A group of scientists, including several from the University of Washington School of Public Health, has found that certain types of vaginal bacterial are associated with an increased risk of HIV infection among women.

Scott McClelland, a professor of epidemiology and global health at the UW School of Public Health, is lead author of the new study, which investigates absolute concentrations of bacteria for more defined HIV risk analysis. Findings were published Jan. 25 in The Lancet Infectious Diseases.

Prior to this paper, it was posited that bacterial vaginosis, or the condition when there is too much of a particular bacteria in the vagina, might contribute to HIV transmission and the disproportionate burden of HIV infection in African women. Because of new advances in molecular biology, researchers’ understanding and categorizations of vaginal bacteria types have catalyzed new studies on the association between specific vaginal bacteria and HIV acquisition.

Although previous research in this area has found strong associations, the new research investigates absolute concentrations of bacteria for more defined risk analysis.

“It’s important to measure absolute concentrations of bacteria for a couple of reasons,” said McClelland, who is also a professor of medicine at the University of Washington. “First, there can be important differences between relative abundance, which is measured by broad range [polymerase chain reaction] and deep sequencing, and absolute concentration, which is measured using quantitative PCR assays. Second, relative abundance comparisons are more likely to overlook potentially important differences in species that have low relative abundances.”

According to McClelland, absolute concentrations of bacteria provide a more targeted approach to identify specific vaginal bacteria. For a decade, the team of researchers analyzed data from five cohorts of eastern and southern African women, including female sex workers, pregnant and postpartum women, and women in mixed-status relationships. The data identified the specific vaginal bacteria communities that were common among those who acquired HIV.

“These results suggest that high concentrations of certain bacteria may increase women’s susceptibility to HIV,” McClelland said. “This opens up the possibility of testing prevention interventions targeted towards reducing or eradicating these vaginal bacteria in women at risk for HIV infection.”

Higher diversity vaginal bacteria communities are more common in women of African and Hispanic descent than women of Asian or European origin. This helps inform population-level differences in HIV transmission and prevalence. Additionally, because bacterial vaginosis is extremely heterogeneous (with multiple potential causes), defining individual vaginal bacteria that are associated with HIV risk can provide specific targets and future strategies for HIV prevention research. 

Study co-authors include Jairam Lingappa, Sujatha Srinivasan, John Kinuthia, Grace John-Stewart, Walter Jaoko, Barbra Richardson, Krista Yuhas, Tina Fiedler, Kishorchandra Mandaliya, Matthew Munch, Nelly Mugo, Craig Cohen, Jared Baeten, Connie Celum, Julie Overbaugh and David Fredricks.