Health officials in Florida are investigating four cases of the Zika virus that don’t appear to be travel related.
The cases, detected in Miami-Dade County and Broward County, raise the possibility that mosquitoes in the US have begun to carry the virus, which has been linked to severe brain defects in newborns.
So far, cases outside of the Caribbean and Latin America have been attributed to people travelling to that region, or have been sexual transmitted.
According to the BBC, scientists will now investigate the Florida cases by carrying out door-to-door checks at households in an area within a 135-metre radius, which is the flying radius of mosquitoes.
Tom Skinner, spokesman for the Centers for Disease Control and Prevention, said evidence is mounting to suggest local transmission via mosquitoes is happening in South Florida.