Raw Fish Bacteria

By Peter Galvin, MD

It has long been known that eating raw fish, especially raw shellfish, is never a good idea (with apologies to sushi aficionados). The reason is because of the potential infectious diseases that may be transmitted by raw shellfish. Raw shellfish has been known to carry viruses like hepatitis. Another infectious agent is carried by raw fish is known by the genus Vibrio, of which there are three types that can infect humans – Vibrio cholerae, parahaemolyticus, and vulnificus. All three bacteria can cause severe watery diarrhea and fever, V cholerae being the causative agent of cholera. Typically, bacteria of the Vibrio genus live in salt water and cannot tolerate fresh water, however V vulnificus is usually found in brackish water (a mix of salt and fresh water, i.e., the Hudson becomes brackish a few miles north of the Tappan Zee bridge). About 100 cases per year of V vulnificus are reported in the U.S., however people with mild disease are usually not tested, so the actual number of cases is unknown. New Orleans saw a large outbreak of V vulnificus following Hurricane Katrina. In the U.S., the mortality rate associated with V vulnificus is approximately 33%, and it causes about 95% of seafood-related deaths.

V vulnificus can cause both diarrheal illness and wound infections (if broken skin is exposed to contaminated water or seafood). It is found in warm coastal regions around the world. It is rarely detected in water colder than 13 degrees Celsius (55.4 degrees F), so most U.S. infections occur between the months of May and October. Hurricanes, storm surges, and coastal flooding are associated with an increase in V vulnificus infections. People become infected by eating raw or undercooked seafood (primarily oysters, less commonly other shellfish or other fish) or by having an open wound that is exposed to seawater or contaminated seafood products. Typical symptoms include diarrhea for several days, nausea, vomiting, stomach cramping, fever, and chills. Those with severe infections (typically people with compromised immune systems) may develop a bloodstream infection (sepsis), which may be life-threatening. V vulnificus wound infections may cause skin redness, warmth, swelling, and pain (cellulitis) in an affected area. A severe skin infection may cause muscle and wide-spread tissue destruction.

Those most at risk for severe V vulnificus infections include those with liver disease (i.e., cirrhosis), cancer, HIV, diabetes, or certain blood disorders (thalassemia). Also, at risk are those who take immunosuppressants or medications to decrease stomach acid. Diagnosis is made by detecting V vulnificus in blood, stool, or wound culture. Those with mild symptoms are urged to drink liquids and stay hydrated. Those with more severe infections should receive antibiotics and be closely monitored, often involving hospitalization. Prevention of food-related V vulnificus infection involves avoidance of ingesting raw or undercooked seafood and the use of gloves and careful handwashing after handling raw seafood. Those with open wounds (including recent surgery, piercings, and tattoos) should avoid contact with brackish water (swimming, fishing, and wading) and should not handle raw seafood. Wounds or cuts that have been exposed to brackish water or uncooked seafood should be washed thoroughly with soap and water to decrease the risk of infection.

For more information go to www.cdc.gov

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