Men who have sex with men may now be at considerably higher risk of acquiring HIV than other at-risk groups such as female sex workers or young people of either sex, if findings by the International AIDS Vaccine Initiative (IAVI) of HIV incidence at two centres in Kenya can be generalised to other populations.
The study, which compared the Kenyan populations with a largely heterosexual group from South Africa, also found lower-than-expected HIV incidence amongst female sex workers and their clients. The researchers also found that recruiting MSM into the study was easier than expected, but note that there was a particularly high dropout rate in MSM.
They comment that while MSM “need urgent risk reduction interventions, and may be a suitable cohort for future HIV prevention studies,” because African MSM face considerably legal and social hurdles in coming forward, “careful consideration of the counselling and clinical needs, follow-up schedule and social support is vital to ensure continuing research participation.”
The aim of the study was to collect data on HIV and STI incidence and risk factors in three populations in Kilifi, a district north of Mombasa, and the Kangemi district of Nairobi, both in Kenya, and from Gugulethu township in Cape Town in South Africa, the better to target HIV vaccine trials.
The researchers recruited 716 people in Mombasa, 653 in Nairobi and 465 in Cape Town, The researchers primarily used participants to recruit their peers in South Africa, where background HIV prevalence at 28% is ten times higher than in Kenya, but in Kenya recruited attendees at HIV testing centres, via outreach work in bars and brothels, and via ‘snowball’ sampling (asking members of a particular group to recruit others from the same group). The original idea had been to collect data on high-risk heterosexuals including sex workers but, as the researchers comment, “it quickly became apparent that MSM were willing to come forward and participate in HIV prevention research”.
Somewhat different monitoring and follow-up criteria were used in the three centres. In Cape Town participants were monitored monthly and followed up for one year while in the two Kenyan cohorts participants were monitored quarterly for two to four years. In Mombasa participants were examined for STIs at every visit but in Nairobi and Cape Town only examined if they had symptoms. As a result annual STI incidence was much higher in Mombasa (23%) than in the other two centres (3.7% and 4.4%).
The average ago of participants was mid-20s (slightly older in Nairobi); nearly 70% were women in Cape Town, 50% in Nairobi and 36% in Mombasa. Participants in Capt Town were almost entirely heterosexual men and women and were not sex workers.
In Mombasa 56% of men (36% of the study population) was an MSM; 63% of men said they had sold sex (mainly to other men) and 54% had bought it. Three-quarters of female participants said they were female sex workers while one in 20 women said they had bought sex.
In Nairobi nearly all women defined as a sex worker and 85% of the men had bought sex; 22.5% of the men had had sex with other men and 33% defined as a male sex worker.
There was a high dropout rate in the study: 13% did not return after their enrolment visit, 37% altogether left the study prematurely. Annual attrition rates were 22% in Cape Town, 20% in Mombasa and 10% in Nairobi.