How Health Experts Investigate Possible Zika Outbreaks

— -- The Florida Health Department is now investigating four Zika infections that may have been transmitted locally. More than 1,300 people have been diagnosed with Zika in the U.S. and virtually all contracted the disease while traveling abroad. A small number were due to sexual transmission of the disease.

If the investigation determines that Zika was passed on by an infected mosquito in Florida, it would be the first occurrence of a local transmission in the continental United States. Concern over a possible Zika outbreak has led the U.S. Centers for Disease Control and Prevention to offer assistance to the Florida Health Department.

After two new cases were reported, the Florida Health Department expanded its investigation and started going door-to-door to reach people in areas where the infections were reported. Sample collections, including urine samples, are being requested to determine if there are ongoing infections, according to the Florida health officials.

Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical School, explained to ABC News that an epidemiological investigation to determine if there is an outbreak can take time as many investigators fan out over neighborhoods to look for any sign of the virus in both insects and people.

Investigators will "try to figure out where the infection was likely acquired," said Schaffner. If they believe it was locally acquired, they'll start searching in different areas for the Aedes Aegypti mosquito that has been linked to the disease.

He also explained that urine tests are used to help identify a potential outbreak because they are easy to acquire and don't require medical staff as blood samples do.

"It can be very elaborate" to do these investigations, Schaffner explained. "As we talk about this, all of these investigations are very personnel dependent."

Should an outbreak of the virus be confirmed in Florida, Schaffner said the health department would likely send out mosquito control experts to spray affected homes with insecticides.

"They will actually have people going through backyards and looking at sites where they need to spray," he said.