Though documented cases of HIV transmission between women aren't common, the Centers for Disease Control and Prevention announced Thursday that such an instance did occur in Houston in 2012.

In 2006, there had been "no confirmed cases of female-to-female sexual transmission of HIV in the United States database." Today, women who have sex with women aren't even mentioned on the CDC's website under information on "HIV Among Women." According to the CDC's Morbidity and Mortality Weekly Report, the two women in this case had been in a monogamous relationship for six months. When the DNA sequences of their viruses were compared, they almost perfectly matched. This indicates that the virus was likely not transmitted via a different source than sex the two of them had together:

The potential for HIV transmission by female-to-female sexual contact includes unprotected exposure to vaginal or other body fluids and to blood from menstruation, or to exposure to blood from trauma during rough sex. Other potential exposures associated with HIV transmission in WSW that must be ruled out include injection drug use (IDU), heterosexual sex, tattooing, acupuncture, piercing, use of shared sex toys between the partners and other persons, exposure to body fluids of others, and receipt of transplants or transfusion.

It appears that the way the HIV-positive woman gave the virus to her partner was through routine unprotected sex, as other "risky" behaviors were ruled out. "They described their sexual contact as at times rough to the point of inducing bleeding in either woman," reports the CDC. "They also reported having unprotected sexual contact during the menses of either partner."

While this case doesn't suggest that the risk factor for women who have sex with women is any higher than it was known to be before, it's a helpful reminder that no one is immune to STIs, as Amy Lansky, a deputy director at the CDC's Division of HIV/AIDS Prevention told NPR's "Shots" blog. "'s important for discordant lesbian couples — when one is HIV positive and the other is negative — to get medical counseling and HIV treatment," she said. This case also makes recent news of a potential gel that could help women protect themselves against HIV seem particularly timely.


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