ATLANTA, Ga. (WPVI) --Florida health officials have found another 10 people infected with Zika virus, likely from mosquitoes.
In light of that, the CDC today urged pregnant women to stay away from the area in South Florida affected by the virus.
And the advisory stretches back to June 15th.
If you're pregnant and were in this area anytime after June 15th, you should let you doctor know.
Anyone who was there during that time should use insect repellent for three weeks after you return.
Find the complete travel advisory here.
The 10 new cases, along with 4 cases announced Friday, raise the number of locally-transmitted Zika cases to 14.
The CDC is sending an emergency response team to the affected square-mile sized area just north of downtown Miami.
The main focus will be to protect pregnant women and stop the spread of Zika.
Women living there should prevent mosquito bites and protect themselves against sexual transmission.
Governor Rick Scott has asked the CDC to activate its Emergency Response Team, which is underway.
Team members will help the state investigate cases, control mosquitoes and monitor for birth defects linked to the virus.
The rise in cases means some mosquitoes in the state are carrying and spreading the virus, although CDC Director Dr. Tom Frieden said again today that none of the thousands of mosquitoes tested in Florida in recent months has carried Zika virus.
"Once something starts, we nip it in the bud," says Dr. Aileen Marty, an infectious disease professor.
Mosquito control is out spraying, but the CDC admits battling the Aedes Aegypti mosquito is tough.
"In Miami, aggressive mosquito control methods don't seem to be working as well as we would like," said Dr. Frieden during today's telebriefing.
Dr. Frieden says that despite days of intense spraying, numbers of this species found in traps or standing water hasn't dropped as much as it would with other mosquito species.
He said there could be several explanations: 1.)They have become resistant to insecticides; 2.)They could be hiding in undiscovered breeding areas: 3.)This mosquito operates differently.
CDC officials said they could not remember another time in the 70-year history of the disease-fighting agency when it told members of the public not to travel someplace in the U.S.
The virus can linger in the blood and urine for weeks, and has been found in sperm for months.
As a result, the CDC said men and women who have recently been in the affected area should wait at least eight weeks before trying to conceive a child.
Dr. Frieden says pregnant women must take the advisory seriously.
"What we don't know about Zika virus is even more unsettling. We don't know the long-term impact of Zika to infected mothers who don't have known signs of microcephaly," said Dr. Frieden.
"These effects may become known only months or years later."
The travel warning covers an area of about one square mile in Wynwood to the east of Interstate 95 and south of I-195.
It's large enough, health officials said, to provide a buffer around the suspected hot zone. The tropical mosquito that spreads Zika travels less than 200 yards in its lifetime.
Some experts said that's far too small a radius.
Dr. Peter Hotez, a tropical medicine expert at the Baylor College of Medicine in Texas, said the CDC should be more cautious and expand the travel advisory to all of Miami-Dade County.
Workers have already been going door to door to test more people.
80-percent won't have symptoms but if they have the virus and are bitten again by a mosquito, it could spread to the bug's next victim.
Dr. Pablo Tebas at Penn Medicine says it's possible we'll see local cases, but it depends on how quickly the virus spreads and how far North it will travel.
He's part of a team that's launched the first human trial of a Zika Virus *vaccine. He's optimistic but time is of the essence.
"I hope we win the race, get the vaccine before Zika gets to us," says Dr. Tebas.