KELLY MCEVERS, HOST:
Whether Zika will spread beyond the two neighborhoods we just heard about is an open question. On Friday the director of the Centers for Disease Control and Prevention, Dr. Tom Frieden, suggested broader travel restrictions might be wise.
TOM FRIEDEN: Pregnant women and their sexual partners who are concerned about potential Zika virus exposure may also consider postponing non-essential travel to all parts of Miami-Dade County.
MCEVERS: That's because the virus is known to cause birth defects. It's still too soon to know with any precision how fast the virus is spreading. NPR's Michaeleen Doucleff reports on why.
MICHAELEEN DOUCLEFF, BYLINE: Health officials in Florida have been working hard to figure out where Zika is spreading. They've been going door to door and testing people. So far they think that 37 people have caught Zika in Florida, but the CDC's Frieden says they probably haven't found all the cases.
FRIEDEN: There are undoubtedly more infections that we're not aware of right now.
DOUCLEFF: Ira Longini at the University of Florida has been using computer models to estimate just how many cases are likely hiding out in the state.
IRA LONGINI: It's basically saying there are hundreds of infections already probably out there.
DOUCLEFF: And he says that number could grow in the next month or so. Worst case scenario...
LONGINI: There could be as high as a thousand infections by September 15.
DOUCLEFF: Because here's the thing about Zika. When you get it, you often don't know you have it. Longini says about 4 out of 5 people with Zika don't have any symptoms at all. Others have only mild symptoms for just a short time.
LONGINI: So a lot of people with Zika, even with some of the symptoms, may not go to a doctor to seek care.
DOUCLEFF: So most cases don't get detected. Longini has also used computer models to predict where Zika could show up next in the U.S. He says their top concern is Texas, which has about a 25 percent chance of having a small outbreak in the next month. Dr. Anthony Fauci at the National Institutes of Health told ABC News yesterday floods in Louisiana put the Gulf States at risk for Zika.
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ANTHONY FAUCI: I would not be surprised if we see cases in Texas and Louisiana, particularly now where you have the situation with flooding in Louisiana. There's going to be a lot of problems getting rid of standing water.
DOUCLEFF: Where mosquitoes that could carry Zika breed and thrive. Michaeleen Doucleff, NPR News.
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