O15.3 - Do we understand rectal chlamydia infections in women? A study including different anatomical sites, quantification and viability of Chlamydia trachomatis in two Swedish STI-clinics

Background

The understanding of rectal chlamydia infections in women is limited. Recent studies report an unexpectedly high prevalence of rectal chlamydia even among those declining having had anal sex. In those studies, vaginal and anal swabs were taken by the participants, which could imply contamination.

This study investigated the prevalence of cervical and rectal chlamydia among women attending two Swedish STI-clinics during 2019-2022. The aim was to compare sexual practice in relation to rectal chlamydia, including bacterial concentration and viability.

Methods

Women with an assumed high risk of chlamydia were asked to participate. Cervical, anal and rectal samples were collected for each patient. A proctoscope for children was used for rectal sampling to avoid contamination from the vaginal and perineal area. Attendees answered a questionnaire including experience of receptive anal sex.

Chlamydia trachomatis (CT) was detected by the Abbott Alinity-m STI system. Chlamydia DNA-concentration was determined using droplet digital PCR and viability assessed in the same system using a PCR-inhibiting dye.

Results

Of 313 women enrolled, 55 patients tested positive for anogenital chlamydia, of which 35 (63%) presented with concurrent rectal and cervical infection. Women testing cervical positive and rectal negative added up to 15 patients, whilst there were only two women testing rectal positive and cervical negative. Out of 15 negative rectal samples the corresponding anal sample tested positive for 7 (46%) patients.

Out of 38 patients testing positive for rectal chlamydia, only 15 (40%) reported anal sex in the past 12 months, and 12 of those 15 (80%) had experienced unprotected anal sex.

The CT concentration in rectal samples was similar in patients reporting anal sex and patients stating no anal sex. The overall viability was assessed to be 40% in cervical CT positive samples, but 30% in rectal CT positive samples.

Conclusion

The high proportion of cases with anal positive but rectal negative (46%) samples indicate urogenital contamination. This is supported by the finding that 60% of rectal positive patients stating no anal sex. Furthermore, our findings suggest that the viability and DNA-concentration was lower in rectal samples compared to cervical samples.