US health officials warned pregnant women to avoid traveling to a neighborhood in Miami on Monday after Florida said it had 10 more cases of Zika caused by the bite of local mosquitoes, bringing the total to 14.
At the request of Gov. Rick Scott, the U.S. Centers for Disease Control and Prevention is sending in a special emergency response team of eight disease experts to assist Florida in its investigation.
The state has been handling the investigation largely on its own since early July, when the first case of a possible Zika infection caused by local mosquitoes was suspected.
CDC Director Dr. Thomas Frieden said in a conference call that local mosquito control efforts have not worked as well as hoped, but so far, the outbreak does not appear to have traveled very far.
"Nothing we have seen suggests widespread Zika virus transmission," Frieden said.
The ongoing Zika outbreak was first detected last year in Brazil, where it has been linked to more than 1,700 cases of the birth defect microcephaly. Since that time the virus has spread rapidly through the Americas.
On Friday, Florida said the first four cases of Zika in the state likely were caused by mosquitoes, the first sign that the virus is circulating locally, although it has yet to identify mosquitoes carrying the disease.
The 10 new cases announced on Monday bring the total to 14. Of these, 12 are men and 2 are women.
Dr. William Schaffner, an infectious disease expert at Vanderbilt University School of Medicine, said there is concern that people infected in Florida will travel to other areas of the country where Zika could then be spread through local mosquitoes there.
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.
A map of the neighborhood can be found here:
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.
Florida said it began investigating a possible case of local Zika transmission on July 7. But the CDC was first informed of the case on July 18, a day before the state announced it had a possible case of non-travel related Zika, according to CDC spokeswoman Kathy Harben.
CDC has been coordinating with Florida officials and sent Dr. Marc Fischer, a CDC epidemiologist, on July 22 at the state's request.
Reuters was first to report that as of last Friday, Florida still had not activated a CDC Emergency Response Team (CERT) to help with its investigation, raising concerns from infectious disease experts that the state was not taking every step it could to contain the spread of Zika in the continental United States.
Frieden said in a conference call there were signs of possible local transmission as early as mid-June.
He said a full emergency response team - which include experts in epidemiology, vector control and logistics - will be on the ground in Florida on Tuesday.
White House spokesman Eric Shultz told reporters that Florida will be redoubling its vector control efforts in the outbreak area, which involves a 1-square-mile (2.6 square km) area in the mixed-use area north of downtown Miami. CDC said pregnant women who live or work in the area and their partners should make every effort to avoid mosquito bites.
Schaffner and Hotez said the government must come up with proper funding to fight Zika. "Local and state health department budgets are very tight," Schaffner said.
President Barack Obama asked Congress for $1.9 billion to fund a Zika response last spring, but arguments over funding levels resulted in a stalemate, and Congress adjourned for the summer without authorizing any funding.