Among young
Thai men who have sex with men, 6 in 100 acquire HIV each year. With the
average age at infection being 26, this explosive epidemic is affecting a far
younger group of men than the gay epidemics in Western countries. These are the
headline findings of the first three years of a study to monitor HIV incidence,
reported by Frits van Griensven to the Eighteenth International AIDS Conference
in Vienna on
Tuesday.
More
encouragingly, a second study from Thailand, reported the same day,
suggested that HIV prevalence could be declining in men who have sex with men,
after having peaked at about 30% in 2007.
Thailand is often seen as a lesson in early
and effective HIV control. However, until recently, efforts have largely
concentrated on commercial sex workers, their clients and injecting drug users.
The ongoing spread of HIV among men who have sex with men (MSM) was largely
ignored until a much overdue study of Bangkok MSM in 2005 found an HIV
prevalence of 17%.
In the
incidence study, a cohort of 1292 Bangkok MSM was recruited, which is being
followed at four-monthly intervals. Recruitment began in April 2006 and was
completed by January 2008. Participants are all Thai nationals, male at birth,
resident in the Bangkok area, aged 18 or over, and have had anal or oral sex
with a man in the six months before recruitment. Participants were recruited
from the sexual health clinic where follow-up visits were conducted, through a
website, from a range of bars, saunas and parks used by MSM, and through
community organisations.
Men
recruited were relatively young (73% aged 29 and under), and were frequently
born outside of Bangkok
(64%). A majority were employed, well educated and identified as homosexual or
gay.
In this
sample, 22% of men were HIV-positive at baseline but were generally unaware of
their infection. After three years of study, another 135 men had acquired HIV.
In a 12-month period, the annual rate of HIV acquisition (incidence) was 5.9
per 100 person years. This did not vary
between years 1, 2 or 3 of the study.
The mean
age at seroconversion was 26.4, and the median was 26. “This means that 50% of
the men who became infected during follow-up were younger than 26 years, and we
have seen quite a large number of cases where men got infected when they were 18 or
19 years of age,” van Griensven commented. He noted that in cohort studies in
other parts of the world, men are typically in their thirties when they
seroconvert.
Among those
men who were initially HIV-negative, it was the youngest men who were actually
most likely to have acquired HIV by the end of the study. Using the
Kaplan-Meier method to estimate the chances of remaining HIV-negative after four
years, 89% of those aged 30 or over would be negative, in contrast to 71% of
those aged 18 to 21 at recruitment.
This
suggests that men are most vulnerable to infection when they are younger
– men
who did not acquire HIV at a young age are less likely to acquire it when they
are older. van Griensven said that behavioural surveys showed that on average
younger men had more drug use, unprotected sex and sexual partners.
The age
difference is also illustrated by the odds ratios for having either prevalent
or incident HIV infection. Prevalence relates to an infection acquired at any
time in the past, so older men were more likely to have prevalent HIV. A man
aged 30 or over was three times more likely to have prevalent HIV than a man
aged 18 to 21 (odds ratio 3.2)..
On the
other hand, incidence refers only to newly acquired infections. A man aged
18 to 21 was also almost three times more likely to have incident HIV than a man
aged over 30 (odds ratio 2.7).
As well as
age, other factors associated with incident (new) infections in the multivariate analysis
were using drugs for sexual pleasure (primarily crystal meth, odds ratio 2.9);
using taking the receptive position (odds ratio 1.9); inconsistent condom use
(odds ratio 5.3 but with wide 95% confidence intervals, 1.3 to 21.8); past
herpes infection (odds ratio 1.6) and past syphilis infection (odds ratio 2.5).
A second study from Thailand...suggested that HIV prevalence could be declining in men who have sex
with men,
after having peaked at about 30% in 2007
In response
to a question, van Griensven stated that his study could not indicate whether
incidence is rising or falling in Bangkok.
However, a separate study of HIV prevalence among Bangkok men who have sex with men may suggest
that prevalence is in fact falling.
Nonetheless,
the survey method (a series of cross-sectional surveys, conducted at two-year
intervals) is not the most reliable way of measuring these changes. Slightly
different recruitment methods used for each survey could result in a different
profile of men being recruited to different surveys, with the result that
apparent changes in HIV prevalence may not be genuine.
The surveys
have been conducted over an eight-year period, in 2003, 2005, 2007 and 2009.
Men aged 15 and over, who report anal or oral sex with another man in the past
six months, are recruited at entertainment venues, saunas and parks.
Overall HIV
prevalence rates were 17% in 2003; 28% in 2005; 31% in 2007; and 25% in 2009.
The increase from 2003 to 2005 was statistically significant, whereas the
apparent decrease from 2007 to 2009 was not (p=0.22).
For those
under the age of 22, HIV prevalence was 13% in 2003; 22% in 2005; 22% in 2007; and
13% in 2009.
Regarding
risk behaviours, almost all 2003 survey respondents reported that they had
engaged in anal sex at some point in their life, but only about two-thirds of respondents
did so in 2009 (98 vs 62%; p<0.001).
On the
other hand, almost no men in 2003 reported using drugs in the three months
preceding the survey, but in 2009, one in five had done so (4 vs 20%; p<
0.001). Drug use during last sex also increased, from 0.7 to 4.2% (p<
0.001).
Consistent
condom use in the past three months remained steady at around 64%
– 68% across
survey rounds.