HOUSTON -

A Houston doctor says one of his female patients contracted HIV from sexual contact with another woman.

A new twist was revealed Friday in the battle against HIV and AIDS. For the first time ever, doctors believe there is new proof that HIV can be sexually transmitted between two women -- and those women live in Houston.

"In 34 years of investigating HIV infection, this is the first time anybody has ever identified sexual transmission between two women," said Kathy Barton, with the Houston Department of Health and Human Services.

The Centers for Disease Control issued a report Friday claiming a Houston woman, who'd been HIV positive for years, transmitted the virus to her monogamous girlfriend through unprotected sex.

"This is a very unique case in that the newly infected person was a regular blood donor. So we had a long history of her negative status for many years," said Barton.

That status changed in the summer of 2012 after blood bank testing revealed the woman had tested positive for HIV, the virus that can cause AIDS.

The Houston Department of Health was notified and that kicked off a nearly two year investigation.

"The CDC was able to serial type both of their viruses and were able to determine it was the same virus," said Barton.

All other forms of transmission were carefully ruled out.

According to the reports, the woman who originally had HIV had stopped treatment in 2010.

"If she stopped treatment, then the amount of virus circulating in her blood stream could and probably would elevate. So not being on medicine definitely increases the risk and the chance of transmission," said Dr. Robin Hardwicke of the University of Texas Health Medical School.

Experts say this news should serve as an important lesson.

"Women think if they're only having sex with other women, that they're safe from sexually transmitted diseases. But they're not safe," said Hardwicke.

Privacy laws prohibit revealing the patient's identity, but we do know that the woman who contracted the virus from her partner is 46 years old and living in Houston.