Transmission Patterns of Chlamydia and Gonorrhea in Men Who Have Sex With Men

Chlamydia trachomatis bacteria, illustration
Chlamydia trachomatis bacteria. Computer illustration showing an inclusion composed of a group of chlamydia reticulate bodies (intracellular multiplying stage, small red spheres) near the nucleus (purple) of a cell. Chlamydia trachomatis causes a sexually transmitted infection that can go undetected causing infertility. It also causes the eye disease trachoma, which can lead to blindness.
Researchers conducted a study that compared the prevalence of single vs multisite Chlamydia trachomatis or Neisseria gonorrhea infections among men who have sex with men.

Chlamydial and gonorrheal infections were found to have distinctly different modes of transmission in men who have sex with men (MSM), according to results of a retrospective study published in Sexually Transmitted Infections.

Between 2018 and 2019, investigators analyzed data from MSM aged 16 years and older who were evaluated for Neisseria gonorrhea (NG) and Chlamydia trachomatis (CT) infections at the oropharynx, anorectum, and urethra via nucleic acid amplification testing (NAAT) at the Melbourne Sexual Health Centre in Australia. Patients who reported sexual contact with a woman in the past 12 months were excluded. The investigators sought to compare the prevalence of CT and NG infections by anatomical site, as well as the proportion of single vs multisite infections.

Among a total of 3938 patients included in the final analysis, the mean age was 27 (IQR, 24-32) years, 12.6% and 11.4% tested positive for CT infection and NG infection at any site, respectively, and 4.2% tested positive for both CT and NG infections at any anatomical site.

Among patients who tested positive for CT infection, 80.3% had single site and 19.7% had multisite infections. Similar findings were observed among patients who tested positive for NG infection, as 57.3% were single-site infections (95% CI, 52.6-61.7; P <.001) and 42.7% were multisite infections (95% CI, 38.2-47.3; P <.001). Of note, no significant differences in patients’ demographics or sexual practices were observed between MSM who tested positive for either CT or NG infection.

After stratification by infection location, 61.5% and 12.0% of CT and NG infections were found to have occurred at the urethra, respectively (P <.001). Anorectal infections occurred as multisite infections for 24.9% of CT infections compared with 59.5% of NG infections (P <.001). Among patients with multisite CT infection, the oropharynx was the most commonly infected site (66.7%) and the anorectum was the least commonly infected site (24.9%). Among those with multisite NG infections, the urethra was the most commonly infected site (88%) and the oropharynx was the least commonly infected site (52.5%).

The investigators found that the proportion of patients with any oropharyngeal infection was significantly decreased among those with CT vs those with GN infections (2.2% vs 6.6%; P <.001). Of note, no patient had a CT infection in both the urethra and oropharynx. In addition, the proportion of single-site infections that occurred at any site was significantly increased among patients with CT infection vs those with NG infection (P <.001).

This study was limited by selection bias due to its single-center setting, and its inclusion of NAAT assays that have not been validated for anorectal or oropharyngeal infections.

“The substantially [increased] rate of isolated urethral infection for chlamydia suggests that the urethra is the primary site for chlamydia transmission to the oropharynx or anorectum when men have sex with men,” the researchers concluded.


Tabesh M, Fairley CK, Hocking JS, et al. Comparison of the patterns of chlamydia and gonorrhoea at the oropharynx, anorectum and urethra among men who have sex with men. Sex Transm Infect. Published online January 12, 2021. doi:10.1136/sextrans-2020-054632