ObjectivesHigh-risk human papillomavirus (hrHPV) is the primary cause of cervical cancer. As Chlamydia trachomatis is also linked to cervical cancer, its role as a potential co-factor in the development of cervical intraepithelial neoplasia (CIN) grade 2 or higher was examined.MethodsThe placebo arms of two large, multinational, clinical trials of an HPV6/11/16/18 vaccine were combined. A total of 8441 healthy women aged 15–26 years underwent cervicovaginal cytology (Papanicolaou (Pap) testing) sampling and C trachomatis testing at day 1 and every 12 months thereafter for up to 4 years. Protocol-specified guidelines were used to triage participants with Pap abnormalities to colposcopy and definitive therapy. The main outcome measured was CIN.ResultsAt baseline, 2629 (31.1%) tested positive for hrHPV DNA and 354 (4.2%) tested positive for C trachomatis. Among those with HPV16/18 infection (n=965; 11.4%) or without HPV16/18 infection (n=7382, 87.5%), the hazard ratios (HRs) associated with development of any CIN grade 2 according to baseline C trachomatis status were 1.82 (95% CI: 1.06 to 3.14) and 1.74 (95% CI 1.05 to 2.90), respectively. The results were comparable when only the 12 most common hrHPV infections were considered, but the excess risk disappeared when the outcome was expanded to include CIN grade 3 or worse.ConclusionFurther studies based on larger cohorts with longitudinal follow-up in relation to the C trachomatis acquisition and a thorough evaluation of temporal relationships of infections with hrHPV types, C trachomatis and cervical neoplasia are needed to demonstrate whether and how in some situations C trachomatis sets the stage for cervical carcinogenesis.Trial registrationNCT00092521 and NCT00092534.

Only a few population-based serological studies have been undertaken on C trachomatis epidemiology over time. In Finland the seroprevalence of C trachomatis is decreasing all over the country, albeit with small clusters remaining.

Background: Reported rates of Chlamydia trachomatis are on the rise contradicting the declining rates of C. trachomatis associated reproductive sequelae in Western countries. Population based evaluation of the real trend of C. trachomatis infection is important to contemplate prevention efforts. We studied C. trachomatis occurrence during the past 20 years in Finland comparing incidence rate data based on serology and reported C. trachomatis laboratory notifications.