The rate of new HIV infections among gay men in Amsterdam
has increased steadily since the introduction of effective antiretroviral
therapy, investigators report in the online edition of AIDS.
Receptive unprotected anal sex, a larger number of partners
and recent infection with gonorrhoea were all associated with an increased risk
of infection with HIV. Most of the infections were acquired from casual
partners, but the researchers also found evidence of transmissions within
Trends in new HIV infections have been monitored over 25 years in the Amsterdam cohort,
and the investigators comment, “to our knowledge, this is the first study in
recent years to document the HIV-1 incidence rate and risk factors for HIV
transmission among MSM [men who have sex with men] in an observational cohort.”
They believe that their results provide “evidence for
ongoing substantial HIV transmission among MSM” and that increased levels of
testing alone cannot explain why HIV prevalence has risen substantially among
gay men in recent years.
In industrialised countries like the Netherlands gay men
remain a focus of the HIV epidemic. Several countries have reported increased
numbers of new HIV diagnoses among gay men, and studies have also shown that
more gay men are reporting unprotected anal sex – the sexual activity most
associated with HIV transmission.
Investigators from the Amsterdam Cohort Study wished to gain
a clear understanding of HIV incidence and risk behaviour among gay men. They
therefore analysed 25 years of data gathered between 1984 and 2009.
A total of 1642 gay men who were HIV-negative at the time of
recruitment to the cohort were included in their analysis. Every three-to-six
months the men were tested for HIV and completed questionnaires about their
recent sexual behaviour and history of sexually transmitted infections.
Median age at the time of recruitment was 29 years, 81% of
the men were Dutch and 55% had a college degree. Individuals were followed for
a median of 6.2 years.
There were 217 incident HIV infections, and the median age
at seroconversion was 34 years.
HIV incidence was 8.6 per 100 person years in 1985, but then
fell sharply and was 1.3 per 100 person years in 1992. Incidence then remained
relatively stable and was 1.4 per 100 person years in 1996, the year effective
HIV therapy was introduced. Thereafter a modest but steady increase in
incidence was seen, reaching 2.0 per 100 person years in 2009.
However, the investigators note that the increased incidence
in recent years was not significant.
Accompanying these incidence trends were changes in HIV risk
Over three-quarters of men reported recent unprotected anal
sex in 1984, but this had fallen to 33% in 1988, but this had increased to 38%
by the end of 1995, and by the end 2009 the proportion of men reporting
unprotected anal sex in the previous six months was 55%. This increase was
significant (p < 0.01).
Risk factors for infection with HIV were not having a degree
(risk ratio [RR] = 2.00; 95% confidence interval [CI], 1.24-3.21), having five
or more recent sex partner (RR = 2.54; 95% CI, 1.58-4.08), receptive
unprotected anal sex (RR = 4.06; 95% CI, 2.37-6.96), and a recent history of
gonorrhoea (RR = 5.84; 95% CI, 2.49-13.71).
In three-quarters of cases, the source of the incident
infection was a casual partner.
But steady partners were an increasingly important source of
new infections, especially for older men.
“It could be that…older men are more likely to have a
partner who is also older and therefore has a higher probability of being HIV-infected,”
suggest the investigators. They also propose that older men and those in longer
relationships “often break negotiated safety rules…due to changes in sexual
preferences, relationship context, and for other reasons.”
increases in sexual risk behaviour from 1996 onwards, HIV continues to spread
among MSM,” conclude the investigators, “receptive unprotected anal intercourse
with casual partners remains the strongest risk factor for acquiring HIV
The investigators recommend that men with casual partners
should be a prevention priority. However, they also stress “our findings also
suggest the need to pay specific attention to prevention measures regarding
sexual behaviour with steady partners.”