As word spread that Miami's hippest neighborhood was now considered ground zero for the first mosquito-transmitted infections of the Zika virus in the U.S. mainland, many residents vowed to take precautions, local officials urged tourists not to change travel plans and mosquito-control workers geared up for war against the pests.

"Zika is now here," Dr. Thomas Frieden, director of the U.S. Centers for Disease Control and Prevention, said Friday.

Some Miami residents said Friday that they were stocking up on mosquito repellent and planning to bring lunches to work instead of sitting at outdoor cafe tables under the Wynwood neighborhood's bright murals. The gentrifying neighborhood is known for bold graffiti-style murals spray-painted across warehouses, art galleries, restaurants and boutiques.

"I'm freaking out ... but at the same time I don't want to freak out," said Wynwood resident Zoe Schultze as she cradled her 6-month-old son in her arms while she stopped for coffee with her husband.

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U.S. health officials said they do not expect widespread outbreaks in this country of the sort seen in Brazil, and other parts of Latin America and the Caribbean, in part because of better sanitation, better mosquito control and wider use of window screens and air conditioners.

The virus has triggered alarm across the warmer latitudes of the Western Hemisphere. Although most people who get Zika don't even know they are sick, infection during pregnancy can cause babies to be born with disastrously small heads and other severe brain-related defects.

Some medical experts said pregnant women should not travel to the Miami area, especially if it involves spending time outdoors. However, the CDC is not issuing such advice.

"If I were a pregnant woman right now, I would go on the assumption that there's mosquito transmission all over the Miami area," warned Dr. Peter Hotez, a tropical medicine expert at the Baylor College of Medicine.

He said that there are probably more cases that have not been diagnosed and that people should not be surprised if mosquitoes are soon found to be spreading Zika in Louisiana and Texas as well.

More than 1,650 people in the mainland U.S. have been infected with Zika in recent months, nearly all while traveling abroad. The four people in Florida are believed to be first ones to contract the virus from mosquitoes within the 50 states.

"This is not just a Florida issue; it's a national issue. We just happen to be at the forefront," Florida Gov. Rick Scott said.

People in Florida's Miami-Dade and Broward counties are being tested to learn whether there are more cases, the governor said.

Even though the mosquito-transmitted cases were limited to South Florida, leaders across Florida were nervous about the potential fallout to tourism, the state's No. 1 industry.

Florida had more than 106 million visitors last year, and tourism-related employment accounts for around 1.2 million jobs.

No mosquitoes in Florida have actually been found to be carrying Zika, despite the testing of 19,000 by the state lab. But other methods of Zika transmission, such as travel to a stricken country or sex with an infected person, have been ruled out in the four South Florida cases.

It's not surprising that no mosquitoes have tested positive because it can take a couple of weeks before an infected person shows symptoms, and by then the mosquitoes that transmitted the virus are dead, said C. Roxanne Connelly, a medical entomology specialist at the University of Florida and a past president of the American Mosquito Control Association.

"Believe it or not, it's difficult to find positive mosquitoes even when you're in the middle of an epidemic," Connelly said. "Sometimes you don't know where these people were infected. At home? At work? Where they were playing baseball?"

Zika-fighting efforts include pesticide spraying, setting of traps and eliminating standing water around homes.

Jenny Gray, who is 27 and works in Wynwood for an art designer, said she will follow experts' advice to wear insect repellent.

"I don't plan on having kids now, but I do sometime in the future. Better to stay protected," she said. "That really does concern me."

But Phillip Lopez, a 34-year-old Wynwood resident who works at an outdoor bar and exercises outside, said: "It's a concern, but you got to do what you got to do. You can't not go outside."