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Original article
Incidence and risk factors associated with chlamydia in men who have sex with men: a cohort analysis of Victorian Primary Care Network for Sentinel Surveillance data
  1. Anna Wilkinson1,2,
  2. Carol El-Hayek1,
  3. Christopher K Fairley2,3,
  4. David Leslie4,
  5. Norm Roth5,
  6. B K Tee6,
  7. Margaret E Hellard1,
  8. Mark Stoové1
  1. 1Centre for Population Health, Burnet Institute, Melbourne, Australia
  2. 2School of Population Health, University of Melbourne, Melbourne, Australia
  3. 3Melbourne Sexual Health Centre, Melbourne, Australia
  4. 4Victorian Infectious Diseases Reference Laboratory, Melbourne, Australia
  5. 5Prahran Market Clinic, Melbourne, Australia
  6. 6The Centre Clinic, Melbourne, Australia
  1. Correspondence to Anna Wilkinson, Burnet Institute, 85 Commercial Road, Melbourne, Victoria 3004, Australia; awilkinson{at}


Background Chlamydia is the most commonly notified sexually transmitted infection (STI) in Australia. Incidence studies of chlamydia in men who have sex with men (MSM) are rare and offer important public health information.

Objective To determine chlamydia incidence in MSM presenting at high caseload clinics and describe predictors of infection.

Methods The Victorian Primary Care Network for Sentinel Surveillance of bloodborne viruses and STIs (VPCNSS) links testing, demographic and behavioural data from individual testers at participating clinics. Data from MSM with more than one chlamydia test at the VPCNSS site between April 2006 and June 2010 were included. Chlamydia incidence per 100 person-years (PY) was calculated and Cox regression used to examine predictors of incidence.

Results 1206 positive tests for chlamydia were detected among 6333 MSM across 11 409 PY of follow-up. Overall chlamydia incidence was 10.6/100 PY (95% CI 10.0 to 11.2) and was highest among MSM aged 16–29 years (12.9/100 PY, 95% CI 11.7 to 14.1), presenting with STI symptoms (16.0/100 PY, 95% CI 14.2 to 18.0), HIV positive (18.5/100 PY, 95% CI 16.6 to 20.6) and self-identified sex workers (14.3/100 PY, 95% CI 10.0 to 20.6). Significant predictors of chlamydia infection among MSM were younger age (adjusted hazard ratio (aHR)=1.9, 95% CI 1.5 to 2.3), self-identifying as a sex worker (aHR=1.6, 95% CI 1.0 to 2.6), being HIV positive (aHR=2.6, 95% CI 1.8 to 3.8), presenting with STI symptoms (aHR=1.7, 95% CI 1.4 to 2.1) and reporting >10 sex partners in the past 6 months (aHR=2.5 95% CI 1.4 to 4.6).

Conclusion These results show that MSM represent a key risk population for chlamydia in Australia and identify a number of high-risk MSM subpopulations for whom clinical and public health interventions are warranted.

  • Chlamydia
  • incidence
  • men who have sex with men
  • risk factors
  • sexually transmitted infections
  • sexual health
  • epidemiology (general)
  • public health
  • chlamydia
  • anogenital cancer
  • AIDS
  • bacterial vaginosis
  • epidemiology (clinical)
  • syphilis
  • chancroid
  • chlamydia infection
  • genital ulcers
  • genitourinary medicine

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  • Funding Victorian Government Department of Health; NHMRC provide funding to MEH.

  • Competing interests None.

  • Ethics approval Department of Health Human Research Ethics Committee; Department of Justice, Human Research Ethics Committee; Family Planning Victoria, Human Research Ethics Committee; The Royal Children's Hospital, Melbourne, Human Research Ethics Committee; The Royal Women's Hospital, Human Research Ethics Committee; The Alfred, Ethics Committee.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement All authors, external and internal had full access to all of the data in this study and take responsibility for the integrity of that data and the accuracy of the data analysis.