At the Sixteenth Conference on Retroviruses and Opportunistic Infections in Montreal on Monday morning, two back-to-back oral presentations affirmed that HIV is indeed often detectable in semen despite undetectable viral loads in blood plasma. The two studies found measurable HIV RNA ("viral shedding") in 3% to 14% of seminal fluid samples taken from study participants with undetectable plasma viral loads.
Since the 'Swiss statement' of January 2008, which described HIV-positive individuals on effective antiretroviral therapy and without sexually transmitted infections (STIs) as "sexually non-infectious", the issue of how antiretroviral treatment affects sexual infectiousness has been hotly debated. In particular, case reports have indicated that HIV may indeed be present in the semen of men who are on successful antiretroviral therapy, with undetectable blood plasma viral loads.
The Toronto study
Prameet Sheth reported findings from a Toronto-based Canadian study which looked at two groups of HIV-positive men: a prospective cohort of 25 men just beginning antiretroviral treatment (ART), and a second group who had been on effective ART for at least four years with fully suppressed viral load. In the first group, viral RNA was measured in blood plasma and in semen at baseline (before beginning ART), and then every two to four weeks up to 24 weeks. A Bayer Diagnostics branched DNA (b-DNA) assay was used, with a lower limit of detection of 50 copies/ml for blood and 300 copies/ml for semen.
Viral load in blood plasma became persistently undetectable (5000 copies/ml) in 4 of the 25 (16%); the highest level measured in semen was 16,026 copies/ml.
Most pertinently, HIV RNA was detectable in 19/116 (14%) of the samples taken after blood plasma viral load became undetectable. Cell-free virus isolated from the semen of the "highest shedder" was found to be infectious in an in vitro test. (No other patients' samples were analysed.)
Patterns of viral shedding varied: one man had persistent, sustained seminal HIV without ever reaching undetectability, but most had single "blips" among otherwise undetectable measurements. Nine of the twelve detectable measurements (75%) occurred after seminal viral load had initially become undetectable.
Prolonged, successful treatment did not eliminate instances of seminal HIV shedding: the study also took single samples from 13 men in whom HIV had been suppressed on ART for over four years (median, 82 months), finding detectable virus in the seminal fluid of 4 of the 13 (31%).
Viral shedding was more likely in men with higher baseline seminal viral loads. "Shedders" had median baseline values of 4.21 log10, versus 3.46 log10 in "non-shedders" (p = 0.03). Neither baseline blood plasma viral load, CD4 cell count, nor herpes serostatus were found to have an effect. Nor was any difference found between those on PI-based versus NNRTI-based regimens, nor due to varying drug concentrations in seminal fluid.
Several questions arose concerning the specific assays used in this study. For one, b-DNA is more sensitive than PCR viral load assays, possibly explaining why this study found somewhat higher values than other studies of HIV in semen have found (including the Paris study described next).
The Paris study
Anne-Geneviève Marcelin reported comparable findings from her team, who followed HIV-positive men in the assisted reproduction programme at the Pitié-Salpêtrière Hospital in Paris. Since 2002, this programme has provided sperm washing services to HIV-positive male/HIV-negative female couples.
This study examined 264 paired samples of blood and semen taken from 145 HIV-positive men between 2002 and 2008. HIV RNA was measured with the Taqman HIV-1 assay, with a limit of detection of 40 copies/ml in blood and 200 copies/ml in semen. Seminal HIV RNA was measured in the seminal fluid remaining after spermatozoa were removed by centrifuge.
HIV was undetectable in both blood plasma and semen in most of the sample pairs (225/265, or 85.3%), and was detectable in both in nine (3.4%) of the sample pairs. In 23 samples (8.7%), HIV RNA was undetectable in semen but detectable in plasma.
Of most interest, however, HIV RNA was undetectable in blood plasma but detectable in semen in seven samples. As each of these was from one of seven different patients, this represented 2.7% (7/265) of the total samples, but 4.8% (7/145) of the men in the study. The HIV RNA levels in these seminal fluid samples ranged from 255 to 1230 copies/ml.
As in the Toronto study, most of the seminal shedding occurred as "blips" – six of the seven men had shown concordant, undetectable blood and seminal HIV RNA on at least one other occasion. The men were on a variety of antiretroviral regimens, and the antiretroviral drugs present in the blood were consistently detectable in semen as well.
These two studies both identified repeated instances of detectable virus in semen despite undetectable levels in blood plasma, although the frequency of occurrence varied. Both presenters related their findings directly back to the controversial "Swiss statement". In particular, Dr Marcelin noted that in all such participants, blood plasma viral load had been undetectable for at least six months, and no other STIs were identified in the course of clinic screening, the criteria specified for "uninfectiousness" in that statement.
Questions remain as to how HIV RNA levels in semen actually correspond to transmission risk. In particular, the threshold level of seminal viral RNA that corresponds to a significant transmission risk is not known. The Parisian study did not, in fact, see any cases of transmission from these men to their HIV-negative partners, except in one non-adherent patient who had had plasma viral rebound.
While acknowledging the remaining uncertainties, both presenters concluded that an undetectable plasma viral load due to successful ART does not reliably eradicate HIV in semen, and does not eliminate the risk of HIV transmission during unprotected intercourse.
Sheth P et al. Persistent HIV RNA shedding in semen despite effective ART. Sixteenth Conference on Retroviruses and Opportunistic Infections, Montreal. Abstract 50, 2009.
Marcelin A-G et al. Detection of HIV-1 RNA in seminal plasma samples from treated patients with undetectable HIV-1 RNA in blood plasma. Sixteenth Conference on Retroviruses and Opportunistic Infections, Montreal. Abstract 51, 2009.