HIV risk behaviour of gay men revealed in large US study

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A large multicentre US study has found that over 20% of HIV-negative gay men had receptive unprotected anal sex with a partner they knew to be HIV-positive in the past six months.

The study also found that almost a third of HIV-negative gay men had unprotected receptive anal sex with men of unknown HIV status and that over 37% had insertive anal sex without a condom with HIV-positive men.

These figures come from the baseline data gathered as part of the US EXPLORE study, and are published in the June 1st edition of the American Journal of Public Health.


The EXPLORE study is the first US study designed to test the effectiveness of HIV prevention campaigns by using HIV acquisition as the end-point. Between January 1999 and February 2001 4295 HIV-negative gay men were recruited in six large US cities.



Receptive anal intercourse refers to the act of being penetrated during anal intercourse. The receptive partner is the ‘bottom’.


Insertive anal intercourse refers to the act of penetration during anal intercourse. The insertive partner is the ‘top’. 


The last part of the large intestine just above the anus.


Amyl, butyl or isobutyl nitrite, are recreational drugs sniffed during sex to both intensify the experience and relax anal sphincter muscles.


Refers to the mouth, for example a medicine taken by mouth.

At a baseline visit men were interviewed about their demographic background, and history of sexually transmitted infections (STIs). Using a computer assisted self-completed questionnaire, the men provided details about their sexual behaviour over the past six months. The men then had an HIV test and were screened for bacterial STIs using a urine test and rectal swab.

Only men who are HIV-negative are eligible for admission to the study, and are asked to return at six-monthly intervals when they will again complete the questionnaire about their sexual behaviour and be tested for HIV and bacterial STIs. Men who test HIV-positive will be referred to specialist care.


At baseline, the average age of men entering the study was 34 years, 27.5% were from minority ethnic and racial groups, nearly 36% had a college degree and a little under 60% had an annual household income of over $30,000. Over half the men cited altruistic reasons for joining the study.

Sexual behaviour

Study participants had had an average of seven sexual partners in the past six months, with 42.2% having ten or more. A little under half the men were involved in a relationship with a primary partner, 32.4% knew their partner to be HIV-negative, 6.7% had an HIV-positive primary partner and 9.7% had a partner of unknown status.

The overwhelming majority of men, 78.2% reported having sex with at least one man whose HIV status was unknown to them, and 28.4% said that they had had sex with a man who they knew to be HIV-positive.

When asked about specific sexual behaviour, 45.2% of men said that they had had receptive oral sex with ejaculation, 48% reported unprotected receptive anal sex and 54.9% said that they had had insertive anal sex without a condom.

However, there was evidence that the men in the study were taking steps to reduce their risk of HIV exposure with men tailoring their sexual behaviour to the HIV status of their partner. 46% of men reported that they had had unprotected receptive anal sex with a partner known to be HIV-negative, whilst 20.9% said that they had had receptive anal sex without a condom with a man they knew to HIV-positive. More men reported having unprotected insertive anal sex with both HIV-negative (50.3%) and HIV-positive (37.2%) partners.

Regarding unprotected sex with partners of unknown HIV-status, men again reported more insertive sex (40.7%) than receptive sex (32.2%).

The use of alcohol, cannabis, poppers, hallucinogenic drugs, cocaine and amphetamines in the past six months were all significantly associated with receptive unprotected anal sex with partners who were either HIV-positive or of unknown HIV status.

Approximately 13% of men reported having an STI in the six months before entry into the study, and at baseline 1.8% were found to have a urethral STI and 0.7% tested positive for rectal gonorrhoea.

The investigators comment, “these baseline data underscore that the HIV epidemic among” gay men in the US “continues to be a major public health issue.” Particularly as men with multiple partners who are either HIV-positive or of unknown status are having just as much unprotected sex as men with one primary partner. “Such situations carry risks of disease acquisition from partners who are HIV-positive, a group that includes recently infected men who may report that they are HIV-negative but in fact may be highly infectious.”

In conclusion, the investigators comment, “the EXPLORE baseline data…emphasize the continued need for effective behavioral strategies designed to prevent HIV infection among” gay men.

Further information on this website

Sexual health - factsheets

Fifteen percent of young gay men in South Beach HIV-positive, but no link found with drug use - news story

Rate of unprotected anal sex between men of unknown HIV status increasing in SF> - news story

Multiple psychosocial problems increase gay men's risk of HIV - news story

’False beliefs’ about HIV driving gay men’s risk behaviour - news story

Gay men realistic, not optimistic about HAART - news story

Both older and younger gay men having more unprotected sex in San Francisco - news story

Older gay men with STIs at greatest risk of HIV - news story

San Francisco HIV prevention campaign highlights side-effects - news story

HIV incidence increasing most rapidly amongst older gay men in Amsterdam - news story

High risk pool of gay men with multiple partners growing in the UK - news story

The dark-side of HAART optimism? More unsafe sex and poor adherence - news story


Koblin BA et al. High-risk behaviours among men who have sex with men in 6 US cities: baseline data from the explore study. American Journal of Public Health 93: 926 – 932, 2003.