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Sushi Scares - Infectious Diseases Associated with Eating Sushi or Raw Fish

Fishing for Worms

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Updated April 15, 2009

Sushi Scares - Infectious Diseases Associated with Eating Sushi or Raw Fish

Sushi

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In Japan, it’s part of the national diet. In the U.S., it has grown in popularity since the late 1970s. Sushi, often mistaken for its counterpart “sashimi”, which is sliced raw fish, is actually a sweetened vinegared rice usually combined with other ingredients, including raw fish. While this delicacy is now enjoyed worldwide, there is also growing concern about the risk of infections from consuming raw fish.

Risks of eating raw fish

Anisakis and other parasites

Human infection by Anisakis simplex (herring worm) and other nematodes, or roundworms, is caused by eating certain raw or undercooked fish. Ingestion of the worm can result in severe abdominal pain, nausea, and vomiting within hours of ingestion and has been misdiagnosed as appendicitis or other stomach diseases. If the worms don’t get coughed up or vomited out, they can burrow into the walls of your intestines and cause a localized immune response. The worms eventually die and are removed by the immune system. In severe cases, physical removal of the worms by endoscopy or surgery is needed to reduce the pain. They can in rare, severe cases cause anaphylactic shock as well. Albendazole may be used to treat mild cases.

Vibrio species

The bacterial species, Vibrio parahaemolyticus has been associated with consumption of raw or undercooked fish and shellfish, particularly oysters. Infection by these bacteria can cause symptoms including diarrhea, abdominal cramps, nausea, vomiting, headache, fever, and chills. The infection is usually self limiting and typically does not require antibiotics.

Another Vibrio species, Vibrio vulnificus, has been found in oysters, clams, and crab. In healthy people, ingestion of this microbe can cause vomiting, diarrhea, and abdominal pain, but in people with liver disease or weakened immune systems, the microbe can enter the bloodstream, causing the life-threatening condition of septicemia.

Gastroenteritis from Vibrio vulnificus is rare, but it can happen on occasion. Rather, these microbes are more commonly associated with wound infections through open sores exposed to water harboring the bacteria. Examples include scrapes when opening oysters or working on boats. These types of wound infections are most severe in people with weakened immune systems.

Should I avoid sushi?

The risk of eating raw or undercooked fish in the U.S. is very small, with fewer than 10 cases of Anisakis infection diagnosed each year (although many cases are likely unreported). In addition, the FDA has provided several guidelines for retailers who sell fish intended to be eaten raw. These guidelines include freezing the fish to -31°F for 15 hours or -4°F for 7 days to kill parasites and physical examination known as “candling” for the presence of worms.

Who should avoid raw fish?

People with liver disorders or weakened immune systems (i.e. small children, the elderly, and pregnant women) have a greater risk for more severe outcomes from infection and should practice discretion when eating at a sushi bar.

Sources:

Anisakiasis. Laboratory of Identification of Parasites of Public Health Concern. CDC Division of Parasitic Diseases.

Anisakis simplex and related worms. USFDA Bad Bug Book. Center for Food Safety and Nutrition.

Sakanari JA and McKerrow JH.Anisakiasis. Clinical Microbiology Reviews 1989;2:278.

Parasites. Fish and Fisheries Products Hazards and Controls Guidance. FDA Center for Food Safety and Applied Nutrition. June 2001.

Vibrio vulnificus General InformationDivision of Foodborne, Bacterial, and Mycotic Diseases. CDC.

Vibrio parahaemolyticus. USFDA Bad Bug Book. Center for Food Safety and Nutrition.

Related Video
Basic Sushi Etiquette
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