U.S. Olympic athletes will have to decide themselves on whether to travel to Brazil for this year's Summer Games despite the risk of the Zika virus, officials said on Monday, as some competitors admitted they were worried about the risk.

The mosquito-born virus, linked to a spike in the rare birth defect microcephaly, has hit Brazil hard and has spread through much of Latin America and the Caribbean, raising concerns for athletes planning to compete in August in Rio De Janeiro, particularly those thinking of having children after the Games.

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The U.S. Olympic Committee will provide athletes with mosquito nets and bug spray and is considering bringing additional medical staff to deal with concerns around the illness, USOC chief executive Scott Blackmun told reporters in Los Angeles on Monday.

"It is going to be up to each individual athlete to make his or her decision," Blackmun said, referring to the expected 550 U.S. competitors. "We don't want to be in the business of making health policy."

The committee on Friday formed a group of three volunteer medical advisors to protect U.S. athletes and Olympic staff from infectious diseases including Zika while in Rio. Two of those doctors are women, Blackmun said, noting that organizers are aware Zika poses the greatest risk to women who could become pregnant.

"I'm not aware of a single athlete that has made a decision not to attend because of conditions in Rio," Blackmun said.

While voicing confidence in the steps the USOC and Rio organizers are taking to address Zika, some athletes admitted they remained worried.

Golfer Stacy Lewis, 31, said she was worried about Zika.

"I'm a little bit worried - for sure," Lewis said. "I don't think I can sit here and say I'm not going to go if it gets bad. I think you have to see how things play out, but it's definitely a concern."

Runner Alysia Montano, 29, who famously raced in the 800 meters at the 2014 U.S. national championships while eight months pregnant, also voiced concerns.

"Having started my family and wanting to expand sometime in the future, it is of great concern," Montano said. "I'm a mom now and worry sometimes rises to the top."

Brazilian and Olympic officials have sought to dispel some concerns about Zika by saying that August - mid-winter in the southern hemisphere - is typically a time when there are fewer mosquitoes in Rio.

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Much remains unknown about Zika, including whether the virus actually causes microcephaly in babies, a condition defined by unusually small heads that can result in developmental problems. Brazil said it has confirmed more than 640 cases of microcephaly, and considers most of them to be related to Zika infections in the mothers. Brazil is investigating more than 4,200 additional suspected cases of microcephaly.

Scientists are predicting that Zika could spread to every country in the Americas but Canada and Chile.

"This is not just a problem in Brazil," Blackmun said. "This is a problem in the Americas."