Opposites Attract Study

The challenge: 

In 2011, research in heterosexual serodiscordant couples (that is, where one partner in the couple is HIV-positive and the other partner is HIV-negative) showed that early antiretroviral treatment of the HIV-positive partner was associated with a 96% reduction in the risk of transmitting HIV to their HIV-negative partner. However, there is much less evidence for gay male couples. Opposites Attract is one of only two studies ever to be conducted that explores this research question in gay men.

The project: 

Opposites Attract was an observational cohort study of gay male serodiscordant couples. The key research question of the study was: To what extent do HIV treatments in the HIV-positive partner reduce the risk of HIV transmission to the HIV-negative partner in these couples?

The method: 

Opposites Attract enrolled gay male serodiscordant couples in three Australian cities (Sydney, Melbourne, Brisbane), and in Rio de Janeiro, Brazil, and Bangkok, Thailand. The couples were followed-up over time, visiting their study clinic at least two times per year. At each visit, the HIV-positive partner had his viral load tested, and the HIV-negative partner was tested for HIV antibodies. Both partners were also tested for sexually transmissible infections, and they both completed a questionnaire. 

The study began recruiting in early 2012 in Australia, and in May 2014 in Brazil and Thailand. In total, the study enrolled 358 couples, with 343 of these attending at least one follow-up visit. Follow-up of couples ended on 31 December 2016.

The results: 

Over 588 couple-years of follow-up (“couple-years of follow-up” means the cumulative total amount of time that all the couples were in the study), the couples reported a total of 16,800 acts of anal sex without condoms, and 12,447 acts of anal sex without condoms when the HIV-positive partner had undetectable viral load and the HIV-negative partner was not taking PrEP. There were no “linked” HIV transmissions in these couples. A “linked” transmission is where genetic analysis of the virus shows that the HIV came from the HIV-positive partner in the couple to his HIV-negative partner. So, no HIV-negative man in the study contracted HIV from his HIV-positive study partner.

The impact: 

This is an exciting result and provides further evidence that the risk of HIV transmission when someone's viral load is undetectable is effectively zero. The final results of the Opposites Attract Study were reported at the International AID Society Conference on HIV Science in Paris, France, in July 2017, and then published in The Lancet HIV, in July 2018. Since the results were reported, the evidence from Opposites Attract has been referenced in HIV policies and strategies, by bodies such as the United States Centers for Disease Control and Prevention, the World Health Organization, UNAIDS, and the Australasian Society for HIV, Viral Hepatitis and Sexual Health Medicine. Most importantly, these results have confirmed the message that “Undetectable = Untransmittable” and will help to overcome the stigma and discrimination faced by people living with HIV.

Project contact: 

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