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MIAMI (CBSMiami) – U.S. officials are investigating more than a dozen new reports of sexually transmitted cases.

The Centers for Disease Control and Prevention (CDC) says it is investigating 14 new cases of the Zika virus being spread sexually. Several involve pregnant women.

The agency says in two of the new cases, the virus has been confirmed in women whose only known risk factor was sexual contact with a male partner who had recently traveled to a Zika hotbed.

“Mosquito-borne transmission is really the most common way the virus spreads but with these new suspected cases we are investigating; we are becoming more aware that sexual transmission may happen more often than we previously thought,” said Dr. Jennifer McQuiston, Deputy Incident Manager for CDC’s Zika Response.

The CDC recommends men who recently traveled to Zika-infected areas should use condoms or abstain from sex if their partner is pregnant or if the couple is concerned about transmitting the virus for any reason.

“It’s very important for pregnant women to recognize that sexual transmission of Zika is a possibility and to take the steps to protect themselves and their unborn babies,” said McQuiston.

Zika may be linked to the birth defect microcephaly which leaves newborns with abnormally small heads. But for women who aren’t pregnant, illness from the virus is usually mild. Eighty percent of infected people never have symptoms.

The CDC says it is unclear how long pregnant couples need to have protected sex. Research is underway to answer that question.