Health authorities in the United States said they were investigating 14 new reports of the Zika virus possibly being transmitted by sex, including to pregnant women. If confirmed, the unexpectedly high number would have major implications for controlling the virus, which is usually spread by mosquito bites.
Scientists had believed sexual transmission of Zika to be extremely rare. Only a few cases have ever been documented.
"We were surprised that there was this number," Dr. Anne Schuchat, the deputy director at the Centers for Disease Control and Prevention, said in an interview. "If a number of them pan out, that's much more than I was expecting."
Schuchat emphasized that only two of the infections have been confirmed, and that the information is still preliminary. But should the suspected infections be confirmed as real cases, that would open fresh complexity in the medical mystery of Zika, as scientists race to understand the disease and how to treat it.
In all, the United States has around 90 cases of Zika, which is believed to cause birth defects and a rare condition of temporary paralysis, according to the most recent count from the CDC. If confirmed, the cases of sexual transmission identified Tuesday would represent more than 10 percent of that total.
Officials at the CDC reported the potential cases in an alert to health care providers on Tuesday. In addition to the two confirmed cases, in four others the preliminary evidence suggests Zika, but the virus has not been confirmed, they said. The eight other cases are still being investigated. In all the cases, women in the continental United States had sex with men who had traveled to countries where the virus is circulating and the travelers reported symptoms within two weeks of the onset of their non-traveling female partner's symptoms.
The agency said that there is no evidence that women can transmit Zika virus to their sex partners, but added that more research is needed.