What is the Risk of Sexual HIV Transmission for HIV-infected Persons With Undetectable Viral Load?

What is the Risk of Sexual HIV Transmission for HIV-infected Persons With Undetectable Viral Load?

ART is considered effective when it consistently suppresses plasma viral load to undetectable levels. However, sexual transmission of HIV from an infected partner who was on ART with a repeatedly undetectable plasma viral load has been documented [8]. An infected partner's genital (seminal or vaginal) fluid viral load may play a greater role than plasma viral load when evaluating the risk of sexual transmission of HIV. The likelihood of HIV transmission in the setting of ART is influenced by a number of factors, several of which are described below.

The Meaning of “Undetectable” Viral Load: Persistence of Virus in Plasma and Seminal Fluid

Periodic blood plasma viral load monitoring is used to measure ART effectiveness. The goal of effective ART is the long-term suppression of plasma viral load, usually defined as the maintenance of a level of HIV virus that is below the threshold detectable by available tests. While plasma viral load tests are reliable, they have limitations: virus levels below a minimum concentration may not be detected. Studies have shown that persistent virus is found in peripheral blood mononuclear cells [9, 10] even when individuals have sustained undetectable plasma viral load levels.

Genital fluid viral loads are not routinely measured in persons on ART. Although ART reduces concentration of virus in seminal fluid [11], virus persists within cells present in seminal fluid of some men who are on ART with undetectable plasma viral load [12-13]. ART also is associated with decrease in cervicovaginal fluid viral load; however, ‘breakthrough' shedding has been observed in some studies [14-17]. Therefore, the potential for transmission exists despite sustaining undetectable viral load while on effective ART.