Increase in serodiscordant casual sex among Sydney gay men at a time when HIV diagnoses have not increased

Roger Pebody
Published: 28 January 2009

Between 2003 and 2006, there was an increase in the numbers of HIV-negative gay men in Sydney who reported having unprotected anal intercourse with casual HIV-positive partners, report researchers in the online edition of AIDS and Behavior. However the researchers do not believe that these men form "a core group of high risk men".

Iryna Zablotska and her colleagues from the University of New South Wales analysed data from two cohort studies among Sydney gay and bisexual men: the Positive Health cohort of 760 HIV-positive men, and the Health in Men cohort of 1427 HIV-negative men. Both studies asked identical questions about sexual behaviour in annual surveys from 2003 to 2006, including questions on sex with partners of a different HIV status (rather than, as in some other studies, sex which could have been with a partner of a different HIV status).

Among the HIV-negative men, whilst the number having sex with casual partners decreased from survey to survey, there were small but statistically significant increases in the numbers having serodiscordant sex. Those having sex with casual partners they believed to be HIV positive rose from 11% to 13%, and the number specifically having unprotected anal intercourse with those men increased from 3% to 4%.

The number of HIV-positive men reporting serodiscordant casual partners did rise, but there was no statistically significant rise in unprotected anal intercourse with them.

The study examined a number of behaviours that have been previously found to be associated with sexual risk-taking, and confirmed that serodiscordant unprotected anal intercourse with casual partners was more common among men with higher numbers of sexual partners, men who met partners online or in sex clubs, Viagra users, those who injected drugs, men who used 'party' drugs regularly and those having ‘esoteric’ sexual practices (fisting, sex toys, water sports, bondage etc).

However the researchers note that men who had risky sex did not do so consistently. Over 85% of the men who reported having serodiscordant unprotected anal intercourse only reported it at one of their annual interviews, and they typically reported that behaviour with just one or two partners in the previous six months.

The researchers therefore argue that very few men consistently look for unprotected sex with casual partners or show a total disregard for risk. However, "there may be a context, event or setting that men move in and out of, or participate in periodically," they write. Further investigation of these contexts and situations is required to better understand men’s behaviour.

They also note that while serosorting (sex with partners of the same HIV status) is increasing among Sydney gay men, their study demonstrates that disclosure of HIV status does not prevent every instance of serodiscordant unprotected sex. In interpreting this, they suggest that it is possible that unprotected anal sex with serodiscordant partners is simply replacing unprotected sex with partners of unknown HIV status. Another possibility they offer is that disclosure might commonly take place when there is a degree of intimacy between partners, which also makes it difficult to insist on condom use.

Moreover they comment that the apparent increase in risk-taking has occured at a time when HIV diagnoses have not increased in Sydney. They suggest that it is plausible that other risk reduction strategies such as the negative man being the insertive partner or the positive partner practising early withdrawal may have had an impact.


Zablotska IB et al. Increases in unprotected anal intercourse with serodiscordant casual partners among HIV negative gay men in Sydney. AIDS and Behavior (published online ahead of print), 2008.

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