A swimmer at a Cape Cod beach has been infected with an extremely rare bacteria, according to officials who are alerting the public about the potentially life-threatening illness.

The state Department of Public Health is warning residents and visitors to the potential danger of Vibrio bacteria in coastal waters after the rare case was confirmed in an older person who was swimming with an exposed wound at Falmouth’s Old Silver Beach in Buzzards Bay.

There have been seven confirmed Vibrio vulnificus cases among Massachusetts residents in the last several years, including four who were likely exposed in Massachusetts.

The infections are more common in the warm waters of the Gulf Coast, and Louisiana and Florida have reported unusually large numbers of cases this year.

“Vibrio bacteria normally live in warm, salt or brackish waters along the Atlantic coast,” Public Health Commissioner Robbie Goldstein said in a statement. “Heat waves and above-average water surface temperatures create favorable conditions for Vibrio bacteria to grow, making May through October generally the peak season for these bacteria.

“People with open wounds who spend time in the water, or those who consume contaminated shellfish, can develop an infection when the bacteria enter the body,” he added. “Sometimes these infections can spread through the bloodstream and cause severe, even life-threatening illness.”

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In Massachusetts between 2015 and 2024, there were an average of 88 cases of Vibrio infection per year. Most of these infections were the result of people consuming shellfish contaminated with the bacteria.

Among the various Vibrio bacteria species, 71 confirmed and probable Vibrio cases have been reported among Massachusetts residents so far in 2025. Thirty percent have reported hospitalization, and there have been no verified Vibrio-related deaths.

Anyone exposed to the bacteria can get a Vibrio infection. Individuals with liver disease, cancer, diabetes, HIV, or thalassemia, and those receiving immunosuppressive therapy for the treatment of disease are at greater risk for severe disease from Vibrio following exposure.

To prevent Vibrio wound infections:

— If you have an open wound (including from a recent surgery, piercing, or tattoo), cut, or scrape: Cover your wound with a waterproof bandage or stay out of coastal waters when engaging in activities such as wading, swimming, and fishing.

— Wounds should also be covered when handling raw seafood, its drippings, or its juices.

— Immediately wash wounds and cuts thoroughly with soap and clean running water after contact with coastal waters.

— If you are at increased risk for infection, wear clothes and shoes that protect you from cuts and scrapes when in coastal waters.

— People with wounds, whether covered or not, should avoid handling raw seafood, its drippings, or its juices.

People who have an open wound that has been exposed to warm, coastal waters are advised to monitor for signs and symptoms of infection for seven days, and are advised to seek medical attention if they develop fever, chills, dangerously low blood pressure, blistering skin lesions or any redness, pain, swelling, warmth, discoloration, or discharge at the site of the wound.