This is important for one simple reason: It means more Zika cases are likely to pop up in the South soon.
Zika was first confirmed in Florida's Miami-Dade County on July 29, when a pregnant woman tested positive for the mosquito-borne and sexually transmitted virus. Unlike all of the other Zika cases reported in the US at the time, she had no travel history to a country with Zika.
Mosquitoes have since infected a small number of people in the area. As of August 22, there were 37 locally-acquired cases in Florida, mostly concentrated in a one square mile area of Miami's Wynwood neighborhood.
But now mosquitoes are transmitting Zika in a broader area of Miami — specifically the tourist-heavy Miami Beach area, which is outside the one square mile in Wynwood. On August 23, health officials also confirmed a non-travel Zika case on the other side of Florida, in Pinellas County.
These new cases have come with an expanded travel advisory from the CDC. The has advised pregnant women to stay out of the area of Miami Beach where Zika is spreading, and suggested pregnant couples consider avoiding nonessential travel to Miami-Dade. These travel warnings will likely expand as more cases pop up, jeopardizing local business and tourism.
A small Zika outbreak in Florida isn't surprising. Zika has been identified in mosquitoes in more than 60 countries and territories over the past year, and the CDC has warned that the southeastern part of the US — particularly Florida and Texas — was at risk of outbreaks during mosquito season this year. It's the region where the Zika-carrying Aedes aegypti mosquitoes thrive in the greatest concentrations.
But don't panic: Zika is not expected to spread far in the continental US the way it has in Latin America and the Caribbean.
Based on data from similar viruses like dengue and chikungunya, also carried by Aedes aegypti mosquitoes, officials expect small and limited outbreaks here.
The main reasons: the climate and socioeconomics of the US.
You won't find the Aedes aegypti mosquito in most of the US because the mosquito can't survive in cooler climates. The Southern areas that are hospitable to Aedes already have mosquito control efforts in place to deal with other, better-known mosquito-borne viruses. Americans are also likelier to have housing with air conditioning and screens. All these factors reduce the risk of Zika spread.
Zika isn't a big health threat for most people
For most people, Zika virus isn't a big health threat. In 80 percent of those infected, it causes no symptoms at all.
Twenty percent of people with the virus will experience relatively minor symptoms including fever, aches, headache, and rash. They usually appear two to 12 days after a bite and go away within a week.
For babies, however, the health effects can be devastating. The virus can move through the placental barrier and attack fetuses, causing birth defects, including microcephaly, or even fetal death.
Health officials are still learning about all the ways Zika can spread, but they believe mosquitoes are the main carriers and recommend taking precautions to avoid bites. Since Zika can be sexually transmitted, they also suggest people practice safe sex with condoms or even abstain from sex, particularly if one's partner is pregnant, and recommend specific precautions for those thinking of becoming pregnant soon.