Public health workers are collecting blood samples from 300 people on Florida's Treasure Coast, where 18 cases of a mosquito-borne illness have been confirmed.
Starting Friday, blood samples will be collected from Rio and Jensen Beach neighborhoods where the outbreak appears to be concentrated. Randomly selected participants will be asked if they've recently suffered symptoms of dengue fever. They'll also be asked about their recent travel and about activities that might expose them to mosquitoes.
Health officials say all the confirmed cases were exposed to dengue in those neighborhoods. None of the patients had recently traveled internationally.
OneBlood, a blood collection agency, suspended its blood donation program in Martin and St. Lucie counties due to the risk of a dengue fever outbreak.
While the outbreak is north of South Florida, health officials in Miami-Dade and Broward Counties are working with their mosquito control departments to keep it from spreading.
"The mosquito lives here. We are at risk of having more cases of locally-acquired dengue," said Dr. Alvaro Mejia-Echeverry with the Miami-Dade Health Department. "This is a mosquito that doesn't live in the wild. It likes to live with you. It lives in your houses and the periphery of your house."
The first case of dengue fever in Miami-Dade County was reported in August.
Dengue is sometimes called "break bone fever" because of the severe joint pain it causes in extreme cases. Other symptoms include high fever, severe headache and a rash. It's uncommon in the U.S.