Health officials in Louisiana are urging beachgoers to exercise caution amid a summertime surge in infections caused by Vibrio vulnificus, a bacterium commonly found in warm coastal waters.

Louisiana has confirmed nine cases of Vibrio vulnificus infection so far this year, according to a news release issued last week by the state's health department. All nine patients required hospitalization, and five died. Over the same period during the previous decade, Louisiana averaged seven cases and one death annually.

"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."

Vibrio bacteria flourish in seawater and in the brackish mixture of fresh and saltwater typical of estuaries and lagoons. The majority of infections are reported between May and October, with most occurring in states along the Gulf Coast. Physicians note that the Gulf of Mexico provides an ideal habitat, offering the precise combination of salinity and warmth that allows the organism to thrive.

According to the Centers for Disease Control and Prevention, Vibrio vulnificus is the most deadly type of Vibrio bacteria. As many as one in five of these infections prove fatal — a significantly higher mortality rate than other Vibrio species. When the bacteria invade the bloodstream through a wound, they can cause necrotizing fasciitis, a rapidly spreading infection that destroys skin and soft tissue, which is why V. vulnificus is sometimes called a "flesh-eating" bacterium.

Florida, which typically reports more infections than any other state, has documented 14 Vibrio vulnificus cases and two deaths so far this year, according to state health data. That compares with 33 cases and five deaths for all of last year. Historical records indicate that case counts tend to rise in years when Florida is struck by tropical storms and hurricanes, when storm surges and floodwaters expose more residents to contaminated water.

Some individuals contract the infection by consuming raw or undercooked shellfish, particularly oysters. However, a substantial proportion of cases occur when people are exposed to ocean or brackish water and the bacteria enter the body through minor breaks in the skin.

Physicians report that severe cases are more frequently observed among elderly patients, individuals with weakened immune systems, and those living with liver disease, diabetes, or certain other chronic conditions. Treatment typically involves intravenous antibiotics, and in advanced wound infections, surgical removal of damaged tissue may be necessary to halt the spread.

Scientists say climate change is contributing to the proliferation and northward spread of the pathogen. A 2023 study published in Nature found that the northernmost documented case has been shifting approximately 30 miles poleward each year, and that overall case counts have been climbing. Researchers linked the trend to rising coastal water temperatures, which have expanded the seasonal window and geographic range in which the bacteria can reproduce.

Vibrio vulnificus can enter the body through unhealed cuts and scrapes, recent piercings or tattoos, and recent surgical incisions. The CDC advises people to wash cuts and scrapes immediately and thoroughly with soap and clean running water after any contact with coastal waters or raw seafood. Individuals should seek medical attention if they develop symptoms such as fever, chills, or hot, red areas on the skin that begin to darken and blister.

Oysters present a particular risk, and there is no visual method for determining whether an oyster is contaminated. Health authorities recommend washing hands with soap and water after handling raw shellfish and wearing protective gloves for those with weakened immune systems or otherwise elevated infection risk.

Health officials also provide cooking guidance for clams, mussels, and other shellfish: any specimens with open shells should be discarded before boiling or steaming.

This story was originally featured on Fortune.com.