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Little Threat of Zika Spread From Rio Olympics: Study

Because it's winter in Brazil, mosquito activity has subsided

By Dennis Thompson
HealthDay Reporter

MONDAY, July 25, 2016 (HealthDay News) -- Travelers and competitors at the 2016 Olympic Games in Brazil are not likely to contract the Zika virus during their stay or bring it back to their home countries, Yale University experts contend in a new report.

Fear of the mosquito-borne virus has led some athletes to skip the games, which start Aug. 5 in Rio de Janeiro. U.S. cyclist Tejay van Garderen withdrew from Olympic consideration because of the potential effects Zika infection could have on his pregnant wife. And a number of golf stars -- including Jason Day, Rory McIlroy, Dustin Johnson, Jordan Spieth, Adam Scott, Louis Oosthuizen and Vijay Singh -- have also declined to participate.

But out of as many as 500,000 travelers to Rio for the games, estimates state that at most 37 people are likely to contract Zika and return home while still contagious, said study co-author Gregg Gonsalves.

"Yes, Zika is an epidemic. Yes, we need to invest in combating Zika," Gonsalves said. "But we need to make policy based on the best available evidence and not overstate our case."

Gonsalves is co-director of the Global Health Justice Partnership, a joint program of Yale Law School and Yale School of Public Health in New Haven, Conn.

The report supports the position taken by the World Health Organization. The WHO has said the Rio Olympics are not expected to play any significant role in the international spread of Zika.

"Based on several modeling studies, the risk to non-pregnant visitors or competitors to the Olympics seems to be manageable and does not merit any postponement or abstention," said Dr. Amesh Adalja, a senior associate at the University of Pittsburgh's UPMC Center for Health Security in Baltimore. "It is more likely, by some estimates, that visitors to the Olympics will contract influenza than Zika."

The Zika virus is frightening because it can cause the brain-related birth defect microcephaly if an expectant mother becomes infected.

Microcephaly results in babies born with abnormally small heads and brains. Thousands of babies have been born with microcephaly in Brazil, the epicenter of the Zika epidemic, according to the WHO.

However, Zika poses little threat to most other people. In fact, an estimated 80 percent of people who come down with Zika don't know they've been infected, according to health experts.

What's more, it's winter in Brazil, which means mosquito activity has subsided for the year, the new study points out. Also, most travelers will stay in screened and air-conditioned lodgings, further reducing their potential exposure to mosquitoes.

According to the Yale experts, other factors that will minimize the risk of Zika spread from the Olympics include:

  • Zika infection clears the human body within 10 days, meaning people who become infected will likely not be contagious by the time they head home.
  • More than half of Olympic visitors are expected to return to wealthy first-world countries where there's little risk of establishing local transmission of Zika.
  • About another third of Olympic visitors will return to Latin America countries where Zika transmission is already established, and so won't contribute to the epidemic.

Overall, the Yale experts estimate anywhere from six to 80 Zika infections in travelers to the Olympic Games, with just one to 16 of those people experiencing any symptoms.

"If I could get a ticket to the Olympics, I would go to the Olympics," Gonsalves said. "I personally wouldn't feel worried at all about going down there."

By the time they're ready to go home, only between three and 37 of the infected visitors are expected to still be contagious, the study authors concluded. The rest will have cleared the virus from their bodies.

People traveling to Brazil know they're entering the world's most active Zika area. And, that will influence their decision to attend and their actions while there, said Stephen Higgs, director of the Biosecurity Research Institute at Kansas State University.

"The types of people who are visiting are going to already have taken the threat seriously when they made the decision to go to Rio," Higgs said. "They're not the people who are going to be in the back streets, where mosquito control isn't being implemented as effectively as possible."

For example, pregnant women are not expected to attend the Olympic Games, since their unborn children bear the brunt of the risk from a Zika infection. The WHO and the U.S. Centers for Disease Control and Prevention have advised pregnant women against traveling to any country or region where Zika is actively transmitted.

"They're no more likely to get the virus than anybody else, but the consequences of them getting the virus are much worse than for anybody else," Higgs said.

The report was published July 25 in the Annals of Internal Medicine.

More information

For more on Zika virus, visit the U.S. Centers for Disease Control and Prevention.

This Q&A will tell you what you need to know about Zika.

To see the CDC list of sites where Zika virus is active and may pose a threat to pregnant women, click here.


SOURCES: Gregg Gonsalves, M.Phil., lecturer, Yale Law School and co-director, Global Health Justice Partnership; Amesh Adalja, M.D., senior associate, University of Pittsburgh's UPMC Center for Health Security, Baltimore; Stephen Higgs, Ph.D., director, Biosecurity Research Institute, Kansas State University; July 25, 2016, Annals of Internal Medicine

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