Selective screening for chlamydia in Wisconsin is based on locally-derived prevalence and risk factor data. Every 5-7 years since 1990, prevalence and risk factors have been evaluated to assure optimum effectiveness by enacting a period of "universal" screening in a selected subset of clinics, where a chlamydia test is offered to all patients who agree to participate and fill out a questionnaire. Behavioral and clinical risk factor data are then correlated with chlamydia positivity to determine the most effective screening strategies. Different "levels" of criteria may be adopted for different populations or geographical areas of the state.