Louisiana has confirmed nine cases of Vibrio vulnificus infections this year, the state’s health department said last week in a news release. All were hospitalized, and five died. During the same period over the previous decade, Louisiana reported an average of seven cases and one death.

“Seek medical care immediately if a wound exposed to brackish or salt water becomes red, swollen, painful, warm or discolored,” officials said in the release. “Tell the health care provider about the water exposure.”

The Gulf is an ideal environment

Vibrio bacteria thrive in seawater and in the brackish mix of fresh and saltwater found in estuaries and lagoons. Most infections are reported from May to October, and most happen in states along the Gulf Coast. Doctors say the Gulf is an ideal environment with the right amounts of salt and heat to let this organism proliferate.

The mostly deadly type is Vibrio vulnificus, according to the Centers for Disease Control and Prevention. As many as one in five of those infections are fatal, a much higher rate than other types of Vibrio bacteria.

Florida, which tends to have more infections than other states, has reported 14 Vibrio vulnificus cases and two deaths so far this year, compared with 33 cases and five deaths for all of last year. Records show more cases in years when Florida is hit by tropical storms and hurricanes.

Bacteria enters through breaks in the skin

Some people become infected by eating raw or undercooked shellfish — particularly oysters. But a large percentage fall ill when the person is in ocean or brackish water and the bacteria enter the body through small breaks in the skin.

Doctors say severe cases are seen more often in elderly patients, people with weakened immune systems, and those with liver disease, diabetes and certain chronic illnesses.

Scientists say climate change is helping the germs proliferate and spread northward. A 2023 study found that the northernmost case has been shifting by about 30 miles each year, and that cases overall have been rising.

Beachgoers can protect themselves

Vibrio vulnificus can enter the body through unhealed cuts and scrapes, recent piercings and tattoos, and recent surgical incisions. People should immediately wash cuts and scrapes thoroughly with soap and clean running water after coming in contact with coastal waters or raw seafood, the CDC said. They should see a doctor if they start to develop symptoms such as fever, chills, and hot red areas on the skin that start to turn dark and blister.

Oysters are a particular risk, and there is no way to tell if an oyster is contaminated just by looking at it. People should wash hands with soap and water after handing raw shellfish and wear protective gloves if they have a weakened immune system and are at a higher risk of infection.

Health officials also offer cooking instructions for clams, mussels and other shellfish. They recommend throwing away any with open shells before boiling or steaming.