Incidence and repeat infection rates of Chlamydia trachomatis among male and female patients in an STD clinic: implications for screening and rescreening.

Background: Nucleic acid amplification tests permit widespread screening for Chlamydia trachomatis. However, the public health benefit of screening may be reduced by high chlamydia incidence and repeat infection rates.

Goal: To study chlamydia incidence and repeat infection among clients of a sexually transmitted disease (STD) clinic.

Study Design: A retrospective cohort study of all clients tested for chlamydia on two or more occasions during a 30-month period.

Results: Between January 1, 1997 and June 30, 1999, 3568 clients were tested on multiple occasions. Of these, 491 (13.8%) had positive test results at their first visit (baseline infections), and 385 (10.8%) had positive results at a subsequent visit (incident infections). The overall incidence was 11.7 per 100 person-years of follow-up evaluation (95% CI, 10.6-12.9). The incidence was significantly higher among those 25 years of age or younger (19.7/100 person-years; 95% CI, 17.3-22.2) than among older subjects (6.8/100 person-years, 95% CI, 5.7-7.9; relative hazard, 3.0; 95% CI, 2.5-3.7). The incidence of new infections among persons without a baseline infection was 10.0 per 100 person-years (95% CI, 8.8-11.2), whereas the incidence of repeat infections was 23.6 per 100 person-years (95% CI, 18.9-28.2; relative hazard, 2.4; 95% CI, 1.9-3.0), with repeat infections accounting for 26% of all incident infections. In the multivariate analysis, the factors associated with new infections included young age, black race, male gender, history of sexually transmitted disease, a new sex partner in the previous 30 days, and inconsistent condom use. The factors associated with repeat infection were younger age, nonuse of condoms, and no treatment after contact with a partner who had a diagnosis of chlamydia or a chlamydia-related condition, as measured at the initial visit.

Conclusions: Among clients making multiple visits to the clinic, repeat infection rates were significantly higher than new infection rates, likely because of reexposure to untreated partners. These findings point to the need for more effective strategies to prevent chlamydia infection, including enhanced partner management services and rescreening.