Florida Department of Health said they have gathered enough information as part of its ongoing investigation into non-travel related cases of Zika to conclude that "a high likelihood exists" that four cases are the result of local transmission.
At this time, the department believes that active transmission of the Zika virus are occurring in one small area in Miami-Dade County, in Florida, the statement said.
Florida has already seen nearly 400 cases of Zika, all involving people who were infected while traveling to parts of the world where the virus is circulating.
"While no mosquitoes have tested positive for the Zika virus," Florida Governor Rick Scott said, health department is aggressively testing people in this area to ensure there are no other cases.
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Florida Senator Marco Rubio said the news is disturbing.
"But no one should be surprised. I've been warning Congress for months that we would eventually have locally transmitted cases of Zika virus in the US, and sadly that has now become a reality," he said.