With modern antiretroviral medications, nearly every HIV-positive man and woman can be successfully treated today. This doesn’t mean that the infection has been eliminated from the body—there will always be stored copies of the virus hidden away—but we can essentially stop any new virus from being produced. This is what we call having an “undetectable viral load.”
It means that there is so little virus in the blood that even our most sensitive tests can’t find any. We’ve known for a while now that once the viral load is undetectable, a weakened immune system can recover to near-normal levels. We’ve also seen evidence that successful control of viral replication with antiretroviral medication can decrease the risk of transmitting HIV from person to person. Quality evidence was limited to heterosexual couples, though—until now.
The PARTNER study was designed to look specifically at the risk of transmission of HIV in men who have sex with men when one partner is HIV-positive and on treatment. This large European trial—begun in 2010 and completed last year—recruited serodiscordant couples (one HIV positive and one negative) who were already having condom-free sex. The HIV-positive partner must have been treated with an undetectable viral load in order to participate, and safer-sex counselling was given to both partners. Every six months, the participants completed a sexual-history questionnaire.
On average, there were 43 condom-free sex acts per year for each couple. And here’s the interesting news: there have been zero cases of HIV transmission so far. That’s zero transmissions after an estimated 16,400 condom-free sex acts between men who have sex with men in this study. These striking results support a strategy recently pioneered in British Columbia called “treatment as prevention” or TAsP. This strategy aims to eliminate new HIV infections by treating everyone living with HIV at the time of diagnosis, rather than waiting until a person is at risk of becoming sick.
So can we use these data to recommend condom-free sex for all serodiscordant couples? Not quite. This study won’t be complete until 2017, so we will have to wait and see if this trend persists over the next couple of years. As with any research study, the longer we observe this group, the more confidence we can have that the results are truly accurate.
For now, even with zero transmissions, we still need more data and time. There is a potential that viral loads could transiently increase if medication doses are missed or if someone takes a course of an interacting medication or herbal remedy. This could place the HIV-negative partner at short-term risk. Condom-free sex also introduces the risk of infection with other sexually transmitted infections, such as hepatitis C or syphilis.
While we aren’t ready to recommend sex without condoms for all, the PARTNER study certainly provides confidence that the risk of transmission from someone with an undetectable load on treatment is exceptionally low. This can at least help to minimize some of the fear that many HIV-positive men have of passing on the virus to their partner. Time will tell if widespread treatment as prevention will put an end to unacceptably high rates of HIV infection in Canada.
Dr. Malcolm Hedgcock is a Toronto-trained family doctor living and working in Vancouver. He has a special interest in gay men’s health issues, including the primary care of those living with HIV and AIDS.