(CNN) Men exposed to the Zika virus and who have a pregnant partner should use a condom or abstain from sex until the baby is born, the Centers for Disease Control and Prevention advised Friday in guidelines aimed at preventing sexual transmission of the virus.

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."

Photos: Zika virus outbreak Photos: Zika virus outbreak A pest control worker fumigates a school corridor on the eve of the annual national Primary School Evaluation Test in Kuala Lumpur on Sunday, September 4. Malaysia reported its first locally transmitted Zika case on September 3. Hide Caption 1 of 29 Photos: Zika virus outbreak A banner about Zika virus is seen as ferry passengers arriving from Singapore get in line at the immigration check on September 4, in Batam, Indonesia. Hide Caption 2 of 29 Photos: Zika virus outbreak A banner is flown over the South Pointe Park area, Tuesday, September 6, in Miami Beach, Florida. Hide Caption 3 of 29 Photos: Zika virus outbreak A pest control worker fumigates drains at a local housing estate where the latest case of Zika infections were reported on Thursday, September 1, in Singapore. Hide Caption 4 of 29 Photos: Zika virus outbreak Florida Gov. Rick Scott and Florida Surgeon General Dr. Celeste Philip address the media gathered at the Miami-Dade County Department of Health as they announce five cases of Zika in a 1.5 mile area of Miami Beach on Friday, August 19, in Miami, Florida. Hide Caption 5 of 29 Photos: Zika virus outbreak Brazil's interim President Michel Temer, center right, meets with officials during Temer's first visit to the Olympic Park on Thursday, June 14, in Rio de Janeiro. The Rio 2016 Olympic Games commence August 5 amid a political and economic crisis in the country along with the Zika virus outbreak. Hide Caption 6 of 29 Photos: Zika virus outbreak Rio 2016 Chief Medical Officer Joao Grangeiro, Municipal Secretary of Health Daniel Soranz and Sub-secretary of the State for Health and Surveillence Alexandre Chieppe field questions from the media during an International Media Briefing to address the Zika virus on Tuesday, June 7, in Rio de Janeiro. Hide Caption 7 of 29 Photos: Zika virus outbreak A health worker fumigates an area in Gama, Brazil, to combat the Aedes aegypti mosquito on Wednesday, February 17. The mosquito carries the Zika virus, which has suspected links to birth defects in newborn children. The World Health Organization expects the Zika outbreak to spread to almost every country in the Americas. Hide Caption 8 of 29 Photos: Zika virus outbreak A man places a mosquito net over a bed at a home for the elderly in Masaya, Nicaragua, on Thursday, February 11. Hide Caption 9 of 29 Photos: Zika virus outbreak An Aedes aegypti mosquito floats in stagnant water inside a tire at a used tire store in Villavicencio, Colombia, on Thursday, February 4. Hide Caption 10 of 29 Photos: Zika virus outbreak A health worker fumigates an area in Caracas, Venezuela, on Tuesday, February 2. Hide Caption 11 of 29 Photos: Zika virus outbreak A lab worker exposes his arm to Aedes aegypti mosquitoes during testing at the Roosevelt Hospital in Guatemala City, Guatemala, on Monday, February 1. Hide Caption 12 of 29 Photos: Zika virus outbreak Tainara Lourenco sits inside her home in Recife, Brazil, on Friday, January 29. Lourenco, five months pregnant, lives at the epicenter of Brazil's Zika outbreak. The Zika virus has been linked to microcephaly, a neurological disorder that results in newborns with small heads and abnormal brain development. Hide Caption 13 of 29 Photos: Zika virus outbreak Dr. Angela Rocha shows brain scans of a baby born with microcephaly at the Oswaldo Cruz Hospital in Recife on Thursday, January 28. Hide Caption 14 of 29 Photos: Zika virus outbreak Alice Vitoria Gomes Bezerra, a 3-month-old baby with microcephaly, is placed in her crib by her father Wednesday, January 27, in Recife. Hide Caption 15 of 29 Photos: Zika virus outbreak A health ministry employee fumigates a home in Soyapango, El Salvador, on January 27. Hide Caption 16 of 29 Photos: Zika virus outbreak A lab technician at the Oswaldo Cruz Foundation Institute stores Aedes aegypti mosquitoes to be used in research in Recife on January 27. Hide Caption 17 of 29 Photos: Zika virus outbreak A patient suffering from Guillain-Barre syndrome recovers at a hospital in San Salvador, El Salvador, on January 27. Researchers are looking into a possible link between Zika and Guillain-Barre, a rare disorder that causes the body's immune system to attack its nerves. Hide Caption 18 of 29 Photos: Zika virus outbreak Luiz Felipe lives in Recife and is one of more than 4,000 babies in Brazil born with microcephaly since October. The drought-stricken impoverished state of Pernambuco has been the hardest-hit, registering 33% of recent cases. Hide Caption 19 of 29 Photos: Zika virus outbreak A health worker sprays insecticide under the bleachers of Rio de Janeiro's Sambadrome on Tuesday, January 26. Hide Caption 20 of 29 Photos: Zika virus outbreak A Brazilian soldier inspects a home in Recife on Monday, January 25, while canvassing the neighborhood and attempting to eradicate the larvae of mosquitoes linked to the virus. Hide Caption 21 of 29 Photos: Zika virus outbreak David Henrique Ferreira, a 5-month-old who has microcephaly, is watched by his brother in Recife on January 25. Hide Caption 22 of 29 Photos: Zika virus outbreak The larvae of Aedes aegypti mosquitoes are photographed in a lab in Cali, Colombia, on January 25. Scientists are studying the mosquitoes to control their reproduction and resistance to insecticides. Hide Caption 23 of 29 Photos: Zika virus outbreak Angelica Prato, a pregnant woman infected by the Zika virus, receives medical attention at a hospital in Cucuta, Colombia, on January 25. Hide Caption 24 of 29 Photos: Zika virus outbreak A woman walks through fumes as health ministry employees fumigate an area in Soyapango on Thursday, January 21. Hide Caption 25 of 29 Photos: Zika virus outbreak Brazilian soldiers apply insect repellent as they prepare for a cleanup operation in Sao Paulo on Wednesday, January 20. Hide Caption 26 of 29 Photos: Zika virus outbreak A researcher at the University of Sao Paulo holds a container with female Aedes aegypti mosquitoes on Monday, January 18. Hide Caption 27 of 29 Photos: Zika virus outbreak A graveyard in Lima, Peru, is fumigated on Friday, January 15. Hide Caption 28 of 29 Photos: Zika virus outbreak Aedes aegypti mosquitos are seen at the University of Sao Paulo on January 8. Researchers from the Pasteur Institute in Dakar, Senegal, came to Brazil to train local researchers to combat the Zika virus epidemic. Hide Caption 29 of 29

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.