Giardia prevalence among 1-to-3-year-old children in two Washington State counties.

A survey of intestinal parasites was conducted in two Washington counties. Giardia prevalence among 518 children surveyed was 7.1 per cent and was unrelated to the source of domestic drinking water (surface or well), day care center attendance, or parental occupation. Identified risk factors for Giardia infection include a history of drinking untreated surface water and having two or more siblings between the ages of 3 and 10 years. Of 47 family members of Giardia positive children, 10 (21.3 per cent) were Giardia positive.