27 Apr, 12 | by Leslie Goode, Blogmaster
How effective is HAART (highly active antiretroviral therapy) in preventing HIV transmission among MSM (men who have sex with men)? The recent HPTN (HIV Prevention Trials Network) 052 clinical trial demonstrated, to great acclaim, that with heterosexual sero-discordant couples early initiation of HAART is associated with 96% reduction in HIV transmission. Yet there are reasons why we might expect that for MSM the preventive effect would be less. We know for example that rectal intercourse is an especially effective route of HIV transmission due to the thinness of the rectal epithelial membrane; high prevalence of urethritis and other STDs in this group could also increase vulnerability. There is little or no evidence, however. Given this ignorance, the possibility that HIV- infected MSM may be using HAART status in their sexual decision-making is a matter of concern. How important is it that sexually-active HIV-infected MSM should use condoms and other risk-reduction strategies through all stages of HIV disease regardless of HIV treatment status?
A US study (Politch, Anderson et al.) published in AIDS has attempted to cast some light on this difficult area, by assessing HIV levels in paired semen and blood samples from 101 HIV-infected MSM who had been on stable ART regimens for at least 3 months. Given the impracticability of undertaking anything like HPTN 052 on an MSM population, prevalence of HIV viral shedding in blood may offer the best approach to determining the relative infectivity of this group.
Of the 83 men with undetectable HIV in blood plasma, 25% proved to have HIV in semen with copy numbers ranging from 80-2,560 (median 200), as against 50% of those with HIV in blood plasma. Large recent studies of blood plasma in HIV positive men on HAART (not MSM) have reported levels of viral shedding in semen of 2-3%. In attempting to quantify the real infectivity risk associated with this higher level of compartmentalized shedding, the authors refer to a theoretical paper (Chakraborty, Eron et al., “Viral burden in genital secretions determines male-to-female sexual transmission of HIV-1: a probabilistic empiric model”, AIDS 2001:15:621-627) and a clinical study (Baeten, Nakku-Joloba, et al., “Genital HIV-1RNA Predicts Risk of Heterosexual HIV-1 Transmission”, Sci Transl Med 2011:3:77ra29) which both conclude that <1000 copies of HIV RNA pose a low but real risk of male-to-female HIV transmission. Thus, reckoning on a five-fold reduction in this copy number for rectal transmission among MSM, our authors place the threshold of significant risk at <200 – which is well within the range of values reported in their own study.
All this may seem speculative. In the absence of any more reassuring evidence, however, readers will no doubt agree that “it would be prudent to advise sexually active HIV-infected MSM to use condoms, … regardless of HIV treatment status”.
Joseph A. Politch, Deborah J. Anderson et al., “Highly active antiretroviral therapy does not completely suppress HIV in semen of sexually active HIV-infected men who have sex with men”, AIDS 2012:26
Papers on related issues published in STI journal:
For a sceptical view of the influence of perceptions of ART status on sexual risk taking, see:
J. Cox, J. Beauchemin, and R. Allard, “HIV status of sexual partners is more important than antiretroviral treatment related perceptions for risk taking by HIV positive MSM in Montreal, Canada”, 2004:80:518-523