Officials also said that pregnant women who have been exposed to Zika should talk with their doctors about testing for the virus.
While saying that the situation with Zika is "evolving rapidly" and that much had been learned in just the past two weeks, CDC Director Dr. Tom Frieden stressed in a news briefing that the primary concern with Zika at this time is protecting pregnant women and their unborn babies from a neurological disorder known as microcephaly.
"Each passing day, the linkage between Zika and microcephaly becomes stronger," Frieden said. Microcephaly results in babies being born with abnormally small heads that can lead to severe development delays and even death.
Since November, Brazil has seen 404 confirmed cases of microcephaly in newborns. Seventeen of those cases have a confirmed link to the Zika virus. Fifteen babies have died from the condition, with five linked to Zika. An additional 56 deaths are under investigation, and authorities are investigating 3,670 suspected cases.
"The priority is protecting pregnant women," Frieden told CNN Chief Medical Correspondent Dr. Sanjay Gupta in an interview. "If you're pregnant, and you're thinking about traveling to a place were Zika is spreading, please don't.
"If you live in an area where Zika is spreading and you're pregnant, please protect yourself against mosquitoes. That's the bottom line."
Guidance for pregnant women without symptoms
Two weeks ago, the CDC advised any pregnant woman with symptoms of Zika (which can be mild and include fever, rash, headache, red eye) to be tested for the virus. Friday, the agency added guidelines for pregnant women who fear they have been exposed to the virus but have no symptoms.
"We know that four out of five people with Zika will have no symptoms," Frieden said in the briefing. "So our new guidance says pregnant women without symptoms can be offered testing between two to 12 weeks after travel."
Those tests would be serological blood tests, in addition to the ultrasounds recommended in the CDC's first round of guidance. "We heard that serial ultrasounds were very challenging to the health community, so we are now rolling out blood test kits," Frieden said.
He said that while the CDC is working around the clock to produce these kits, "not everyone who wants a test will be able to get one at this time" and that some of the tests might produce a false positive.
"They are not perfect, no test is perfect, but they are performing better than we had hoped, so we have more confidence than two weeks ago," said Frieden.
As for women who are thinking about getting pregnant, "We wish we had a perfect test to determine if someone might be potentially infectious, but we don't," Frieden said. "So the tests we are rolling out are being prioritized for women who are currently pregnant."
CDC issues guidelines for male sexual partners
Frieden also announced new guidelines for men who have partners who are pregnant.
"Men who live in or travel to areas of active Zika infections and who have a pregnant sexual partner should use latex condoms correctly, or refrain from sex until the pregnancy has come to term," Frieden told CNN's Gupta, "or until a test is available to see if he could possibly infect her."
While a study that showed Zika only stayed viable in blood and saliva for a week, "We don't know how long Zika can persist in semen," Frieden said. "We're doing those tests now, but it could be weeks to months before we have an answer.
"That's why we've issued these guidelines now, specifically for male sexual partners of women who are pregnant."
And for women who are not pregnant, Frieden told Gupta, "You can have a conversation with your doctor, but keep the big picture in mind. For most people who get Zika, there are no symptoms at all. For those who with symptoms, they are usually mild and gone within a week."
He said that risk for developing Zika depends on how long a person was in the area where Zika is present, how many mosquitoes are active in that area, how many mosquito bites they had and how well they protected themselves.
No ban on kissing, CDC says
Also on Friday, a Brazilian public health institute said active Zika virus has been detected in saliva and urine. The finding poses new questions for researchers trying to understand how the virus could spread.
"It was known that the virus could be present in both urine and saliva. This is the first time we've demonstrated that the virus is active [in those fluids], with the potential to cause infection," Fiocruz researcher Myrna Bonaldo said.
But it doesn't necessarily mean you can get sick from contact with an infected person's saliva or urine, Gupta said.
"People have already shown that it can spread to bodily fluids other than blood, so this isn't entirely surprising," he said. "Presence of virus in saliva doesn't mean that it's necessarily transmissible that way."
Other labs, including the CDC, must now confirm the Fiocruz finding, Gupta said.
"We are not issuing guidance on kissing," Frieden said in the news briefing. "We take all reports seriously, but we need more information including the methodology of the study. The bottom line is Zika is primarily a mosquito-borne disease."
The World Health Organization on Monday declared a public health emergency
over the Zika virus and increased reports of birth defects and a serious neurological condition that could be linked to it.
Health officials had previously reported isolated instances of the virus being passed via blood transfusions and sexual contact, including a U.S. case
reported this week. The virus has spread to at least 29 countries.
As many as 3 million to 4 million people across the Americas will be infected with the virus in the next year, WHO has estimated.
Reports of Guillan-Barre Syndrome, a neurological conditon that can lead to paralysis, have also risen in areas where the virus has been reported.
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