Undetectable viral loads in blood is not a guarantee that HIV is also undetectable in semen, according to a new study involving 101 HIV-positive men who have sex with men (MSM) conducted in Boston and published online ahead of print by the journal AIDS. Of the 83 men with undetectable virus in blood samples, roughly a quarter of them—21 MSM in total—had semen with detectable HIV. 

Though the study conducted by Joseph Politch, PhD, of Boston University School of Medicine and his colleagues didn’t look at whether those with low-but-detectable levels of HIV in their semen were necessarily more likely to transmit the virus than those with undetectable seminal viral loads, the authors nevertheless caution that a risk of ongoing HIV transmission potentially remains in the absence of barrier protection during sexual activity. “Until more information on transmission risk in MSM is available,” they write, “it would be prudent to advise sexually active HIV-infected MSM to use condoms and other risk-reduction strategies throughout all stages of HIV disease regardless of HIV treatment status.” READ MORE