HIV transmission in serodiscordant couples


one issue that comes up a lot is the transmissability of HIV in serodiscordant couples when the HIV-positive person has a suppressed viral load. a letter-to-the-editor was just published, reviewing 6 relevant studies (see HIV transmission suppressed VL JAIDS 2014 in dropbox, or doi.org/10.1097/QAI.0000000000000471).  lacking the best data, the researchers assumed that a surrogate for suppressed viral load was if the  HIV-positive partner had been on combined antiretroviral treatment (cART) for >6 months (since usually the viral load is suppressed by then). they found:

--at most one transmission in 113,480 sex acts, of which 17% were not condom-protected.
--for that one transmission, data were not adequate to see if it happened before or after than 6-month mark
--so, their estimation varies as follows:
    --case 1: no transmission after 6 months -- upper bound of risk-per-sex act was 8.7 per 100,000
    --case 2: 1 transmission after 6 months -- upper bound of risk-per-sex act was 13 per 100,000

--then, they added the results of the PARTNER study presented at the CROI (conference on retroviruses and opportunistic infections) meeting in Boston in 2014 (see http://www.hivandhepatitis.com/hiv-prevention/hiv-test-treat/4553-croi-2014-no-one-with-undetectable-viral-load-transmits-hiv-in-partner-study​ ), which looked at 767 HIV-discordant couples (40% gay) where there was condom-less sex and the HIV-infected partner had a viral load <200 copies/mL on most recent testing, with the 2-year interim analysis showing:
    --NO transmissions so far!!! (the study will go on to 2017 -- this is only an abstract of an interim report from the meeting)
--so, by adding this data to the above 6 studies, the estimates for case 1 above decreased to 5.2/100,000 sex acts and from case 2 to 7.9/100,000 sex acts

so, this is helpful. however, there needs to be more data on gay couples, since most of the above is on heterosexual couples. I do have some concern about reported discordance between suppressed viral load in blood and in semen. The studies i've seen are mostly in MSM (men who have sex with men), so i do have concern about the relative lack of data in the above studies about MSM. one recent article from  Boston found that of 83 men with undetectable HIV in blood, 25% had HIV in their semen with HIV levels of 80 to 2560 copies/mL, with multivariate analysis showing sexually-transmitted infections/urethritis and unprotected insertive anal sex with an HIV-infected partner to be independent predictors of seminal fluid HIV detection (see hiv semen viral load discordance AIDS 2012 in dropbox, or AIDS 2012, 26:1535–1543​)​. other studies have found detectable semen HIV levels in MSM with non-detectable plasma HIV levels in those with herpesvirus infections (eg CMV or EBV). but the study above is pretty reassuring, suggesting that transmission is still pretty rare (though likely non-zero). so, i think patients should still be warned that there is still a possibility of getting HIV infection if they don't use condoms, as well as the variety of other potential sexually-transmitted infections.

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