Infectious Diseases Associated with Eating Sushi

Fishing for Worms

Sushi. Steven Errico/Getty Images

Sushi, it's a popular food. In Japan, it’s part of the national diet. In the US, it's a favorite for many. It's often considered a special treat to be able to eat sushi.

Sushi actually refers to the small balls or rolls of vinegar-flavored cold cooked rice which is garnished with vegetables, egg, raw fish, or other foods. It doesn't have to include raw fish. It's “sashimi” that is sliced raw fish. That said, sushi often includes raw fish.

It's a special treat to have and it's often an expensive meal. But is there any risk we should be aware of? 

Risks of eating raw fish

Anisakis and other parasites

Human infection by Anisakis simplex (herring worm) and other nematodes, or roundworms, can be caused by eating certain raw or undercooked fish. Ingestion of the tiny 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 (which may require prolonged treatment) 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.

Other infections

There are other infections that have been tied to sushi. Listeria, which is particular risk for pregnant women and the immunocompromised, has been considered a risk with sushi. There have also been infections with salmonella and norovirus which have been tied to sushi. Infections can also be spread if sushi is not prepared by food handlers who have good hand hygiene.

There are many infections (like norovirus and hepatitis a and many diarrheal illnesses) that can spread if those who handle the food are sick and do not wash their hands properly (or stay home from work if ill).

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). There are other cases that have been found in Japan but also Europe, South America, and other areas of the world. 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 foodborne infections and should more carefully consider what they eat. With sushi, it would be important that the fish came from a reputable source if eaten. At the same time, others avoid fish during pregnancy for other reasons, like mercury levels. This is something to talk to your doctor or other healthcare provider about, as it's important not just to stay safe but also not to limit yourself more than you should.

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 Information Division of Foodborne, Bacterial, and Mycotic Diseases. CDC.

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

Listeria 

Salmonella

Norovirus

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