Gay and bisexual men who reported engaging in chemsex (the use of specific drugs to enhance or facilitate sex) were five times more likely to be newly diagnosed with HIV, nine times more likely to be diagnosed with hepatitis C and four times more likely to be diagnosed with a sexually transmitted infection (STI) during a 13-month follow-up period, according to London data published this week in HIV Medicine.

“This is the first published study to demonstrate a significant association between chemsex disclosure and new HIV diagnosis,” said Dr Mark Pakianathan and colleagues at St George’s University Hospital, London. Clinicians and public health officials should use the findings to identify a population particularly vulnerable to HIV acquisition who could be targeted for pre-exposure prophylaxis (PrEP) and other prevention interventions, they say.

During routine appointments for sexual health care at St George’s between June 2014 and July 2015, 1840 gay and bisexual men were asked questions about mental health, substance use and chemsex. (A previous aidsmap.com article reported on harms associated with chemsex.) Their ages ranged from 14 to 82 years, but the median was 34. Just under a third were born outside the UK and the cohort was ethnically diverse.

Glossary chemsex The use of recreational drugs such as mephedrone, GHB/GBL and crystal meth before or during sex. multivariate analysis An extension of multivariable analysis that is used to model two or more outcomes at the same time. adjusted odds ratio (AOR) Comparing one group with another, expresses differences in the odds of something happening. An odds ratio above 1 means something is more likely to happen in the group of interest; an odds ratio below 1 means it is less likely to happen. Similar to ‘relative risk’. odds ratio (OR) Comparing one group with another, expresses differences in the odds of something happening. An odds ratio above 1 means something is more likely to happen in the group of interest; an odds ratio below 1 means it is less likely to happen. Similar to ‘relative risk’. disclosure In HIV, refers to the act of telling another person that you have HIV. Many people find this term stigmatising as it suggests information which is normally kept secret. The terms ‘telling’ or ‘sharing’ are more neutral.

Currently engaging in chemsex was reported by 286 men (16.5% of all men).

Drugs most commonly used for chemsex were mephedrone (198 men), GHB/GBL (152 men), crystal methamphetamine (126 men), cocaine (54 men), other amphetamines (36 men) and ketamine (22 men). Of note, the St George’s researchers used a wider definition of chemsex than some other groups, who define it as only the use of the first three drugs in a sexual context.

Men often used more than one drug at the same time. Injecting drug use was reported by 74 men.

Whereas 1.8% of men who did not report chemsex had a new HIV diagnosis during 2014 or 2015, this was the case for 8.6% of men who were involved in chemsex. In multivariate analysis (which took into account a range of other factors which influence HIV infection), chemsex was associated with a fivefold increase in the risk of HIV infection (adjusted odds ratio 5.1, 95% confidence interval 2.6-10.1).

The researchers comment that chemsex sessions may last several days and involve mucosally traumatic sex with multiple partners. Given the high incidence of HIV in this population, sexual partners who met at chemsex parties may be men who have very recently acquired HIV, have not been diagnosed and have an extremely high viral load.

A new diagnosis of hepatitis C occurred in 0.2% of men who did not report chemsex and 2.8% of men who did (eleven men in total). In multivariate analysis, this amounts to a ninefold increase in risk (adjusted odds ratio 9.2, 95% confidence interval 2.3-36.3).

Similarly, diagnoses of STIs were elevated in men involved in chemsex. This was true for all STIs (adjusted odds ratio 3.5), rectal STIs (4.5) and acute bacterial STIs (3.9).

Gay and bisexual men attending sexual health services should be assessed for chemsex participation, the researchers say. “Disclosure should prompt health promotion, harm minimization and wellbeing interventions.”