Background Chlamydia is the most commonly reported notifiable disease in the US, with over 1.2 million cases reported in 2009 (409.2 per 100 000 population). While rates based on case reports have been climbing steadily over the past 20 years (155% increase), interpretation of trends is difficult due to better disease detection, reporting, and screening coverage among sexually active women aged 15–24 years. Prevalence data from other sources may be more reflective of national morbidity trends.
Methods Chlamydia trends were analysed using data from three alternative sources. Using data from the National Health and Nutrition Examination Survey (NHANES), chlamydia prevalence from 1999 to 2006 was assessed in a nationally representative sample of the US population aged 14–39. Using data from the Infertility Prevention Project (IPP), two analyses of chlamydia positivity trends in different populations were conducted. The first analysis modelled trends among women aged 15–24 years tested in family planning clinics from 2004 to 2008; the second evaluated women aged 15–24 years who were tested in prenatal clinics from 2004 to 2009. Finally, data collected through the National Job Training Program (NJTP) on trends from 2003 to 2007 among high-risk men and women aged 16–24 years, were modelled. Models (IPP and NJTP analyses) controlled for age, race, geography, and test technology.
Results Based on analyses of data from each of these populations, chlamydia prevalence trends were flat or decreasing. In NHANES, prevalence declined 48% (95% CI: 23% to 72%), from 2.6% (95% CI: 1.9% to 3.5%) in 1999–2000 to 1.4% (95% CI: 0.9% to 2.0%) in 2005–2006. In IPP prenatal clinics, chlamydia positivity also decreased; the adjusted odds of having a positive chlamydia test declined by 35% from 2004 to 2009. Likewise, in the NJTP, the odds of a positive test decreased by 19% in women and 8% in men from 2003 to 2007. In IPP family planning clinics, positivity neither increased nor decreased from 2004 to 2008.
Conclusions Although rates of chlamydia based on case reports are increasing, analyses of prevalence data suggest that the overall prevalence of chlamydia may be decreasing. Reported chlamydia case rates are likely reflections of policy and programmatic changes and do not accurately reflect morbidity trends.
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