But Clarisa Jimenez, the CEO of the Puerto Rico Hotel & Tourism Association, accused CDC of exaggerating the threat.
"From the very beginning the numbers that were given were based on projections. The reality is that as of today, less than half of 1 percent of the population has the virus," Jimenez told CNBC Thursday.
Frieden pushed back. "Unfortunately, when babies start to be born with microcephaly, that will change perceptions," he said.
"We projected, based on the chikungunya experience, that Zika might infect a quarter of the population in the first year and it is very much on track to do that," Frieden said.
Chikungunya is closely related to Zika and carried by the same Aedes mosquitoes. It's hardly ever deadly but extremely painful, so people remember getting it. Zika, on the other hand, doesn't cause symptoms in most people.
"People in Puerto Rico are saying Zika isn't like chikungunya," Frieden said. But he said it's just that people notice it less.
"There is a lot we don't know about Zika," Frieden added.
Armendariz said about a quarter of people infected in Puerto Rico are noticing Zika symptoms, including headache, rash, conjunctivitis and joint pain.
She's advising everyone to use mosquito repellent.
"I always say use it like perfume," she told NBC News. "Nothing replaces that."
"Wear light clothes, long sleeves, pants," she said, adding women should avoid sandals even though it's hot. She said pregnant women should make sure their partners use condoms. "You don't know if he has been bitten," she said. "If you are pregnant, protect yourself."