The U.S. Food and Drug Administration has ordered blood banks in Florida's two most densely populated counties to stop collecting blood as health officials determine whether Zika has begun transmission in the continental United States.
Florida has been investigating four possible cases of local transmission in Miami-Dade County and Broward County. It is the first U.S. state to report cases that may not be related to travel to other countries with active outbreaks.
Zika has struck hardest in Brazil, where the outbreak was first detected last year, and has since spread rapidly through the Americas. The virus can cause a rare birth defect, microcephaly, in newborns whose mothers have been infected, and is believed to be linked to Guillain-Barre syndrome in adults.