Brazil, which is hosting the Olympics and the Paralympics, is at the epicenter of the rapidly evolving epidemic that has spread to nearly 50 countries, most of them in Latin America and the Caribbean.

A top WHO official also suggested during a media briefing Tuesday that reporting discrepancies may be one reason for the relatively few number of microcephaly cases reported so far in Colombia, despite that country's thousands of cases of Zika infection. Brazil, by contrast, has more than 1,500 cases of microcephaly or other severe birth defects linked to Zika infections, according to the WHO.

The data from Colombia has been a concern for global health agencies tracking the spread of the virus and its impact, said Bruce Aylward, who is in charge of WHO's outbreaks and emergencies. A regional director from WHO has been in talks with officials there "to try and understand and reconcile this," he said.

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While other countries are reporting data from live births as well as stillbirths and other pregnancy outcomes, Colombia is "reporting only live births," Aylward said. He said " other factors" could be affecting the reporting, such as the decisions women are making as they manage their pregnancies.

Microcephaly, a severe and rare condition characterized by abnormally small heads and underdeveloped brains, is seen as Zika's greatest health risk to a fetus.

The WHO meeting was called to discuss outbreak-related issues, including calls to delay or move the Olympics because of public health concerns over the virus. About 230 prominent physicians, bioethicists and scientists from around the world posted a letter last month urging Director-General Margaret Chan to exert pressure on Olympic authorities.

More than 8,500 citizens from Spain and various Latin American countries also signed a petition requesting that the WHO and the International Olympic Committee postpone the Olympic Games.

But other public health officials, including Tom Frieden, director of the U.S. Centers for Disease Control and Prevention, have said there is no public health reason to postpone or move the Games.

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Aylward said about 20 percent of the world lives in a Zika-affected region, and 30 percent of global travel already is "in and out of Zika-affected areas of the world." He said the proportion of travel affected by the Olympics, which is expected to draw up to 500,000 visitors, is "very marginal."

Aylward also sought to clarify a WHO recommendation issued last week about ways to avoid sexual transmission of the virus. As part of its overall guidance to avoid having babies with birth defects, the WHO said "men and women of reproductive age" living in Zika-affected regions should "be correctly informed and oriented to consider delaying pregnancy."

The guidance drew widespread attention because the WHO had not previously made such a recommendation. Aylward said Tuesday that the agency's intention was to provide clarification about one of the options. "It was misconstrued as a change in WHO advice, but it was not," he said. Pregnancy remains "very much an individual decisions," he said.

The WHO and other public health agencies, including the CDC, have said pregnant women should skip the Olympics. NBC “Today” show anchor Savannah Guthrie said last week that she is expecting her second child and will not be going to Rio.

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Pregnant women infected with the virus during their first trimester face as high as a 13 percent chance that their fetus will develop microcephaly, according to research published last month that analyzed data from one of the most affected areas in Brazil.