NEW YORK (WABC) --The CDC on Friday confirmed New York City's first female-to-male sexual transmission of the Zika virus.
All previously reported cases of sexually-transmitted Zika virus infection have been spread from men to their sex partners.
The CDC recommends that all pregnant women who have a sex partner who has traveled to or resides in an area with Zika use barrier methods every time they have sex, or they should not have sex during the pregnancy.
Although no cases of woman-to-woman Zika transmission have been reported, these recommendations now also apply to female sex partners of pregnant women.
Zika is usually spread by mosquitoes, and health officials have known for some time that men can spread it through sex. The Centers for Disease Control and Prevention reported the case Friday and updated its advice for pregnant women.
The Zika virus causes only a mild illness, at worst, in most people. But infection during pregnancy can lead to severe brain-related birth defects for the fetus. The New York woman was not pregnant.
While this is the first documented case of a woman spreading Zika through sex, health experts say it is not surprising because most diseases that can be spread through sex can be spread by both men and women. It has likely been happening throughout the recent Zika outbreaks in Brazil, Latin America and elsewhere, though experts say it is probably not very common.
Last month, on the day the New York woman returned from a trip to a Zika-infected country, she had vaginal sex with her partner, without a condom, health officials were told.
She went to her doctor three days after her return, after developing common Zika symptoms such as fever, fatigue, rash and back pain. Tests showed Zika infection.
Seven days after they'd had sex, her male partner developed similar symptoms. Two days later, he went to the same doctor. The doctor tested him even though he hadn't traveled from a Zika outbreak area and no cases of female-to-male transmission had been reported. He tested positive for Zika.
They both are in their 20s, but no other details about them were released, including where the woman traveled. Both have recovered, a CDC official said.
The woman began menstruating the day after they had sex. Health official say she may have spread the virus through vaginal fluid or menstrual blood.
The primary concern about Zika infection is the virus's threat to pregnancies, and health officials have issued cautions to pregnant women who have a male sex partner who may have been infected.
Eleven countries, including the United States, have reported cases of apparent sexual transmission of Zika virus from one person to another, according to the World Health Organization.
(The Associated Press contributed to this report)