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Chlamydia trachomatis (Ct) and human papilloma virus (HPV) are common infections in sexually active young women. The risk factors for acquiring each of these sexually transmitted infections (STIs) are similar. Although each infection causes a distinct disease entity, the consequences of having Ct infection in the context of HPV infection may be even more significant. Specifically, Ct infection may increase a woman's risk of cervical dysplasia, which could progress to cervical cancer.
Does chlamydial infection increase the risk of cervical dysplasia, otherwise known as cervical intraepithelial neoplasia (CIN)? On the surface, this research question seems straightforward. In reality, addressing this question is complex and requires careful consideration of the study population, study design and, importantly, the underlying theoretical causal model for the relationship. In this issue of Sexually Transmitted Infections, Lehtinen et al present an interesting and suggestive study of the relationship between chlamydial infection and CIN based on a retrospective cohort analysis of the placebo arms of the FUTURE (Females United to Unilaterally Reduce Endo/ Ectocervical Disease) trials.1 This secondary analysis is not the first to suggest an association between chlamydial infection and CIN and/or cervical cancer.2–7 But each of these studies, like the Lehtinen et al study, has significant methodological issues, which cloud interpretation of the results. Using the placebo arms of the FUTURE trials is opportunistic, but this approach also has major limitations, including concerns regarding temporality, uncertainty of Ct infection status prior to enrolment, limited behavioural information and inconsistent results between Ct and high-grade dysplasia (CIN-2 …