Studies: homosexual transmission

Attia and colleagues did not include in their recent meta-analysis a prospective study examining the effect of antiretroviral treatment on HIV transmission in gay men first presented in February 2009 to the Sixteenth Conference on Retroviruses and Opportunistic Infections in Montreal,1 with further information presented in April 2009 to the Fifteenth Annual British HIV Association Conference in Liverpool.2 This study, involving 1144 gay men attending an HIV treatment centre in Brighton between 2000 and 2006, is the first to examine the risk of transmission in a cohort of gay men, and other men who have sex with men (MSM).

The investigators used clinical and epidemiological information to identify the factors involved in new HIV infections in gay men and, by performing phylogenetic analysis on the HIV from 859 individuals, 41 'likely transmitters' were identified, 29 (70%) of whom had never taken HIV treatment and nine of whom had interrupted their treatment at the time of transmission. As expected, the study found an association between a higher viral load and a greater risk of HIV transmission, with each log10 increment in viral load increasing the risk of HIV transmission by 68%.

Taking HIV treatment was associated with a 96% reduction in the risk of HIV transmission; of the three transmissions on treatment seen during 3556 person-years of follow-up, one is thought to have originated in an individual with an undetectable viral load. No further details are available.

This is not the first recorded case of HIV transmission during sex between men where the infected partner has an undetectable viral load, however. In a case report from Germany, published in August 2008, and confirmed by phylogenetic analysis, a gay man who had maintained an undetectable viral load on treatment since 2000 apparently infected his partner between 2002 and 2004 after reporting unprotected anal intercourse on a number of occasions. Neither partner reported a sexually transmitted infection and both reported that their relationship was monogamous.3

References

  1. Fisher M et al. HIV transmission amongst men who have sex with men: association with antiretroviral therapy, infection stage, viraemia and STDs in a longitudinal phylogenetic study. Sixteenth Conference on Retroviruses and Opportunistic Infections, Montreal, 2009
  2. Fisher M et al. HIV transmission amongst men who have sex with men: association with infection stage, viraemia and STIs in a longitudinal phylogenetic study. HIV Medicine 10 (Supp 1), 018, 2009
  3. Sturmer M et al. Is transmission of HIV-1 in non-viraemic serodiscordant couples possible? Antiviral Therapy 13:729-732, 2008