June 10, 2009
If your past several viral load test results have been undetectable, there's about a 95 percent chance that your next one will be, too, according to a large Swiss study published in the May 6 issue of HIV Medicine, the official journal of the British HIV Association. The new findings may reignite the debate over just how likely people with HIV are to transmit the virus if their HIV viral load has been consistently undetectable while they were on treatment.
That debate exploded in January 2008, when the Swiss Federal Commission for HIV/AIDS released a controversial report for Swiss physicians. The report examined a series of studies involving heterosexual couples in which one partner was HIV positive and the other was HIV negative (called "magnetic" or "serodiscordant" couples). The report stated that it was almost impossible for a heterosexual, HIV-positive person on HIV meds to pass HIV to his or her partner during unprotected sex, provided the HIV-positive person:
Most of those finer points were lost when the story went public, however. Headlines screamed that the commission was giving HIV-positive people a nearly unequivocal green light to have unprotected sex. (The venerable Agence France-Presse may have taken the oversimplification cake with "Patients on AIDS Drugs Don't Transmit Virus.") Accusations flew, the researchers came under fire, clarifications were issued, and ultimately the furor died down.
But the question remains: Are there cases in which HIV-positive people can have unprotected sex with their HIV-negative partner without having to worry about the possibility of transmitting HIV?
Central to answering this question is the issue of exactly what it means to have an "undetectable" viral load. Any number of things can happen during the three-month span that usually passes between a person's viral load tests, such as an interaction with a new herbal supplement, prescription medication or over-the-counter drug. And sometimes, albeit rarely, a person's viral load can briefly spike for reasons that are still unknown.
But what are the chances that any of these things will happen? If a person had an HIV viral load test two months ago and it found her or his viral load was undetectable, what are the odds that's still the case now?
This study was conducted by some of the very researchers who were at the center of the Swiss Federal Commission brouhaha. In fact, three of the researchers -- Pietro Vernazza, M.D., Bernard Hirschel, M.D., and Enos Bernasconi, M.D., all prominent Swiss HIV experts -- had been co-authors of the very report that ignited the controversy in January 2008. The study's primary author was Christophe Combescure, Ph.D., of the Division of Clinical Epidemiology at University Hospital Geneva.
The thrust of the study was an examination of viral load test results in 6,168 people participating in the Swiss HIV Cohort Study. All were HIV-positive people who had at least one viral load test result below 50 copies/mL (the lowest level at which commonly used viral load tests are able to detect HIV) between May 2003 and December 2007 while they were taking HIV treatment. Some other quick facts about the participants:
Unsurprisingly, the researchers found that the more undetectable viral loads a person already had, the more likely it was that her or his next viral load would also be undetectable. But there was a limit. A person with one undetectable viral load had an 84.5 percent chance of his or her next viral load being undetectable. The odds rose steadily to 94.5 percent for people with five undetectable viral loads -- and then remained at around 95 percent for people with more than five undetectable viral loads.
When they looked at the reasons why people developed a detectable viral load, the researchers found (unsurprisingly) that having missed more than one dose of HIV meds in the past four weeks was a major factor. They also found that a detectable viral load was more likely to occur among people who were on HIV meds but who were not taking combination HIV treatment, also known as HAART.
Interestingly, the Swiss study also noted that the specific clinic that an HIV-positive person went to impacted her or his odds of maintaining an undetectable viral load. The researchers suggested this might be because centers use different procedures to conduct and analyze viral load tests, possibly causing variation in the test results.
Do these results help or hurt the argument that it can sometimes be "safe" for some HIV-positive people to have unprotected sex with their HIV-negative partners? Despite their deep involvement in the controversial Swiss statement of January 2008, the researchers avoid making any definitive claims in this study. The closest they come is this somewhat ominous line within the study's conclusion: "Our data leave open the possibility that unexplained high [viral loads] in seemingly well-controlled patients, although rare, can occur."
Are those odds low enough to warrant having sex without protection? The researchers avoided giving an opinion on the issue. But we hope that won't stop you from offering your take.