CHLAMYDIA POSITIVITY VERSUS PREVALENCE - WHATS THE DIFFERENCE

Background: Data on chlamydia screening collected as part of Regional Infertility Prevention Projects often do not include personal identifi ers, therefore repeat tests for patients during a year cannot be ident ified. Consequently, positivity is calculated and used to monitor chla mydia prevalence. Goals: To assess how well positivity can estimate pr evalence in family planning and sexually transmitted disease (STD) cli nic settings. Study Design: Analyzed data from chlamydia screening pro grams in three geographic areas of the United States that used unique patient identifiers. Results: The relationship between positivity and prevalence is related to both the percentage of tests that are repeat tests and the percentage of repeat tests that are positive. On average , the percentage of positive repeat tests was the same as or higher th an prevalence in family planning clinics; thus, positivity was the sam e as or higher than prevalence, In STD clinics, the percentage of posi tive repeat tests was consistently lower than prevalence; thus, positi vity underestimated prevalence, However, the absolute difference betwe en positivity and prevalence was less than 0.5% in family planning and STD clinics. Conclusions: Positivity can be used to monitor chlamydia prevalence in women screened in family planning and STD clinic settin gs.