Anorectal Chlamydia trachomatis Load Is Similar in Men Who Have Sex with Men and Women Reporting Anal Sex

PLoS One. 2015 Aug 11;10(8):e0134991. doi: 10.1371/journal.pone.0134991. eCollection 2015.


Background: Anorectal Chlamydia trachomatis (chlamydia) is frequently diagnosed in men who have sex with men (MSM) and in women, but it is unknown whether these infections are comparable in clinical impact and transmission potential. Quantifying bacterial load and identifying determinants associated with high bacterial load could provide more insight.

Methods: We selected a convenience sample of MSM who reported anal sex (n = 90) and women with concurrent urogenital/anorectal chlamydia who reported anal sex (n = 51) or did not report anal sex (n = 61) from the South Limburg Public Health Service's STI unit. Bacterial load (Chlamydia/ml) was quantified for all samples and log transformed for analyses. Samples with an unquantifiable human leukocyte antigen (n = 9) were excluded from analyses, as they were deemed inadequately sampled.

Results: The mean log anorectal chlamydia load (3.50) was similar for MSM and women who reported having anal sex (3.80, P = 0.21). The anorectal chlamydia load was significantly higher in these groups than in women who did not report having anal sex (2.76, P = 0.001). Detectable load values ranged from 1.81-6.32 chlamydia/ml for MSM, 1.74-7.33 chlamydia/ml for women who reported having anal sex and 1.84-6.31 chlamydia/ml for women who did not report having anal sex. Symptoms and several other determinants were not associated with anorectal chlamydia load.

Conclusions: Women who did not report anal sex had lower anorectal loads, but they were within a similar range to the other two groups. Anorectal chlamydia load was comparable between MSM and women who reported anal sex, suggesting similar transmission potential.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Anal Canal / microbiology*
  • Bacterial Load
  • Chlamydia Infections / epidemiology*
  • Chlamydia Infections / microbiology*
  • Chlamydia trachomatis / genetics
  • Chlamydia trachomatis / isolation & purification*
  • Female
  • Homosexuality, Male*
  • Humans
  • Male
  • Middle Aged
  • Risk Factors
  • Sexual Behavior*
  • Young Adult

Grants and funding

This work was investigator initiated, and supported by the Public Health Service South Limburg and the Department of Medical Microbiology, Maastricht University Medical Center +.