FRIDAY, July 29, 2016 (HealthDay News) -- The United States is apparently experiencing its first local outbreak of the Zika virus, with four human infections reported in South Florida very likely caused by mosquito bites, the federal Centers for Disease Control and Prevention announced Friday.
"All the evidence we have seen indicates that this is mosquito-borne transmission that occurred several weeks ago in several blocks in Miami," said CDC Director Dr. Tom Frieden. "We continue to recommend that everyone in areas where Aedes aegypti mosquitoes are present -- and especially pregnant women -- take steps to avoid mosquito bites. We will continue to support Florida's efforts to investigate and respond to Zika and will reassess the situation and our recommendations on a daily basis."
The CDC has sent a medical epidemiologist to assist Florida officials in their ongoing investigation of the outbreak, the agency said.
Zika infection poses significant risks to pregnant women, because it can cause the birth defect called microcephaly, which results in babies born with undersized heads and underdeveloped brains.
But, the virus poses little threat to most other people, with about 80 percent of those infected never noticing any symptoms.
The four cases are in the South Florida counties of Miami-Dade and Broward.
CDC officials have said repeatedly they expect to see cases of local transmission of the Zika virus this summer in warm, humid southern states such as Florida, Louisiana and Texas. The virus is typically transmitted through the bite of Aedes mosquitoes.
Responding to the reports earlier this week of possible local transmission of the Zika virus in South Florida, the U.S. Food and Drug Administration said Thursday that it was asking all blood establishments in Miami-Dade and Broward counties to stop collecting blood immediately. They can resume collections once the blood centers put in place testing for each unit of blood collected. The centers can use an available "donor screening test for Zika virus RNA" or an "approved or investigational pathogen inactivation technology," the agency said in a news release.
The FDA urged nearby counties to take similar precautions to safeguard blood supplies.
As of July 27, 1,658 cases of Zika had been reported to the CDC in the continental United States and Hawaii; none of those cases were the result of local spread by mosquitoes. These cases included 15 believed to be the result of sexual transmission and one that was the result of a laboratory exposure, the CDC said. Virtually all of the Zika infections reported in the United States had been linked to travel to countries with Zika outbreaks in Latin America or the Caribbean. Brazil has been the epicenter of the Zika epidemic to this point.
In addition to mosquitoes, the Zika virus can be transmitted through sex. The CDC has reported 15 cases of sexually transmitted infections. These infections are thought to have occurred because the patients' partners had traveled to countries where Zika is circulating, the CDC said.
The Zika virus also has been linked to a rare paralyzing condition called Guillain-Barre syndrome.
The CDC advises pregnant women not to travel to an area where Zika transmission is ongoing, and to use insect repellent and wear long pants and long-sleeved shirts if they are in those areas. Partners of pregnant women are advised to use a condom to guard against sexual transmission during pregnancy.
The U.S. Centers for Disease Control and Prevention provides more information on mosquito-borne diseases.
This Q&A will tell you what you need to know about Zika.
To see the CDC list of sites where Zika virus is active and may pose a threat to pregnant women, click here.