Nearly three-quarters of mothers with preschool-age children work outside the home. Two-thirds of their children currently receive either full- or part-time care in a child care center or family child care home and are thus at risk for acquired human cytomegalovirus (HCMV) infection. Although HCMV infection rarely causes symptoms of disease among infected children or adults, it is the most common cause of congenital viral infection in the world today. In the United States each year, 30,000 to 40,000 infants are born congenitally infected with HCMV. As many as 7,500 to 10,000 of these infants will be severely impaired with mental retardation, motor deficits or cerebral palsy, seizures, visual deficits or blindness, and sensorineural hearing loss. HCMV frequently infects children attending child care centers. Subsequently these children can transmit the virus to their parents or adult child care providers. This renewal proposal will extend current studies of the occupational risk of HCMV infection among women who have contact with young children. By monitoring seroconversion among adults and HCMV excretion among children, this study will determine whether the risk of HCMV infection differs for caregivers, children and parents who use small family child care arrangements with 6 or fewer children as compared to those who use large registered child care centers. At present, the risk of HCMV infection for the 2 million children currently in family child care, their parents or caregivers is not known. The epidemiology of HCMV transmission will be characterized by using PCR-based methods, and the phylogenetic relationships of HCMV will be established. This proposal will determine whether HCMV transmission within the child care center can be interrupted by institution of specific hygienic measures and whether these measures can be successfully implemented by child care center staff.