Chlamydia rates in public clinics: repeat infections exceed new diagnoses. (Digests).

Repeat infection with chlamydia appears to be a substantial problem among clients of public sexually transmitted disease (STD) clinics, and continued exposure to the same infected partner may be a key factor, according to analyses of data from a Denver clinic. (1) Among men and women who had at least two chlamydia tests, those who were infected at the time of their first visit had a significantly higher rate of infection at a subsequent visit than those who initially tested negative (23.6 vs. 10.0 infections per 100 person-years). In multivariate analyses, the risk of repeat infection was not associated with the acquisition of new partners, but was increased among clients who reported at their first visit that they never used condoms (odds ratio, 1.7).

The study included 3,568 men and women who had two or more chlamydia tests at least 30 days apart between January 1997 and June 1999 at a large public STD clinic. Using the clinic's database, researchers gathered information on clients' demographic characteristics, risk behaviors, clinical and laboratory findings, and treatment. For each client, they created a record based on data from the first visit that included a laboratory test for chlamydia and from the next visit at which an infection was diagnosed (or, for those who tested negative at all subsequent visits, the last visit during the study period). They categorized incident infections (i.e., those occurring between tests) as new if the client had initially tested negative or as repeat if the initial test had detected chlamydia infection.

Members of the study cohort were, on average, about 30 years old; most (59%) were male. Some 38% were black, 32% white, 27% Hispanic and 4% members of other racial or ethnic groups. The follow-up interval averaged 335 days.

Fourteen percent of clients tested positive for chlamydia at their first visit, and 11% tested positive at a subsequent visit. About two-thirds of each group received treatment before their laboratory results confirmed a diagnosis of chlamydia--either because they had clinical signs of infection (nongonococcal urethritis or epididymitis in men; mucopurulent cervicitis or pelvic inflammatory disease in women; or gonorrhea in either) or because they had a partner with suspected or confirmed chlamydia infection. While the proportion of clients treated because of clinical diagnosis was essentially the same for those with baseline and incident infections (54% and 58%, respectively), clients with incident infections were significantly less likely than those who tested positive at baseline to be treated because of their partner's known or suspected condition (13% vs. 23%).

In all, 11.7 incident infections occurred per 100 person-years of follow-up. The rate was significantly higher among clients with a repeat infection (23.6 per 100 person-years) than among those who were newly infected (10.0 per 100); repeat infections accounted for about one-quarter of all incident cases of chlamydia. Results of logistic regression analyses showed that a different set of risk factors predicted the incidence of new and repeat infections.

The odds of new infection were significantly higher among men than among women (odds ratio, 1.5) and were higher among blacks than among whites (1.8). Compared with people aged 30 and older, younger men and women had a sharply higher risk of new infection: Odds ratios increased steadily from 2.5 among those in their late 20s to 6.8 among teenagers. A history of STDs was associated with a doubling of the odds of new infection (1.8), as was inconsistent condom use (2.2). Finally, clients who reported at their follow-up visit that they had a new partner and did not use condoms had a higher risk of new infection than those who said either that they did not have a new partner or that they had a new partner but they used condoms at least some of the time (1.9).

Age was associated with the incidence of repeat infection as well, but the effect was not as strong as it was for new infection: Men and women in their late 20s had no greater risk than those aged 30 or older, and the odds of repeat infection were roughly doubled for both clients in their early 20s and teenagers (odds ratio, 2.2 for each group). Only two other factors were predictive of the incidence of repeat infection: Clients who had said at their first visit that they never used condoms had a higher risk than those who had reported any condom use (1.7), and clients who had received treatment at their initial visit because their partner had chlamydia or a related condition had a lower risk than those who had not (0.5).

While the researchers acknowledge that they were not able to determine whether repeat infections resulted from continued exposure to the same untreated partner or from contact with new partners, they contend that the multivariate results suggest "a pattern of unprotected intercourse with the source partner continuing after the first infection and thus increasing the risk for repeat infection." Therefore, they conclude that their findings "point to the need for the establishment and evaluation of partner services for persons with identified chlamydial infection."

REFERENCE

(1.) Rietmeijer CA et al., Incidence and repeat infection rates of Chlamydia trachomatis among male and female patients in an STD clinic: implications for screening and rescreening, Sexually Transmitted Diseases, 2002, 29(2): 65-72.