As the Zika epidemic has spread like wildfire throughout South and Central America, the United States has largely been spared … but Southern states like Louisiana are starting to see some concerning signs. It was Florida that announced the first local transmission from an infected mosquito late last month, but it’s popping up elsewhere as well, with the Louisiana Department of Health just confirming four new cases of Zika virus and 19 total state residents who have the infection.

As is typically the case, the patients had travelled to Zika-prone areas of the Americas and had sought medical care in Louisiana after getting back. All 19 cases are travel-associated, but as the Florida case shows, it may be only a matter of time before someone contracts Zika locally.

Local transmission happens when an infected mosquito in the area bites a person, transmitting the virus.

Public health officials in Louisiana are scrambling to get ahead of the problem. They know that early detection of the virus is key to preventing it from spreading like wildfire.

You can avoid Zika by avoiding mosquito bites. That means wearing insect repellent, wearing long sleeves and pants that are light colored, sleeping underneath a mosquito net if you’re outdoors, and getting rid of any nearby stagnant water.

“Our surveillance activities include working with hospitals and other health care providers who notify us if and when a possible Zika case is diagnosed,” Dr. Frank Welch, Medical Director for the department’s Bureau of Community Preparedness, said in the statement. “We also work with mosquito control agencies throughout the state who conduct mosquito testing in areas of known human cases to determine if mosquitos in those areas are carrying the virus.”