The CDC advised people returning from the affected area of Florida to use mosquito repellent for three weeks to protect their families and guard against further transmission at home.

It also recommended that women avoid getting pregnant for up to eight weeks after returning from the affected area.

The agency said that pregnant women who live in or traveled to the affected area after June 15 should be tested for Zika.

Florida health officials initially tested individuals in three locations in Miami-Dade and Broward counties, but ruled out two of those locations. Six of the 10 new cases are asymptomatic and were identified through a door-to-door campaign, which involved the collection of urine samples.

Infectious disease experts expressed doubt that the outbreak was contained to such a small area of Miami.

"To assume that it's just restricted to these few square blocks is presumptuous," said Dr. Peter Hotez, dean for the National School of Tropical Medicine at Baylor College of Medicine in Houston.

Hotez believes there are other likely local outbreaks occurring and that more can be expected in the next six weeks in Florida and other Gulf Coast states where the mosquito that carries the virus is common.