Concordance of chlamydia infections of the rectum and urethra in same-sex male partnerships.

Background
Chlamydia remains one of the most common sexually transmissible infections in men who have sex with men (MSM) worldwide.

Aims
To describe the concordance of chlamydia infections of the rectum and urethra in MSM and their male partners. This data can then be used to inform mathematical models of chlamydia transmission in MSM.

Methods
This was a cross-sectional study of chlamydia diagnoses in MSM and their male sexual partners between 2011 and 2015.  Men who did not test for chlamydia at both the rectum and urethra were excluded from the analysis.

Results
Our study included 473 MSM partnerships (946 men). 30 men had urethral chlamydia, of whom 14 (47%, 95% CI 28 to 66) had a partner with rectal chlamydia. 46 men had rectal chlamydia, of whom 14 (30%, 95% CI 18 to 46) had a partner with urethral chlamydia.  The proportion of men with rectal chlamydia whose partner had urethral chlamydia detected was higher than the proportion of men with urethral chlamydia whose partner had rectal chlamydia (p = 0.02).

Conclusions
This is the first study of chlamydia concordance in male sexual partnerships and suggests that the efficiency of chlamydia transmission between men is lower than that reported between men and women, and also that the chlamydia transmission from the urethra to the rectum is more likely than transmission from the rectum to the urethra. 

Funding 
Funding for this project was, in part, supplied by a National Health and Medical Research Council (NHMRC) programme grant (No.: 568971). EPFC is supported by the Early Career Fellowships from the Australian NHMRC (No.: 1091226).

Concordance of chlamydia infections of the rectum and urethra in same-sex male partnerships: A cross-sectional analysis.