In a country
where sex between men and women is the main transmission route for HIV, the
biggest increase in a woman’s risk of getting HIV happens when she gets
married. That’s one reason why sexual abstinence campaigns don’t work: most women
with HIV were abstinent - till their
But in countries
where most transmission is between gay men there has been an underlying
assumption that it’s all fuelled by casual sex. This idea was recently challenged
by a US
study1, which calculated that two-thirds of gay men who acquire HIV do
so from their regular partner.
The study didn’t
look at actual HIV transmission episodes in a group of men. Instead, it
analysed data from the National HIV Behavioral Surveillance System (NHBS), a
study of 3652 HIV-negative and positive gay men in five US cities between 2003
and 2005.2 This looked at the number of sexual partners men had in a
year, both main and casual; the perceived HIV status of their partners; the
proportion having anal sex who didn’t use a condom last time they had sex; and whether
they were insertive (‘top’) or receptive (‘bottom’). The NHBS study also took
anonymous saliva samples for HIV screening from half of the men they studied.
It could therefore tell whether gay men’s knowledge of their HIV status was
Because the NHBS
only collected data about the last sexual episode, one missing thing needed to
know was how many times men had actually had sex during the year with main and
casual partners. They therefore added in data from a previous study, the
Vaccine Preparedness Study, which recruited 3617 gay men in six US cities
between 1995 and 1997.
Encouraging couples to test, or re-test, for HIV the moment they get involved with someone emotionally has several benefits.
With all these
data, the researchers were able to work out what proportion of HIV infections
must have come from regular partners, and the answer was around two-thirds –
68%. Even when they tested their model to destruction by putting in the minimum
possible estimated rate of unsafe sex with main partners and the maximum
possible for casual partners, still more than half of HIV infections came from
several reasons for this. Firstly, men had more actual occasions of sex with
their main partner. In raw numbers there were about 195,000 occasions of sex
between main partners and about 173,000 episodes of casual sex. So gay men
don’t exactly behave like Indian brides, but they still have more sex (about 80
times a year on average) with their regular partner than with casual partners.
were more likely to have anal sex with main, rather than casual partners and
were more likely to be the receptive partner too. Forty per cent had been anally
receptive last time they had sex with their boyfriend (though they might have
been active too) but only a quarter of them the last time they had casual sex.
were considerably less likely to use condoms with main than casual partners. Men
used condoms for anal sex (in either role) 72% of the time with casual partners
but only 43% of the time with main partners. Add all these together and you get
a lot more instances of unsafe sex with main partners per year than with casual
was around 25% in both casual and main partners. Men were pretty bad at either
knowing or guessing their own or their partners’ HIV status. When the
researchers looked at actual HIV transmissions, they worked out that only 16%
of men who caught HIV had known their partner had HIV.
In contrast 46%
of men who acquired HIV caught it from someone they had believed to be HIV-negative,
and 55% of transmissions from main partners came from men who believed
themselves to be negative. In casual sex, 63% of transmissions happened in
situations where the partner’s status had been unknown.
diagnosed HIV infection were therefore the group least likely to be responsible for HIV transmission. This was because,
when one partner was known to have HIV, couples were no less likely to use
condoms with their main partner than during casual sex.
There were a
couple of other standout findings from the study. Firstly, although being the
receptive partner (the ‘bottom’) accounted for nearly 70% of infections, 28% of
infections were acquired by the insertive partner (the ‘top’). This is more
than predicted from previous studies, though some HIV campaigners did comment
that some men might have lied about being a ‘bottom’ as it is still
stigmatised. Note also that the study found that 2 to 3% of infections came
from oral sex – a figure that backs up earlier studies.
annual HIV incidence – the proportion of this group that acquires HIV every year
– was calculated to be 2.2%. Given that this is ten times the observed
mortality rate among gay men in the Vaccine Preparedness Study,3 the
number of gay men in the USA with HIV will continue to grow, at least until
significant numbers start dying of old age, unless HIV incidence is cut
obviously has huge implications for HIV prevention messages. It’s well known
that people use condoms much less with their main partner and for many couples this
is because condoms are seen as a sign of distrust. Trying to get regular
partners who don’t use condoms already to use them can be a challenge.
couples to test, or re-test, for HIV the moment they get involved with someone
emotionally has several benefits. If one partner does test positive for HIV it
not only means they are in a much better position to look after their own
health, but successful treatment will also reduce their infectiousness. And
regardless of test results, testing for HIV is a powerful prevention tool,
bringing people into contact with sexual health services, but most importantly,
opening up a discussion between partners about sexual health and safer sex.
prevention message is most appropriate, however, depends on one question not asked
by the survey. In the words of Roger Tatoud, Senior Programme Manager for the International
HIV Clinical Trials Research Office at Imperial
College in London, “If most people get HIV from their
main partner, where did he get it from?” This is also a dilemma faced by
researchers into heterosexual transmission. There are two theories:
monogamy’ theory is based on the idea that committed relationships among gay
men and especially young gay men might not last very long, and this is borne
out by the finding that the men averaged 1.4 ‘main partners’ a year. If the
average interval between HIV tests or, for those who’ve never tested, between
first sex and the most recent, is longer than or near the average length of
committed relationships, then there are going to be a lot of men entering new
relationships who don't know they have HIV. Message: test as soon as you get
theory, on the other hand, assumes there is far more sex going on outside a lot
of main relationships than the researchers captured, both because respondents
didn’t tell them about it (we know people lie about sex to even the most
confidential survey) or because the researchers made assumptions about what ‘main
relationships’ mean to gay men, for instance that emotional commitment means
monogamy, and so didn’t ask clearly enough about it. Message: have an agreement
to maintain safer sex outside your main relationship.
is right, this study challenges assumptions that offering gay men marriage and
the chance to settle down with the dog and Radio 4 might mean less HIV
transmission, and will cause some rethinking in the world of HIV prevention.