It's rare but definitely not impossible for HIV to be transmitted by sexual contact between women, according to a paper published this week by the Centers for Disease Control and Prevention. In the first confirmed case of its kind, the CDC believes one Texas woman infected another with HIV through sexual activity that included unprotected sex, the use of sex toys, and sexual contact while menstruating, reports the Los Angeles Times. The women, both in their 40s, had been in a monogamous relationship for six months before the infection, which was first detected in early 2012.
Other risk factors including IV drug use were absent, and it had been at least 10 years since the newly infected woman had sex with a man. Further, the paper notes that "the viruses infecting the two women had [greater than or equal to] 98% sequence identity in three genes." While it's not the first time such a transmission has been "suspected ... not all the pieces were there to say it so clearly as this one," an epidemiologist tells NPR, saying the case should serve as a warning that many kinds of sexual interaction can spread the virus. "Anytime there's intimate contact—even through the use of sex toys—prevention measures should be taken, especially when there's a chance of blood contact," he says.