“All kinds of things—lubricants, semen, bacteria, feces—get put into the vagina,” says Forney. “But most women are healthy most of the time.” He and other microbiologists would like to discover the keys to that resilience, which probably relies on interactions between the vaginal wall cells, the microbes living there, and the woman’s immune system.
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In 2006, reproductive epidemiologist Jenifer Allsworth set out to determine just how many women in the U.S. were affected by BV. Crunching data from a national health survey and 3,727 vaginal swabs analyzed by Hillier’s group, Allsworth showed that 29 percent of all U.S. women aged 14 to 49 were positive for BV. At the time, that represented a staggering 19 million women.
When Allsworth broke down the data by race, only 23 percent of white women were positive for BV, compared with nearly one-third of Mexican American women and over half of African American women.
Her analysis also showed that BV rates were higher in women whose education had stopped at or before high school, and in women whose family income was near or below the federal poverty level. The infection was much more common in women who had douched in the last six months—and, somewhat surprisingly, it was present in 15 percent of women who reported never having had sex.
That shows that BV is a “natural process” on some level, says Allsworth, now at the University of Missouri-Kansas City School of Medicine. Even so, she calls the much higher rates of BV in certain groups “pretty shocking.” What might account for these differences? She says we don’t know yet, but she suspects it has a lot to do with social networks: “Whose microorganisms do you come in contact with?”
It’s still unclear if unprotected sex is always a BV risk or if it depends on having a partner with a certain bacterial profile, says Allsworth. The changes in vaginal bacteria that result from sex are natural, “but we really don’t understand how to support the disrupted vagina and get it back to a healthy state,” she says. “We don’t even really know what ‘healthy’ is.”
And, Allsworth notes, the work raises more questions than it answers: Have the women without a dominant Lactobacillus never had it or did they lose it somehow? What is it about certain bacterial cocktail parties that create an advantage for BV?
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Another huge health inequality plays out across the Atlantic. In Africa, black women living in poverty face the burden of both BV and HIV. As among African American women in the U.S., BV is common: Around 38 percent of women in Kenya, Rwanda, and South Africa had it in a 2014 study. Many women in Africa practice traditional vaginal washing, deodorizing and tightening that, like douching, make BV more likely.
BV puts women at increased risk of both acquiring and transmitting HIV. It’s been estimated that having full-blown BV or even simply an altered population of bacteria in the vagina (a precursor to BV) accounts for 29 percent of new HIV infections among women in Zimbabwe and Uganda. In 2012, Craig Cohen, now a professor of obstetrics, gynecology, and reproductive sciences at the University of California, San Francisco, led a team that followed more than 2,200 African couples and discovered that having BV tripled a woman’s chances of transmitting HIV to her uninfected male partner.