Undetectable Viral Load Essentially Eliminates HIV Transmission Risk in Straight Couples

A recent review indicated that heterosexual serodiscordant couples have a low risk of HIV transmission if the HIV-infected partner has an undetectable viral load as a result of successful antiretroviral (ARV) therapy. The study by the National AIDS Treatment Advocacy Policy was presented at the Third International Workshop on HIV and Women in Toronto, Canada.

Researchers combined data from six studies of serodiscordant heterosexual couples. Three studies provided data on HIV transmission rates, ARV history, and viral load of the HIV-infected partner. These studies included 991 couples with 2,064 person-years of follow-up. The researchers found a 0.0 per 100 person-years transmission rate. The other three studies included rates of transmission and treatment history of 5,233 couples. When these three studies were combined with the previous three, the researchers found a pooled transmission risk of 0.14 per 100 person-years. This means that if 1,000 serodiscordant couples in which the HIV-infected partner is on ARV therapy with an undetectable viral load had sex for one year, approximately one or two non-infected partners would become infected with HIV.

In the six studies, the four transmissions took place before the HIV-infected partner had been on ARVs for six months; therefore, the seropositive partner may not have reached an undetectable viral load by that point. The researchers performed another analysis excluding the data from these transmissions. The result of this second analysis was a transmission risk of 0.0 per 100 person-years.

Sten H. Vermund, M.D., Ph.D., director of the Institute for Global Health at Tennessee's Vanderbilt University, warned that individuals who have what appears to be an undetectable viral load may have what he calls, "viral spikes," which may intermittently put a partner at risk of HIV infection. He advised that to have a zero risk of transmitting the virus to others, individuals should "be on antiretrovirals religiously and also use condoms."

The conference abstract is available at www.natap.org/2013/HIVwomen/HIVwomen_01.htm.