Understanding the Risk of Sex With a Partner With HIV

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Yesterday Charlie Sheen announced in an interview that he had been diagnosed with HIV four years ago. Since his diagnosis he has been getting treatment and according to Charlie and his doctor he has an undetectable viral load. That means that using standard technology available today, particles of the HIV virus cannot be detected in his blood. This is the goal of treating HIV and our ability to suppress the virus means that people can have an almost normal life and life expectancy.

For many, the most surprising revelation was that since his diagnosis he has had sex without a condom with two women who knew his status. On today’s episode of our show, one of those women, nurse Amanda Bruce, came on to talk about why she felt comfortable engaging in this behavior, which gave us an excellent opportunity to talk about how far we’ve come with HIV treatment. But the question you are all probably asking is how likely is it for a woman without HIV to contract it from having sex with an HIV-positive man with an undetectable viral load? Well, that is a great question but a little tricky to answer.

Studies have suggested that the risk of transmission of HIV in couples in which the HIV-positive partner has an undetectable viral load is extremely low, but many of the couples in these studies have had a high rate of condom use. Our best estimate of the risk of condomless sex comes from the PARTNER Study. This is a large study following couples in which one partner is HIV positive with an undetectable viral load and one partner does not have HIV at all. In 2014 the authors presented some preliminary results of the study that showed that not a single person who had condomless sex with their enrolled partner (an estimated 44,439 sex acts) had contracted HIV from them. That doesn’t mean the risk is zero, however; but it is likely to be very close to zero. We can’t yet say it’s zero, because when events are rare you need an extremely large sample size to say that they never occur.

Based on the results of the PARTNER Study the risk of transmitting the virus is extremely low – somewhere between zero or almost zero and the maximum estimate of about 1 in 3,000 per episode, when an HIV-positive man has unprotected sex with an HIV-negative woman. Another way of looking at it is the risk is somewhere between the chance of winning the grand prize in the Powerball Lottery (1 in 292,201,338) and what is considered the lifetime risk of getting struck by lightning (1 in 3,000). We will need to see more data over a longer period of time to shrink the range of this estimate down.

Charlie Sheen and his girlfriend, however, reduced the risk even more, because his girlfriend took pre-exposure prophylaxis drugs (PrEP). These are a combination of anti-HIV drugs that people take on a daily basis to prevent HIV infection. Studies have show that PrEP can reduce the risk of HIV infection by more than 90 percent. Some doctors are against this belt-and-suspenders approach to prevention, because the risk of transmission is already so low in a person with an undetectable viral load that even such a huge additional percentage decrease in risk doesn’t decrease their actual risk of infection by much more. It does, however, increase their risk of side effects from the drugs. On the other hand, some doctors and many patients may find comfort in further reducing the risk and feel empowered that they have more control over their destiny by taking the medications themselves, rather than relying on their partner to continue to take their own medications and have an undetectable viral load. Either way, the safest thing is still to always use a condom; this decreases not only the risk of HIV transmission, but also the risk of other sexually transmitted diseases.