3 more women in the US tested positive for Zika, but they probably didn't get it from mosquitoes

Three women, whose only risk factor was a male partner who had traveled to an area with an active Zika outbreak, have tested positive for the virus, according to a new report released by the US Centers for Disease Control and Prevention (CDC).

Earlier this week, the CDC said that it was investigating 14 suspected cases of Zika being sexually transmitted, in which a patient's only contact with the virus came from sex with a sick male partner who had traveled to an area with a high risk of infection.

According to the report, two of these cases are "laboratory-confirmed" and four more are "probable." Six other cases are still being investigated, and two have been ruled out.

'Only known risk factor'

All three cases involved men traveling in January to areas with active Zika transmission and returning home to the continental US to have unprotected sex with female partners. For all of the women, this was their "only known risk factor" for developing the virus. All three women showed symptoms of the virus and tested positive for Zika.

The CDC is still waiting for the men's test results.

Zika is most commonly transmitted through mosquito bites. Although infections are usually mild and cause symptoms in just 1 in 5 people, in pregnant women the virus may be linked to the severe birth defect microcephaly - an abnormally small head and underdeveloped brain.

Scientists recently reported that the virus can also affect tissues outside the brain and spinal cord, and has been linked to one reported stillbirth.

The first confirmed case of sexual transmission of Zika came in early February.

Meanwhile, the CDC has released the following guidelines for Zika and pregnant women.

CDC guidelines of Zika and sex

• Pregnant women and their male sex partners should discuss potential Zika exposure, including any history of Zika-like infection, with the woman's doctor.
• Men with a pregnant sex partner who have traveled or live in areas where the virus is being locally transmitted should consistently and correctly use condoms or abstain from sex during the pregnancy.
• All men who have traveled or live in areas with local Zika transmission who are worried about sexual transmission should consider using condoms or abstaining from sex.
• The CDC is currently investigating how long people infected with Zika can transmit the virus via sex. The virus persists for about a week in blood, but we don't know how long it stays in other bodily fluids like semen or saliva - though there have been reports of Zika virus in saliva samples.