Introduction In prior studies it is demonstrated that, in women, the prevalence of anorectal infections with Chlamydia trachomatis (CT) is comparable to genital CT. Yet, the clinical relevance and the role in overall transmission of anorectal CT in women is still under debate. The assessment of CT viability will gain new insight in current knowledge gaps. Recently, we validated the viability-PCR (V-PCR) method to assess CT viability in genital CT positive samples. In this study, V-PCR was utilised to assess CT viability in anorectal samples from CT positive women.

Methods COBAS 4800 CT/NG routine testing was used for CT diagnosis. Women positive for genital and/or anorectal CT (n=66), collected self-taken vaginal and anal swabs at our outpatient STI clinic (South Limburg Public Health Service) prior to treatment at the initial screening and at treatment consultation. V-PCR and culture were used to assess CT viability.

Results V-PCR results showed that in up to 31% (8/26) of anorectal positive samples less than 1% of the detected CT DNA originated from viable bacteria. However, in 62% (16/26) of anorectal positive samples more than 10% of the detected CT DNA originated from viable CT. In this category, routine COBAS results also showed a stable bacterial load between initial screening and treatment consultation, further supporting the presence of large amounts of viable CT. Finally, culture results confirmed results of V-PCR and showed a direct relation to the proportion of viable CT in clinical samples.

Conclusion Although the cohort was relatively small, results in this study showed that a substantial amount of anorectal CT positive samples contained viable CT. Overall, these results provide further evidence that anorectal CT infections in women are clinically relevant. In a currently ongoing larger cohort study, clinical samples from CT positive women (n=400) will be assessed for viability before and after treatment (FemCure Study).