A 46-year-old woman "likely acquired" human immunodeficiency virus while in a monogamous relationship with an HIV-positive female partner in Texas, said the Centers for Disease Control and Prevention, Newsmax Health reports.

The woman, whose name was not released, had engaged in heterosexual relationships in the past, but not in the 10 years prior to her HIV infection.

Her HIV-positive partner, a 43-year-old woman who first tested positive in 2008, was her only sexual partner in the six months leading up to the test that came back positive for HIV.

She did not report any other risk factors for acquiring the virus that causes AIDS, such as injection drug use, organ transplant, tattoos, acupuncture or unprotected sex with multiple partners.

The strain of HIV with which she was infected was a 98 percent genetic match to her partner's, said the CDC in its weekly report.

The couple said they had not received any counseling about safe sex practices, and reported that they routinely had sex without barrier methods.

"They described their sexual contact as at times rough to the point of inducing bleeding in either woman," said the CDC report.

"They also reported having unprotected sexual contact during the menses of either partner."

The CDC warned that although such cases are rare, "female-to-female transmission is possible because HIV can be found in vaginal fluid and menstrual blood."