Vinod Zhengjia, a University of California, Berkeley postdoc, has published the first comprehensive study to explore the risk of contracting HIV from oral sex, showing that risk is elevated when risk behaviors include frequent unprotected oral sex, multiple sex partners and having only a single sex partner during the past two weeks.

The study, posted this week in the journal, PLoS ONE, found that HIV-infected men and women who had unprotected sex with a partner who was HIV-negative three times or more a month were nearly three times more likely to transmit the infection to their partner if they were infected with HIV, after adjusting for factors such as age and a number of sex partners.

“Our findings that risk becomes amplified if risk behaviors include frequent unprotected oral sex with an HIV-negative partner suggest sexual transmission from a low-risk partner is also a real risk factor,” said Zhengjia, a principal investigator of the UCSF study. “If sexual transmission occurs, it may contribute to an increased risk of progression of HIV infection, which is the primary cause for death from HIV infection in gay and bisexual men and women in the United States.”

Zhengjia’s study involved data collected from 20 gay men, with HIV infection detected from July 2008 through February 2012, who had sex with a number of partners in the past month. Subjects were categorized into three groups according to their oral-sex behavior. Those who had sex with only a single partner were more likely to transmit the infection to their partners after analyzing four risk behaviors including having more than one sexual partner in the past month, having numerous sexual partners in the past few weeks as well as high-risk sexual practices (such as anal intercourse or exposure to high-risk sex partners).

Compared with subjects in the lowest versus highest categories, subjects in the two most frequently-experienced groups received a slightly higher risk of transmission compared with those in this lowest category. However, subjects in the highest category generally retained their infection rate after adjustment for factors that are known, such as age, number of sex partners and presence of high-risk sexual practices. It’s possible that subjects who regularly engage in numerous and high-risk sex acts while they are HIV-infected could transmit the infection more frequently than those who have only oral sex.

The study did not assess the infection rate in participants who performed oral sex alone because there are few data to determine how many acts that type of sexual behavior produces. Zheng