High HIV incidence among young Thai men who have sex with men

The first ever study of the incidence of new HIV infections among men who have sex with men in Thailand has shown that each year 5% acquire HIV, reported Wipas Wimonsate from the Thai Ministry of Public Health at the International AIDS Conference in Mexico City on August 4^th. The men recruited to this study will continue to be followed for three years, and the data from the study will help the planning of HIV prevention in this group.

Thailand is often seen as a lesson in early and effective HIV control. However, efforts have largely concentrated on commercial sex workers and their clients as well as injecting drug users. The ongoing spread of HIV among men who have sex with men (MSM) had been largely ignored until a much overdue study of Bangkok MSM in 2005 found an HIV prevalence of 17%.

Although there has been an increase in HIV prevention activities in the past few years, when the prevalence study was repeated in 2005 and 2007, the figure had jumped to 28% and then to 31%. Given that prevalence was high in men under the age of 22 (who had been sexually active for a brief period), this suggested that incidence must be very high. Moreover four-in-five of those infected with HIV in 2005 were unaware of their infection.

In the current study, a cohort of 1,292 Bangkok MSM was recruited, who will be followed at four monthly intervals over a three year period. 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 web site, 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, 23% of men were HIV-positive at baseline. Although 48% of the cohort had previously tested for HIV, none of those with HIV had been previously aware of their infection.

In July 2008, follow-up data were available covering 985 person years of participation in the cohort study. A total of 54 men had sero-converted to HIV, which corresponds to an annual HIV incidence of 5.5%.

The mean age for those acquiring HIV was 24 (range 18-42).

Risk factors for HIV infection

Further information was provided on those who had HIV at baseline. Wipas Wimonsate described the risk factors for HIV infection as being similar to those found in other settings. In multivariate analysis, they included being aged 30 or over (compared to men 21 and under, odds ratio (OR) 2.32). Men without university/tertiary education were more likely to have HIV (OR 1.72), but on the other hand, infection was more likely in those who were employed (OR 1.70).

Unsurprisingly, men who usually had receptive anal sex were more likely to have HIV (OR 1.71), as were men with HSV-2 (OR 3.89) and rectal gonorrhoea (OR 2.54). Moreover, men who had used the recreational drug poppers in the past four months were more likely to be positive (OR 2.29).

Men who had never tested for HIV before were more likely to have HIV (OR 1.60). However men who frequently worried about getting HIV in the future were also more likely to have their fears confirmed (OR 1.96).

There was also information on sexually transmitted infections at baseline. Prevalence was high: 44% of men had hepatitis B, 20% had genital herpes (HSV-2), 4% had syphilis, 9% had chlamydia, and 6% had gonorrhoea.