Four cases of the Zika virus in Florida are being investigated by health officials as it appears that they are not related to travel. The virus has mostly been known to have spread by travel to a region where Zika is more prevalent and in some cases through sexual transmission.

The new cases, which were detected in the Miami-Dade and Broward counties in the United States, have raised concerns that mosquitoes in the country have begun to carry the virus, BBC reported. Zika, which was previously only known to cause moderate cold and flu-like symptoms, is now causing multiple neurological disorders, as well as microcephaly in babies. Microcephaly is a condition that causes babies to be born with abnormally small heads.

Florida officials said Wednesday that they are yet to draw any conclusion from their investigation but are trying to determine how it was transmitted.

According to reports, the confirmation on whether Zika is being carried by mosquitoes locally will be made after scientists survey houses and people within a 150-meter radius of the cases.

Earlier this month, health officials said that a Utah man who died after contracting the Zika virus may have passed it on to his caregiver, making it the first case in the U.S. where a person was infected without having sexual contact or visiting an affected area.

“The new case in Utah is a surprise, showing that we still have more to learn about Zika,” Centers for Disease Control and Prevention medical epidemiologist Erin Staples said at the time.

The World Health Organization declared the Zika outbreak, which has spread across Latin America and in Caribbean nations, an international health emergency on Feb. 1.