Zika could stay in the blood longer than scientists previously believed, according to the Centers for Disease Control and Prevention.
The CDC released updated guidance Monday on how to diagnose Zika and prevent sexual transmission of the virus, which increased from one to two weeks how long the agency thinks Zika can stay in the blood of a pregnant woman.
The updated guidance is aimed at helping doctors pin down whether a patient actually has Zika, which can be hard as only one in five people show symptoms of the virus.
Zika causes a mild illness that includes a fever and nausea, but it is also linked to the birth defect microcephaly.
Previously, scientists thought that the virus stays in a person’s blood for a week after symptoms occur.
“So the first week of illness was thought to be the best time to find evidence of the virus in blood using a Zika-specific test,” the CDC said. “But not everyone will see a health care provider while they are sick with Zika and many will not have symptoms.”
The agency has previously said it believes getting Zika in the first trimester of pregnancy poses the highest risk of the child contracting microcephaly, which causes the baby to be born with an abnormally small head.
CDC also updated recommendations for preventing the sexual transmission of Zika. The updated recommendation extends to sex between two women, and comes in the wake of a case of a woman infecting her female partner during sex.
CDC recommends that all pregnant women with a male or female partner who live in or traveled to an area where Zika is spreading use a condom or abstain from sex for the remainder of the pregnancy. All other couples with a partner who traveled to such an area should also use condoms or abstain from sex.
The updated recommendations come as the CDC is investigating two cases in Florida that are not travel-related.
So far there are more than 1,300 U.S. Zika cases. Except for about 14 sexually transmitted cases, all of the cases are from people who got the virus in a country where it is spreading via mosquitoes.
Mosquito bites are the primary way people get Zika, but so far there is no proof mosquitoes are spreading it directly in the U.S.
However, the CDC and local officials are investigating whether the two Florida cases could be the first mosquito-borne transmission in the country.
