On Aug. 13, the Massachusetts Department of Public Health issued a warning regarding a potentially dangerous bacterium found in the waters of Cape Cod: Vibrio vulnificus.
This warning was prompted by an “extremely rare case” of Vibrio vulnificus infection that occurred in an individual after swimming with an open wound at Old Silver Beach in Falmouth, Mass. Since the announcement, no new cases have been identified, though the warning still stands.
The genus Vibrio encompasses many species of bacteria that can cause an infection called vibriosis. In 2025, Massachusetts reported 71 cases of vibriosis, with 30% involving hospitalization. Species of Vibrio that can cause illnesses include Vibrio fluvialis, Vibrio parahaemolyticus and Vibrio vulnificus.
Vibrio species are often found in saltwater and brackish water (a mixture of saltwater and freshwater). These bacteria thrive in higher temperatures, especially during the summer months when coastal waters are warmer. The Centers for Disease Control and Prevention reports that it is contracted through the consumption of “raw or undercooked shellfish, particularly oysters” and through an open wound in coastal waters. Regardless of the mechanism of infection, the symptoms usually begin less than 24 hours after contact. Symptoms from ingestion include nausea, vomiting, chills and diarrhea. Symptoms of infection from a wound include swelling, redness, fever and blisters.
According to the University of Florida, Vibrio vulnificus is considered the “most dangerous” species of Vibrio. According to the CDC, about one in five individuals with Vibrio vulnificus infection die within 48 hours of contact. In wounds, it can cause necrotizing fasciitis, which refers to death in the flesh around open wounds. In fact, the general public often refers to Vibrio vulnificus as a ‘flesh-eating bacterium’ due to this. Furthermore, Vibrio vulnificus can cause thrombocytopenia, sepsis, internal bleeding and damage to the organs.
Some individuals are at a heightened risk for Vibrio infection. The Cleveland Clinic reports that individuals with liver disease, hemochromatosis, kidney failure, diabetes and those who are immunocompromised are at a higher risk.
When detected early, Vibrio vulnificus can be cured with antibiotics, including doxycycline, ceftazidime and ciprofloxacin. However, in more severe cases, hospitalization and procedures including wound debridement, blister draining and limb amputation can be necessary.
The CDC guidelines for avoiding vibriosis include not eating raw or undercooked seafood (particularly oysters), washing hands after handling raw shellfish, avoiding coastal water if you have an open wound (even if small) and covering wounds that could potentially come in contact with coastal water.
