An unseen danger lurks beneath the surface of the waters of the Chesapeake Bay, as one man found out recently. Rodney Donald, 66, a resident of Maryland, scraped his leg while crabbing, swimming, and kayaking in the bay earlier in the month. His scrape became infected with a bacteria species called Vibrio vulnificus, which feeds on flesh and can be deadly if not treated.

Donald was hospitalized at MedStar Washington Hospital Center in Washington, D.C., on Jul. 11, with severe swelling in his right leg. Hospital doctors ended up performing six separate surgeries, including a skin graft, over the subsequent two weeks. Donald was finally released last Thursday.

Eating contaminated seafood or exposing an open wound to warm seawater can cause a vibrio infection, according to the U.S. Centers for Disease Control and Prevention (CDC). Symptoms include fever, chills, vomiting, diarrhea, abdominal pain, septic shock, and visible lesions or sores.

This particular bacterium thrives in brackish water, areas where fresh and salt water meet and mix. It prefers warmer water and grows best between May and October. Last year, the Maryland Department of Health and Mental Hygiene reported a ten-year high number of cases with the total reaching 57. The region overall is observing a rising number of cases.

The Chesapeake Bay Foundation found in 2009 that the increase in infections is linked to pollution and unusually warm summer temperatures in previous years.

Last year, the number of cases of vibrio infection in Maryland was 14. This year, six cases have been reported to date. Across the country, roughly 95 cases occur annually, including 85 hospitalizations and 35 deaths, according to the CDC.