A new study co-authored by UC Berkeley researchers has found that the rate of HIV transmission due to infidelity is higher than previously thought.
The study, published Feb. 5 in the medical journal The Lancet, determined that HIV is usually passed from men to women. Additionally, researchers found that men are most likely to be infected from infidelity while women are more likely to be infected before entering a stable partnership. This discrepancy may be due to the fact that younger women tend to be involved with older men, who have likely had more sexual partners and therefore more exposure to sexually transmitted infections.
The study was conducted by postdoctoral researcher Steve Bellan, then a doctoral student in environmental science policy and management, and professor Wayne Getz in the campus College of Natural Resources. The study examined the differences between transmission among single people compared to that of cohabiting partners. They hope their findings can be used to better target and treat HIV.
“If you ask people if they are having sex outside their partnership, there are various reasons to not give an honest answer as you can imagine,” Getz said. “(Those surveyed) underreport quite dramatically the rate they have extra-couple kinships.”
“We looked at the proportion who were infected within the partnership, we looked at the background rate in populations and we looked at how long couples had been in a relationship,” Getz said. “Then we used a mathematical model to estimate if they were infected outside of the relationship.”
The study found that out-of-couple sex accounted for 27 to 61 percent of all HIV transmissions in men and 21 to 51 percent in women.
“21 and 50 percent may seem broad to some,” Getz said. “The likely value is somewhere in (the middle of) that range, but as scientists we have to be conservative.”
Due to the study’s findings, the researchers say they believe that HIV prevention should be targeted at just the overall sexually active population and not only those in serodiscordant couples — that is, those in which one partner is infected and the other is not.
“Some researchers have called that anyone with HIV go on treatment immediately to protect their partner even if they’re not sick yet,” Bellan said. “Our results show that’s necessary because there’s a lot of transmission going on,”
Jonathan Dushoff, a biology professor at McMaster University and co-author of the study, said that some studies in the past have overestimated within-couple infection.
“The main contribution of the report is to carefully quantify the proportion of transmission that comes through different routes,” he said in an email. “We found that pre-, within- and extra- were all important.”