On Wednesday, the Florida Department of Health increased the number of suspected nontravel-associated Zika cases under investigation in the state to four, according to CNN.
Half of the cases are in Miami-Dade County and the other two are in Broward County. None of the infected individuals have traveled to regions with active local Zika transmission, though sexual transmission has yet to be ruled out.
Mara Gambineri, communications director for the Florida Department of Health, told CNN via email, "We are looking into other modes of transmission. We're conducting this investigation as we would other mosquito-borne viruses, such as dengue."
To confirm local transmission, epidemiologists are surveying neighboring households and asking residents to provide urine samples to determine how many people may have become infected with the virus. The possibility of residents who have Zika but don't know it is heightened by the fact that 80 percent of those who have Zika display no symptoms.
"Evidence is mounting to suggest local transmission via mosquitos is going on in South Florida," Tom Skinner, senior press officer at the CDC, wrote in an email to CNN. "These cases fit similar transmission patterns [of] mosquito-borne diseases like chikungunya that we've seen in South Florida in years past."
As of agency's July 20 update, the CDC has tallied more than 1,400 cases of Zika in the U.S. with 400 of said cases occurring in pregnant women. Additionally, 12 infants in the U.S. have been born with Zika-related birth defects like microcephaly.
If these cases are confirmed as homegrown, they would be the first locally acquired cases in the U.S. and establish that Zika is being transmitted by Florida mosquitoes.
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