus - Human Subjects