Fig. 2.

Recruitment of reported laboratory-confirmed Giardia cases and matched controls in the Colorado and Minnesota giardiasis case-control study. A total of 213 case-patients were enrolled, of which 199 were matched with controls. The 440 case-patients not enrolled were most commonly excluded from enrollment because they had onset of gastrointestinal symptoms greater than 6 weeks (43.6%), refused to participate (12.7%), were recent immigrants, adoptees, or refugees (12.3%), or were asymptomatic (9.3%). Other reasons for non-enrollment included inability to be reached (7.3%), non-English speaking (6.6%), failure to have the earliest illness onset within a family cluster of laboratory-confirmed giardiasis (2.3%), incomplete interview (0.5%) and other miscellaneous reasons (5.5%).