The Real Risks of Sex With Someone Who Has HIV

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Charlie Sheen on the Today show. Photo: Peter Kramer/NBC

On the Today show Tuesday morning to talk about being HIV-positive, Charlie Sheen said that it's "impossible" that he transmitted the virus to any of his sexual partners. Sheen has an undetectable viral load, meaning that he's being treated and the virus cannot be found in his blood. He says he told all of his partners about his diagnosis before sex, and that he's had unprotected sex with two people since being diagnosed. Leaving aside whether it's ever a good idea to sleep with Charlie Sheen in the first place, is it true that HIV can't be transmitted when the virus is undetectable?

Sheen's doctor, Robert Huizenga, M.D., an associate professor of clinical medicine at the University of California, Los Angeles, appeared alongside the actor to explain that Sheen was immediately put on a treatment of anti-viral drugs following his diagnosis. Dr. Huizenga said transmission of the virus is incredibly rare among people who have undetectable viral loads and use protection responsibly. "We can’t say that that’s zero, but it’s a very, very low number."

How low? As Melissa Dahl explains on Science of Us, a recent study spent six years following more than 1,100 couples where one partner was HIV-positive. It found that early anti-viral treatment reduced the risk of transmission by 93 percent. Another study, currently in its second year, has thus far found zero cases of transmission between partners, and some of the couples weren't using condoms.

But "undetectable viral load" refers to the level of virus in a person's blood only. The virus might still be found in genital fluids like semen, pre-ejaculate, and vaginal fluids. That's why experts recommend that people with HIV use condoms when having any kind of sex: vaginal, anal, or oral. (Yes, oral sex is included.)

Regardless, some couples in HIV-affected relationships don't use condoms, in part because of the advent of a preventive pill called Truvada, more commonly known as pre-exposure prophylaxis, or PrEP. In a study published just yesterday in the journal JAMA Internal Medicine, researchers at an STD clinic provided PrEP to 437 men and transgender women who have sex with men, a population that has the highest risk of new HIV infections. After one year, only two of them contracted HIV — and they were both people whose blood levels of the drug were low, suggesting they only took about half of the doses.

It's also possible that people are less concerned about unprotected sex with HIV-positive partners than they used to be. After all, human immunodeficiency virus (HIV) is no longer the death sentence it was considered in the '80s or '90s. Even Sheen's doctor said he's more worried about his patient's substance abuse than he is about the virus: "My biggest concern with Charlie as a patient is substance abuse and depression from the disease, more than what the HIV could do in terms of shortening his life because it's not going to." Still, there's no vaccine or cure for HIV or AIDS, the final stage of the infection, so it pays to be careful.