Florida officials confirmed that the first continental U.S. cases of Zika virus were transmitted by mosquitoes.
Health officials said on July 29 local mosquitoes infected four individuals in the Miami-Dade and Broward counties, CNN reports.
"While no mosquitoes trapped tested positive for the Zika virus, the department believes these cases were likely transmitted through infected mosquitoes in this area," the Florida Department of Health said in a statement.
Dr. Tom Frieden, director of the Centers for Disease Control and Prevention, agreed and elaborated further: "All the evidence we have seen indicates that this is mosquito-borne transmission that occurred several weeks ago."
While the CDC said there have been 1,658 cases of the virus reported in the continental U.S., none of those were transmitted by local mosquitoes.
Zika can be transmitted in other ways, such as through sexual activity, according to experts.
“[This] is the news we've been dreading," said Dr. Edward McCabe, chief medical officer and senior vice president of the March of Dimes. "It's only a matter of time before babies are born with microcephaly, a severe brain defect, due to local transmission of Zika in the continental U.S. Our nation must accelerate education and prevention efforts to save babies from this terrible virus."
More than 400 women in the continental U.S. have been infected. However, the relationship between the virus and microcephaly is not yet fully clear.
"The experts agreed that a causal relationship between Zika infection during pregnancy and microcephaly is strongly suspected, though not yet scientifically proven," WHO director-general Dr. Margaret Chan said.
In February, WHO declared the virus a "public health emergency of international concern.”
Still, federal, state and local officials are investigating further, and asking other residents in the respective Florida counties for urine samples to see if anybody else may have the virus.
Authorities say it's likely local mosquitoes might have infected others without them knowing. Eighty percent of those with the virus display no symptoms, which include red eyes, fever, joint pain and rashes that can last from a few days to one week.
In the meantime, blood donations have been halted.
"[It is] a prudent measure to help assure the safety of blood and blood products,” the FDA explained in a July 28 statement.