Chlamydia positivity versus prevalence. What's the difference?
BACKGROUND
Data on chlamydia screening collected as part of Regional Infertility Prevention Projects often do not include personal identifiers, therefore repeat tests for patients during a year cannot be identified. Consequently, positivity is calculated and used to monitor chlamydia prevalence.


OBJECTIVE
To assess how well positivity can estimate prevalence in family planning and sexually transmitted disease (STD) clinic settings.


METHODS
Analyzed data from chlamydia screening programs 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 than prevalence in family planning clinics; thus, positivity was the same as or higher than prevalence. In STD clinics, the percentage of positive repeat tests was consistently lower than prevalence; thus, positivity underestimated prevalence. However, the absolute difference between 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 settings.
Dicker
L W
LW
Division of Sexually Transmitted Diseases Prevention, Centers for Disease Control and Prevention, Atlanta, Georgia 30333, USA.
Mosure
D J
DJ
Levine
W C
WC
D002690:Chlamydia Infections / Q000175:diagnosis / Q000453:epidemiology*; D002692:Chlamydia trachomatis; D005193:Family Planning Services; D005260:Female; D006801:Humans; D015995:Prevalence