The unnamed woman “engaged in a single event of condomless vaginal intercourse with a male partner the day she returned to NYC from travel to an area with ongoing Zika virus transmission,” according to Alexander Davidson, MPH, and colleagues in the city’s Department of Health and Mental Hygiene, during which she had already begun to show symptoms of infection.

A week later, the male partner also developed Zika symptoms, including fever, rash, joint pain, and conjunctivitis, the officials said in an early online release from Morbidity and Mortality Weekly Report. By this time, the woman had already tested positive for Zika infection, and subsequent testing in the man confirmed that he, too, had contracted the virus.

Because the man appeared to have no other opportunity to acquire the infection, Alexander and colleagues concluded that it must have been transmitted during the sex act.

“This case represents the first reported occurrence of female-to-male sexual transmission of Zika virus,” the researchers wrote in MMWR.

They noted that other studies had identified the virus in the genital tract of infected women, and called for more research “to determine the characteristics of Zika virus shedding in the genital tract and vaginal fluid of humans.”

Infectious disease specialists contacted by MedPage Today said they weren’t surprised by the report.

We were anticipating that female-to-male transmission of Zika virus infection likely would be documented at some time and this is a convincing, rigorously investigated episode,” said William Schaffner, MD, of Vanderbilt University in Nashville.

The CDC, which publishes MMWR, said it is “currently updating recommendations for sexually active people in which the couple is not pregnant or concerned about pregnancy and for people who want to reduce personal risk of Zika infection through sex.”

To inform such recommendations, research should focus on the duration of female-to-male transmission risk, said Robert T. Schooley, MD, of the University of California San Diego. “We don’t know how long the virus is able to persist in the female genital tract and/or urine,” he noted.

Gary L. Simon, PhD, of George Washington University in Washington, speculated that it may become advisable to test everyone who visits endemic areas, irrespective of symptoms, “since 80% of Zika is asymptomatic.”

The MMWR report did not address the clinical course of either individual’s infection beyond the initial symptoms, but previous reports have suggested that severe symptoms are rare in otherwise healthy people.

LAST UPDATED 07.15.2016