ATLANTA » Anyone who has traveled to an area affected by the Zika outbreak and who wants to start a family should reconsider doing so for at least six months after travel, federal health officials said today.

Warning that the Zika virus persists in semen longer than in blood, the Centers for Disease Control and Prevention issued its strictest guidelines yet on sexual contact.

“We previously focused on women who were already pregnant,” said Dr. Denise Jamieson, one of the doctors leading the CDC’s pregnancy and birth defects team as part of it’s Zika response. “Now this is concerning women who want to get pregnant.”

Though it is primarily transmitted by bites from mosquitoes commonly found in the Southern United States, Zika is also passed along through sexual contact by semen. In tests, the virus has persisted in semen for 62 days after the onset of the virus, which is long after it is undetectable in blood, the CDC reported Friday.

Researchers are still trying to figure out whether Zika lasts longer than two months in semen, but because the virus is believed to cause severe birth defects in fetuses at any stage of development, the CDC put out the new guidance Friday.

Men who have traveled to, or who live in, regions where a Zika outbreak is present should not have sex without a condom for six months if they have had any symptoms related to Zika, health officials said. Those symptoms include fever, sore joints, skin rash and conjunctivitis (red eyes). The condom requirement goes for all types of sexual activity, vaginal, oral or anal.

Yet, the majority of people who have Zika are asymptomatic. In those instances, for men who have had no symptoms of Zika, but who have traveled to a region in the midst of an outbreak, they should not have unprotected sex for at least eight weeks, the CDC said.

Similarly, women who have had Zika symptoms after traveling to an area with Zika should not try to get pregnant for at least six months after the onset of symptoms. That area now spans from Mexico to Puerto Rico to Brazil. Even if no symptoms are present, if a woman has been to any of those 39 countries or territories she should wait at least eight weeks before getting pregnant and even then should consult with her family doctor.

Jamieson said the safe-sex/abstinence windows were based on best guesses rather than hard data.

“There’s still so much we don’t know,” Jamieson said in a teleconference Friday. The guidelines represent “our best attempts to provide reasonable time frames based on what we know about how long the virus persists in semen and blood.”

So far, there have been six confirmed cases of sexual transmission of the virus in the contiguous U.S., though the men who passed the virus along to their partners had recently traveled to areas in the Americas with active Zika events. In the U.S., Puerto Rico has been the epicenter of the outbreak with 261 cases. The U.S. Virgin Islands has recorded 11 as of this week.

For the first time in the pandemic, the CDC guidelines regarding male sexual behavior, implicitly acknowledge male-to-male, as well as male-to-female sexual contact. During the teleconference however, CDC researchers did not say whether there is evidence that a man who has had sex with another man who has Zika could then pass it along to a female sexual partner.

“There’s still a lot we need to know to make evidence-based recommendations,” Jamieson said.

The new guidelines were announced just as many people around the United States are traveling for spring break, some to destinations in countries where the Zika pandemic has wreaked havoc. The link between the virus and the devastating birth defect microcephaly is becoming increasingly certain, researchers said. The defect, which is marked by an unusually small head, underdeveloped brain and cognitive disorders, can set a family up for years of emotional and financial stress.

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©2016 The Atlanta Journal-Constitution (Atlanta, Ga.)