The organism Chlamydia trachomatis is an important sexually transmitted pathogen. Besides causing urethritis and cervicitis, it is known that this infection, if undiagnosed and untreated, may result in serious secondary complications and sequelae, increase the risk of HIV transmission and acquisition,^1–3 and may be a co-factor in the development of cervical cancer.⁴ The National STD Surveillance System was established in 1987 to monitor the sexually transmitted disease (STD) epidemic in China through STD case notification nationwide and prevalence surveys in a limited sentinel sites. In China, chlamydial infection was not reported as a separate notifiable STD until 2006.⁵ Laboratory based prevalence surveys have been gradually introduced into surveillance activities of chlamydial infections in China, and women at high risk—that is, female sex workers (FSWs), have been considered as one of key groups in such surveys. However, in implementation of these surveys, the settings where such high risk women are recruited vary widely from survey to survey. In order to explore possible differences in the prevalence of chlamydial infection between different settings, we measured the prevalence of chlamydial infection among women from the different settings.

The study population consisted of 1497 women, including 839 consecutive clients from …