January 6, 2014
Longitudinal Studies Shed Light on MSM Per-Contact HIV Risk
A new analysis of the risk of HIV transmission posed by specific sexual acts found that younger men who have sex with men and MSM of color have a higher risk of the contracting the virus. Publishing their findings in the Journal of Acquired Immune Deficiency Syndromes (JAIDS), researchers pooled data from three longitudinal studies of MSM from the era preceding modern antiretrovirals (ARVs) and the early-ARV era. Covering overlapping time periods that spanned 1998 to 2003, the studies, which all required the men to be HIV negative upon entry and which gathered reports on their sexual behavior, included the HIV Network for Prevention Trials Vaccine Preparedness Study, the EXPLORE behavioral efficacy trial, and the VAX004 vaccine efficacy trial.
The investigators concluded that unprotected receptive anal intercourse (URAI) with an HIV-positive partner was the most risky act, with an estimated 0.73 percent chance of seroconversion for each act. The per-contact risk (PCR) for URAI with a partner of unknown HIV status was 0.49 percent. For protected receptive anal intercourse (PRAI) and unprotected insertive anal intercourse (UIAI) with an HIV-positive partner, the PCR was a respetive 0.08 percent and 0.22 percent. PRAI with a partner of unknown status had a PCR of 0.11 percent.
The scientists speculate that the similarity they saw in the PCRs between the pre-modern ARV and early-modern ARV eras was a consequence of relatively low proportions of MSM with a suppressed viral load during both eras. Today, just 30 percent of HIV-positive MSM have an undetectable viral load and therefore a 96 percent reduced risk of passing on the virus. A vast increase in the current use of ARVs among MSM with the virus would most certainly drive down PCRs among HIV-negative MSM.
The PCRs were elevated among young MSM. The researchers speculated one reason may be that younger men lack the skills of their older counterparts when it comes to negotiating safer sex, or to using risk reduction strategies such as withdrawing before ejaculation.
There was also evidence that Latino MSM had a higher PCR for UIAI with HIV-positive men. And there was inconclusive evidence that black MSM had higher PCRs than white MSM for URAI and UIAI with HIV-positive men. If these data reflect reality, one reason for the disparities may be that MSM of color report that they are more likely to have sex with a man of their same race or ethnicity. Untreated sexually transmitted infections may also contribute to the disproportionate rates of HIV among minority MSM.
Search: Men who have sex with men, MSM, gay, per-contact risk, HIV, transmission, Journal of Acquired Immune Deficiency Syndromes, JAIDS, EXPLORE, HIV Network for Prevention Trials Vaccine Preparedness Study, VAX004.
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comments 1 - 5 (of 5 total)
joe khumalo, westonaria, 2014-02-02 21:47:27
more information needed
POZ Editors, New York, NY, 2014-01-10 11:54:26
Still Confused, all the decimals you see refer to the percent risk of acquiring HIV from one incident of a specific sexual act. If there is a 0.08 percent per-contact risk (PCR) for one act of protected receptive anal intercourse (PRAI) with an HIV-positive partner, you can express that as a decimal by saying the chance of HIV transmission is 1 in 0.0008. You can express that as a probability by dividing 1 by 0.0008 = 1,250. Therefore, according to that estimate, HIV-negative men who have sex with men have a chance of 1 in 1,250 of acquiring HIV by having URAI with an HIV-positive partner.
Still Confused, , 2014-01-09 12:01:42
Sorry - I'm not a math major. Your risks are posted as decimals - does that mean that 1.00 is 100%? Does this mean that .73 or whatever is almost 75% chance of contracting HIV? Please clarify for us artsies, thanks!
POZ Editors, New York, NY, 2014-01-08 15:51:13
MatthewJ, thanks for your inquiry. Indeed, the data do estimate a higher risk during PRAI with a partner of unknown status compared with an HIV-positive one. Keep in mind that these are the findings of one particular set of data; other studies may or may not come to similar conclusions. More importantly, in the fine print of this study, the investigators give a more broad range of estimates of what the actual risk of each given act may be; the estimate ranges of the risks between the two sexual acts you mentioned overlap almost entirely. PRAI with an HIV-postive partner has a 0.08 PCR, but a 0.0-0.19 percent estimated range; PRAI with unknown has a PCR of 0.11, but an estimated range of 0.02-0.2 percent. So it's not safe to conclude that PRAI with a partner of unknown status is more risky on average than PRAI with someone who is HIV positive. In essence, they are both relatively low-risk behaviors, especially compared with URAI with an HIV-positive partner or with one of an unknown status. And it is because these insertive, protected sexual acts are so much lower risk than the other acts that it is likely difficult to come up with enough data to show more precisely how risky they are.
MatthewJ, Arcadia, CA, 2014-01-08 12:40:08
comments 1 - 5 (of 5 total)
Ok, I'm confused. URAI with a poz guy is .73 percent and goes down to .49 percent with unknown status. But PRAI is .08 with a poz guy and then goes UP to .11 when it's with unknown? How does that work?
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