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Quantifying heterogeneity in sexual behaviour and distribution of STIs before and after pre-exposure prophylaxis among men who have sex with men
  1. Daphne Amanda van Wees1,2,
  2. Sophie Diexer1,
  3. Ganna Rozhnova1,3,
  4. Amy Matser2,
  5. Chantal den Daas4,
  6. Janneke Heijne5,
  7. Mirjam Kretzschmar1
  1. 1Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands
  2. 2Department of Infectious Diseases, Public Health Service of Amsterdam, Amsterdam, The Netherlands
  3. 3BioISI – Biosystems & Integrative Sciences Institute, Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal
  4. 4Aberdeen Health Psychology Group, University of Aberdeen Institute of Applied Health Sciences, Aberdeen, UK
  5. 5Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, The Netherlands
  1. Correspondence to Dr Daphne Amanda van Wees, Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands; daphne.van.wees{at}rivm.nl

Abstract

Objectives: Pre-exposure prophylaxis (PrEP) use may influence sexual behaviour and transmission of STIs among men who have sex with men (MSM). We aimed to quantify the distribution of STI diagnoses among MSM in the Netherlands based on their sexual behaviour before and after the introduction of PrEP.

Methods: HIV-negative MSM participating in a prospective cohort study (Amsterdam Cohort Studies) completed questionnaires about sexual behaviour and were tested for STI/HIV during biannual visits (2009–2019). We developed a sexual behaviour risk score predictive of STI diagnosis and used it to calculate Gini coefficients for gonorrhoea, chlamydia and syphilis diagnoses in the period before (2009 to mid-2015) and after PrEP (mid-2015 to 2019). Gini coefficients close to zero indicate that STI diagnoses are homogeneously distributed over the population, and close to one indicate that STI diagnoses are concentrated in individuals with a higher risk score.

Results: The sexual behaviour risk score (n=630, n visits=10 677) ranged between 0.00 (low risk) and 3.61 (high risk), and the mean risk score increased from 0.70 (SD=0.66) before to 0.93 (SD=0.80) after PrEP. Positivity rates for chlamydia (4%) and syphilis (1%) remained relatively stable, but the positivity rate for gonorrhoea increased from 4% before to 6% after PrEP. Gini coefficients increased from 0.37 (95% CI 0.30 to 0.43) to 0.43 (95% CI 0.36 to 0.49) for chlamydia, and from 0.37 (95% CI 0.19 to 0.52) to 0.50 (95% CI 0.32 to 0.66) for syphilis comparing before to after PrEP. The Gini coefficient for gonorrhoea remained stable at 0.46 (95% CI 0.40 to 0.52) before and after PrEP.

Conclusions: MSM engaged in more high-risk sexual behaviour and gonorrhoea diagnoses increased after PrEP was introduced. Chlamydia and syphilis diagnoses have become more concentrated in a high-risk subgroup. Monitoring the impact of increasing PrEP coverage on sexual behaviour and STI incidence is important. Improved STI prevention is needed, especially for high-risk MSM.

  • sexual behaviour
  • pre-exposure prophylaxis
  • chlamydia infections
  • gonorrhoea
  • syphilis

Data availability statement

All data relevant to the study are included in the article or uploaded as supplemental information. Not applicable.

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Data availability statement

All data relevant to the study are included in the article or uploaded as supplemental information. Not applicable.

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Footnotes

  • Handling editor Jane S Hocking

  • Contributors All authors contributed to the study concept. DAvW and SD analysed and interpreted the data. GR, AM, CdD, JH and MK supervised the overall study and provided substantial contributions to the interpretation of the data. DAvW wrote the first draft of the manuscript, and acted as guarantor for the work. All authors contributed to subsequent drafts and approved the final version of the article for submission.

  • Funding This project was funded by the Netherlands Organisation for Health Research and Development ZonMw grant 522 008 010.

  • Competing interests None declared.

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

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