Seroepidemiology of chlamydia in Costa Rica.
A population-based study of the sero-epidemiology of chlamydia was performed among a nationally representative sample of 760 Costa Rican women aged 25 to 59 years. Interviews and sera collection were completed between September 1984 and February 1985. The overall seroprevalence of chlamydial antibodies among these women was 56.1%. Women 25 to 39 years of age had a seroprevalence of 51.1%, while women 40 to 59 years of age had a seroprevalence of 64.2%. Women who reported no prior sexual activity had a seroprevalence rate of 48.6%, compared with a seroprevalence rate of 80.7% among women who reported three or more lifetime sexual partners. The geometric mean titre (GMT) of seropositive women ranged from 34.4 among the women who reported no prior sexual activity to 155.0 among the women with three or more lifetime sexual partners. Sero-positivity was more consistently associated with sexual activity than with age. Women with serological evidence of past Herpes simplex virus type 2 (HSV-2) or syphilis infection were more likely to be seropositive than were women without evidence of exposure to these sexually transmitted diseases, even when controlled for age and the number of lifetime sexual partners. The seropositivity among never sexually active women indicates the probable presence of Chlamydia pneumoniae infections, while the high seroprevalence of chlamydial antibodies among the sexually active women suggests that sexually transmitted Chlamydia trachomatis infections represent a public health problem not previously quantified in Costa Rica. Further seroepidemiological and/or culture studies are warranted to determine the incidence and prevalence of sexually transmitted chlamydial infection among men and younger women.