Why Are Rates of Reported Chlamydia Changing in the United States? Insights From the National Job Training Program

In 2010 to 2017, rates of reported chlamydia decreased among young Black women but increased for White women and all men. Because chlamydia case rates can be influenced by changes in prevalence, screening, and other factors, we compared chlamydia prevalence trends in a sentinel population with national case rate trends to understand potential drivers of case rate trends.

Chlamydia prevalence was calculated annually among 16- to 24-year-old entrants to the National Job Training Program (NJTP) in 2010 to 2017. An expectation-maximization-based maximum likelihood approach was used to adjust for misclassification due to imperfect test sensitivity and specificity. Models were stratified by sex, age, and race/ethnicity. A statistically significant trend in prevalence was defined as nonoverlapping 95% confidence intervals comparing 2010 and 2017. Trends in chlamydia prevalence were compared with trends in case rates using percentage change over time; relative changes ≥10% were considered meaningful.

Among NJTP entrants in 2010 to 2017, chlamydia prevalence was stable for all Black women, whereas case rates decreased for adolescents (-12%) and were stable for 20- to 24-year-olds (-4%). Among adolescent White women, prevalence was stable, whereas case rates increased (+30%). For White women aged 20 to 24 years, prevalence increased +62% and case rates increased +43%. Trends in prevalence differed from trends in case rates for all subgroups of men.

Prevalence trends in this sentinel population differed from national case rate trends for Black women, White women, and men, suggesting potential decreased screening among Black women aged 16 to 19 years, increased prevalence among White women aged 20 to 24 years, and increased screening among men.