An outbreak of a flesh-eating bacteria along Texas’ Gulf Coast has infected nearly a dozen people, authorities warned.

Officials in Galveston County said 11 cases of vibrio infections have been reported so far this summer, compared to only two at this time last year, according to a report by Houston-area news outlet KHOU Channel 11. Of those infected, eight were from out of town.

Vibrio bacteria occur naturally in coastal waters, including salt water and brackish water, a mixture of salt and fresh water. It is found in higher concentrations in the summer when water temperatures are warmer.

Vibrio can cause two kinds of illnesses. The more common is caused by eating raw or undercooked shellfish, particularly oysters. Symptoms include abdominal cramps, diarrhea, nausea, vomiting and dehydration.

The other, potentially more serious infection occurs when an open wound comes into contact with coastal waters. Most of the cases in Galveston were the result of contact with water, a spokesperson for the Galveston County Health Department said in an email Friday.

Symptoms can include fever and redness, pain, swelling, warmth, discoloration and discharge of fluid around the wound, according to the U.S. Centers for Disease Control and Prevention.

In the worst cases, the bacteria can lead to necrotizing fasciitis, a severe infection in which the flesh around an open wound dies, which is why vibrio is frequently called a “flesh-eating bacteria.” Such severe infections are rare and tend to occur in people with pre-existing conditions that cause weakened immune systems, health authorities say.

The conditions of those infected are not known. Galveston officials said in the release they are working to identify the source of the infections and implement measures to prevent additional cases.

“There’s no need to panic,” Dr. Phillip Keiser, CEO of the Galveston County Health District, said in a statement. “Use common sense: avoid raw seafood, practice good hygiene, and stay informed to keep safe.”

People who experience severe gastrointestinal issues or wound infections following exposure to seawater should seek prompt medical attention, as early diagnosis and treatment are crucial to managing symptoms and preventing complications, the county said.