Health officials in Florida reported 10 more Zika virus cases, increasing the number of infected people in the sunshine state to 14.
The earlier recorded Zika infections were contracted by travelers coming from abroad, but the new cases are among the first spread through local mosquitoes.
Florida Department of Health conducted a community door-to-door survey in three locations around Miami, which led to the identification of the new cases. However, all of the virus infections were confirmed from only one location.
"Based on the DOH's investigations, two locations have been ruled out for possible local transmissions of the Zika virus. DOH believes local transmissions are still only occurring in the same square mile area of Miami," Florida Governor Rick Scott said.
Center for Disease Control and Prevention (CDC) issued a warning to pregnant women to not visit northern part of Miami where most of the cases were found.
The warning was applicable to Wynwood, the one-mile area north of central Miami. Women who are pregnant and live in or visited the area since June 15 were advised to consult with their doctor.
CDC director Tom Frieden said that measures to inhibit mosquito growth in the area were not entirely successful.
"We also don't yet have ideal ways to control the particular mosquitoes that spread Zika, and we need better methods and tools for mosquito control," Frieden said. "In Miami, aggressive mosquito control measures don't seem to be working as well as we would have liked."
"Nothing that we have seen indicates widespread transmission but it is certainly possible there could be sustained transmission in small areas," he added.
Zika virus is transmitted by vector Aedes aegypti, and through blood transfusions, sexual contact, and from mother to baby.
Scientists have linked the virus to microcephaly and other anomalies in babies.
A majority of people infected with Zika virus do not show any symptoms or are asymptomatic, but others develop rash, fever, body aches, and redness of eyes, which usually appear about three to seven days after the mosquito bite. The symptoms may last up to weeks, and its treatment is mainly with recommended rest and antipyretics and analgesics.
More than 1,600 positive Zika infections were previously recorded in the US, including about 100 in California, but they were associated with foreign travel. The virus continues to spread in Central and South America, including parts of Mexico, Ecuador, Dominican Republic, and Brazil.
