Study: 1 in 900 unprotected sex acts between HIV-discordant couples results in an infection

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This study analyzed 3,297 couples in Africa in which one partner was HIV positive and the other was not. Over a two-year period these couples periodically had their blood tested and answered questions about their sex lives. During this time there were only 86 new transmissions among the 3,297 couples.

Men were 50% more likely to transmit HIV than women, which may be partially explained by the fact that men generally have higher concentrations of the virus in their blood. Also, women were more likely to have genital herpes, which increased their susceptibility.

When it came to the couples' sex lives, much of the study relied on self-reporting, which is notoriously faulty. Researchers suspect condom use was over-reported; couples claimed condoms were used in 93% of sex acts. If researchers are correct in this assumption, condoms reduce transmission rates by more than 78%. They also found that male circumcision reduced the risk of men catching the virus by 47%.

Another potential problem with the study is that is used couples in which one was living with HIV and the other was not, suggesting that the HIV negative partner might have already had a biological safeguard against the virus. Moreover, this study does not apply to men who have sex with men.


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  • Magic and Cookie Johnson

According to a new study, 1 in 900 unprotected sex acts between couples in which one partner is HIV positive will result in the transmission of the virus to the uninfected partner. The most important factor in determining the risk of transmission is the concentration of the virus in the infected person's blood. Every tenfold increase in concentration results in a threefold increase in the risk of transmission.

These findings reinforce the need for antiretroviral drugs in slowing the spread of HIV. A study out last year found that these drugs, which reduce the concentration of HIV in the blood, can also reduce transmission rates by up to 96%.

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