hlamydia, a sexually transmitted infection caused by the bacterium Chlamydia trachomatis, is the most commonly reported nationally notifiable disease. A total of 1,244,180 cases were reported in 2009. However, many infections are not detected, and an estimated 2.8 million infections occur each year. The burden of infection is greatest among sexually active adolescents and young adults; chlamydia prevalence among sexually active persons aged 14--24 years is nearly three times the prevalence among those aged 25--39 years (National Health and Nutrition Examination Survey 1999-2008 [NHANES], unpublished data, 2011). Substantial racial/ethnic disparities in chlamydial infection exist, with prevalence among non-Hispanic blacks approximately five times the prevalence among non-Hispanic whites. Among sexually active females aged 14--19 years, chlamydia prevalence is 6.8% overall (4.4% among non-Hispanic whites and 16.2% among non-Hispanic blacks).