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Vibrio vulnificus is scarcely recognized by many microbiologists, less so by the public. Yet, in this country, the bacterium causes a disease with over a 50 percent mortality rate, and it causes 95 percent of all seafood-related deaths.

Vibrio vulnificus is a Gram-negative, motile curved bacterium found in marine and estuarine environments. It has been isolated from seawater, sediments, plankton and shellfish (oysters, clams and crabs) located in the Gulf of Mexico, the Atlantic Coast as far north as Cape Cod, and the entire U.S. West Coast. The bacterium thrives in warm seawater and is part of a group of vibrios that are "moderate halophiles", meaning they require salt for growth. Vibrios are frequently isolated from oysters and other shellfish in warm coastal waters during the summer months. This correlates with the peak incidence of disease caused by the bacterium.

Vibrio vulnificus is a Gamma Proteobacterium in the Family Vibrionaceae, with two other human pathogens Vibrio cholerae, the agent of epidemic cholera, and Vibrio parahaemolyticus, which causes acute diarrhea. Vibrios are one of the most common organisms in surface waters of the world. They occur in both marine and freshwater habitats and in associations with aquatic animals. Some species are bioluminescent and live in mutualistic associations with fish and other marine life. Other species are pathogenic for fish, eels, and frogs, as well as other vertebrates and invertebrates.

V. cholerae and V. parahaemolyticus are pathogens of humans. Both produce diarrhea, but in ways that are entirely different. V. parahaemolyticus is an invasive organism affecting primarily the colon; V. cholerae is noninvasive, affecting the small intestine through secretion of an enterotoxin.

Vibrio vulnificus is an emerging pathogen of humans. It causes wound infections, gastroenteritis, or a syndrome known as primary septicemia. It was first recognized as an agent of disease in 1976.  The first documented case of disease caused by the bacterium was in 1979.

Figure 1. Vibrio vulnificus is a typical marine vibrio - a slightly curved bacterium, motile by means of a single polar flagellum.

Disease

V. vulnificus causes disease in individuals who eat contaminated seafood (usually raw or undercooked oysters) or have an open wound that is exposed to seawater. Among healthy people, ingestion of V. vulnificus can cause vomiting, diarrhea, and abdominal pain.  Most V. vulnificus infections are acute and have no long-term consequences.

In immunocompromised persons, particularly those with chronic liver disease, V. vulnificus can invade the bloodstream from either a wound or from the GI tract, causing a severe and life-threatening illness called primary septicemia, characterized by fever, chills, septic shock and death. Blistering skin lesions accompany the disease in about 70% of the cases. V. vulnificus bloodstream infections are fatal about 50% of the time.

Although V. vulnificus is a rare cause of disease,  it is likely that it is unrecognized and underreported (one estimate of the total number of cases annually in the U.S. is as high as 45,000). Between 1988 and 1995, CDC received reports of over 300 V. vulnificus infections from the Gulf Coast states, where the majority of cases occur.

Persons who are immunocompromised, especially those with chronic liver disease, are at risk for V. vulnificus when they eat raw seafood, particularly oysters.  These individuals are 80-200 times more likely to develop V. vulnificus primary septicemia than are healthy people. For this particular risk group, the infection carries one of the highest mortality rates of all bacterial infections.

Health conditions that place a person at risk for serious illness or death from V. vulnificus infection include liver disease, hemochromatosis, diabetes, stomach problems, kidney disease, cancer, immune disorders (including HIV) and long-term steroid use. In these individuals, the bacterium enters the blood stream, resulting in septic shock, rapidly followed by death in many cases. Such individuals are strongly advised not to consume raw or inadequately cooked seafood.