Recent studies show that HIV treatment that is effective in suppressing the disease works well at preventing the spread of the disease between heterosexual partners. These Canadian findings were the result of a trial funded by NIAID.

The idea of lessening HIV transmission with treatment is not entirely new. In fact, one study from 2011 revealed that the risk of spreading HIV to a partner is reduced by 96 percent when treatment starts early and is taken consistently. The study focused specifically on heterosexual couples in which only one partner was HIV positive.

More than 1,700 heterosexual couples across four continents signed up to be a part of the clinical trial. As a part of the study, all of the couples received training on how to avoid transmission of HIV. Infected individuals were assigned at random to either begin immediate antiretroviral treatment or to delay starting treatment until immunocompromised. Approximately 600 couples did not complete the entire trial, but the data from the other 1,100+ was sufficient to get results. What was learned?

The healthy partner was 93 percent less likely to contract HIV if the infected partner began treatment immediately. In the case of couples where the treatment was begun early on, only eight partners ended up being infected. In fact, four of those individuals were diagnosed early on, showing that the longer treatment went on, the less likely the health partner was to be infected.

It is also important to note that in all four individuals who were infected later on, the partner receiving treatment had not had the disease fully suppressed for one reason or another. In the case of those for whom the treatment worked, there was no transmission after the early part of the study. Another important discovery was that, for those who waited to start treatment, it took longer to suppress the virus, thus leaving a longer window where transmission risk was higher.

The moral of the story: to protect your partner, start treatment early and stick with it to ensure suppression.