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Chemsex and diagnoses of syphilis, gonorrhoea and chlamydia among men who have sex with men in the UK: a multivariable prediction model using causal inference methodology
  1. Louis MacGregor1,
  2. Manik Kohli2,
  3. Katharine J Looker1,
  4. Ford Hickson2,
  5. Peter Weatherburn2,
  6. Axel J Schmidt2,
  7. Katy ME Turner1,3
  1. 1Population Health Sciences, University of Bristol, Bristol, UK
  2. 2Sigma Research, Faculty of Public Health & Policy, London School of Hygiene and Tropical Medicine, London, UK
  3. 3Bristol Veterinary School, University of Bristol, Bristol, UK
  1. Correspondence to Dr Louis MacGregor, Population Health Sciences, University of Bristol, Bristol, UK; lm13381{at}


Introduction In the last decade diagnoses of most STIs have risen among men who have sex with men (MSM). Although a significant proportion of this is likely due to increased STI screening, understanding the role of behavioural drivers remains critical. We measure the associations between stimulant use to enhance and prolong sexual experiences (chemsex) and bacterial STI diagnoses in UK MSM, individually considering HIV-diagnosed MSM, pre-exposure prophylaxis (PrEP) users and other MSM.

Methods We used the UK 2017–2018 European MSM Internet Survey data (n=9375). We constructed causal inference models using multivariable logistic regression, calculating adjusted OR (aOR) and 95% CI of the associations between participation in recent (≤12 months) exclusively dyadic or multipartner chemsex versus no chemsex and recent self-reported diagnoses of syphilis, gonorrhoea and chlamydia.

Results Among MSM with an HIV diagnosis, 25% of users indicated recent multipartner chemsex, vs 28% of PrEP users and 5% of other MSM. Adjusting for age, ethnicity, UK birth, cis-trans status, sexual identity, education, settlement size and relationship status, participation in recent multipartner chemsex versus no chemsex was associated with greater odds of recent syphilis, gonorrhoea and chlamydia diagnosis. aORs for recent syphilis, gonorrhoea and chlamydia diagnoses were 2.6 (95% CI 1.7 to 4.1), 3.9 (95% CI 2.6 to 5.8) and 2.9 (95% CI 1.9 to 4.3), respectively, in HIV-diagnosed MSM; 1.9 (95% CI 1.1 to 3.3), 2.9 (95% CI 2.0 to 4.2) and 1.9 (95% CI 1.3 to 2.8), respectively, in PrEP users; and 4.0 (95% CI 2.3 to 6.9), 2.7 (95% CI 1.9 to 3.8) and 2.3 (95% CI 1.6 to 3.4), respectively, in other MSM. Conversely, exclusively dyadic chemsex had no significant associations with bacterial STI diagnoses among HIV-diagnosed MSM, only gonorrhoea (aOR 2.4, 95% CI 1.2 to 4.7) among PrEP users and syphilis (aOR 2.8, 95% CI 1.4 to 5.6) among other MSM.

Discussion Multipartner chemsex may drive the association between chemsex and bacterial STI diagnoses and thus should be the focus of future tailored chemsex interventions. Additionally, PrEP acceptability among MSM and particularly chemsex participants has generated an emergent group suitable for such interventions.

  • syphilis
  • Chlamydia trachomatis
  • gonorrhoea
  • gay men
  • sexual behaviour

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  • LM and MK are joint first authors.

  • Handling editor Laith J Abu-Raddad

  • Twitter @sigmaresearch1, @katymeturner

  • LM and MK contributed equally.

  • Contributors All authors jointly designed this analysis led by LM and MK. LM and MK undertook statistical analyses and model development, with supervision from KMET and FCIH. LM and MK wrote the first draft of the article. LM, MK, KJL, FCIH, PW, AJS and KMET interpreted the results, edited the article and approved the final version. AJS, FCIH and PW led the design and implementation of EMIS-2017 at LSHTM.

  • Funding This analysis was funded by the NIHR Health Protection Research Unit in Evaluation of Interventions at University of Bristol, in partnership with Public Health England (PHE). The views expressed are those of the authors and not necessarily those of the NIHR, the Department of Health and Social Care or PHE. EMIS-2017 was principally funded by the European Union in the framework of the Third EU Health Programme (2014–2020).

  • Competing interests KMET has received funding through the University of Bristol from GlaxoSmithKline for work outside this research.

  • Patient consent for publication Not required.

  • Ethics approval Ethical approval for the original study was granted by the LSHTM Research Ethics Committee

    (review reference 14421/RR/8805) on 31 July 2017.

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

  • Data availability statement Data may be requested from the EMIS-2017 research team.