Endemic giardiasis and day care.

Five surveys of 1,731 children for stool ova and parasites (1971 to 1981) in a rural county provide a unique perspective on naturally occurring, nonepidemic giardiasis. Currently white children in day care centers in Hampton County, South Carolina, experience attack rates of 26%. They enter the first grade with at least six times as much infection as those who do not attend day care. A trend toward more giardiasis linked to working mothers and day care is evident among white preschool children. This has not yet occurred among black preschool-aged children. These and other epidemiologic data indicate that as few as 100 children can maintain endemic levels of infection in a county of 18,000 residents. Person-to-person transmission in the day care setting is sufficient to explain this county's rising rate of stool positivity of infection (8% of all stool specimens submitted to the state laboratory).