Introduction:
Chlamydia trachomatis is the most commonly diagnosed STI in the UK. While men-who-have sex-with-men are known to be at-risk of rectal chlamydia infection (ReCT), the prevalence in women is not well understood. This may have important implications for testing and treatment approaches since azithromycin and doxycycline are considered first-line regimens for uncomplicated urogenital infections, whereas doxycycline is the preferred treatment for ReCT. 

Objectives:
Undertake a systematic review to: 1) calculate ReCT positivity (number ReCT positive/number tested) among women in different testing settings; 2) determine the proportion of women diagnosed with ReCT with: a) concurrent urogenital infections and; b) a history of anal-intercourse.

Methods:
Medline, Embase, CINAHL, PsychINFO and the Cochrane Database were searched for articles published January 1997-September 2015. Studies reporting ReCT positivity in women aged ≥15 years in high-income countries were included and relevant data extracted. 

Results:
Eleven studies were included, all of which investigated women attending sexual health services. Populations tested varied e.g. 3/11 studies included only women with a history of anal-intercourse. Among all studies, ReCT positivity ranged from 2-77% (median 8%). Among women with ReCT, 41%-100% had a concurrent urogenital infection; 13%-100% reported anal-intercourse (where data were available).

Discussion:
ReCT infections have been found in a substantial proportion of women in the populations tested. In these studies, urogenital testing alone would have missed up to 31% of chlamydia infections. Further work to establish need, criteria and feasibility for routine ReCT testing in women is needed to ensure chlamydia infections are not missed or inadequately treated.

How Common is Rectal Chlamydia trachomatis Infection in Women? A Systematic Review, 1997 to 2015.