Participants in the Giardia prevalence study among Bergen preschoolers, one year after the 2004 outbreak. The figure shows how children 1-5 years of age in Bergen were invited to join the study. Children were originally classified based on whether their residential address was supplied by Giardia-contaminated water. Those accepting were further classified according to the answers of the questionnaire.
Mellingen et al. BMC Public Health 2010 10:163 doi:10.1186/1471-2458-10-163