United States health officials are warning of a deadly flesh-eating bacteria that’s been infecting humans this summer. The bacteria thrive in warm seawater, and the media is fear-mongering, saying this is a chilling reminder of the potential danger associated with vacation pastimes like swimming and wading.

Infections are caused by the bacteria Vibrio vulnificus and have a 20% fatality rate according to the Centers for Disease Control and Prevention. That makes early and appropriate treatment crucially important, says Northeastern University professor Brandon Dionne, a clinical pharmacist in infectious diseases. “It’s pretty rare when it happens, but it can be very severe,” Dionne says. “The bacteria are not actually eating the flesh, but the toxins they make break down tissues and cause a lot of tissue damage and destruction,” he added.

Salty or brackish water of the type found in estuaries can harbor Vibrio vulnificus, which can enter the body through open wounds or cuts, says Dionne, who is also an associate clinical professor of pharmacy and health systems sciences.

According to a report by Medical Xpress, dozens of cases have been reported this year across the South and Gulf states, and at least 10 people have died. Still, one of the most recent cases occurred on Cape Cod in Massachusetts, where a man contracted the infection after going into the water on Old Silver Beach in Falmouth.

“It can spread very quickly and progress quickly,” Dionne warns.  “If you get it in your foot from a cut or something, it can spread all the way up your leg and into the trunk of your body. That tissue damage can happen very rapidly. It can put the body into shock and ultimately lead to mortality,” Dionne says.

He says the toxins released by the bacteria cause a degradation of the tissues and destroy skin cells and the fascia layer between skin and muscle, which is why the infection is also known as necrotizing fasciitis. The bacteria are not literally eating human flesh during an infection.

In most cases, antibiotics will help treat the infection. “Treatment is very case by case, but patients will often be on antibiotics for a few weeks while they are trying to heal,” Dionne adds.