Food Poisoning and Parasites

Food poisoning from sushi can be caused by parasites such as anisakiasis or bacteria like vibrio or listeria. Symptoms may appear right away or within a few days, depending on what is causing the infection.

The only way you can completely avoid food poisoning from sushi is to avoid eating sushi prepared with raw or undercooked seafood. If you do choose to eat sushi made with raw fish, you can limit your risk by choosing reputable sushi restaurants and asking about a restaurant's food handling practices.

This article discusses the types of infectious diseases that could occur from eating raw fish in sashimi or sushi. It also covers symptoms to watch for and who is most at risk.

Anisakiasis

Anisakis simplex (herring worm) is a fish parasite that is often found in Pacific salmon, monkfish, herring, haddock, flounder, and fluke. Human infection by anisakiasis and other nematodes, or roundworms, can be caused by eating these fish raw or undercooked.

Ingestion of this tiny worm can result in severe abdominal pain, nausea, and vomiting within hours of eating. Even more, if the worms don’t get coughed up or vomited out, they can burrow into the walls of your intestines. This can cause a localized immune response, or inflammation, in the intestine.

If this does occur, the worms eventually die and are removed by the immune system. However, in severe cases, your doctor may need to remove them to reduce the pain. This could be done by surgery or by endoscopy, a flexible tube and camera that allows the doctor to see and remove them.

It is possible to kill anisakiasis by freezing the fish at minus four degrees or flash freezing it at minus 31-degree temperatures.

Vibrio

The bacterial species Vibrio parahaemolyticus is associated with eating raw or undercooked fish and shellfish, particularly oysters.

Infection can cause symptoms like diarrhea (including bloody diarrhea), abdominal cramps, nausea, vomiting, headache, fever, and chills. It can become severe in people with weakened immune systems. 

Another Vibrio species, Vibrio vulnificus, has been found in oysters, clams, and crab. In healthy people, ingestion of this microbe may cause nausea, vomiting, watery diarrhea, abdominal cramps, and fever.

In people with liver disease or weakened immune systems, the microbe can enter the bloodstream, causing a life-threatening whole-body infection. 

In addition, the Vibrio species can cause wound infections through open sores exposed to water harboring the bacteria. Examples include scrapes when opening oysters or working on boats. Like the gastrointestinal illness, these types of wound infections are most severe in people with impaired immune systems.

Listeriosis

Listeriosis is an infection caused by the bacteria Listeria monocytogenes. This bacteria can be found in raw seafood, unpasteurized milk and dairy products, vegetables such as raw sprouts, and other foods.

The biggest risk for listeriosis is in people who are:

• Pregnant
• Newborns (the bacteria can pass through the placenta)
• Older than age 65
• Have a weakened immune system

If you're not pregnant, listeriosis may cause mild symptoms like upset stomach and diarrhea. It may also cause flu-like symptoms such as:

• Fever and chills
• Muscle aches
• Headache

If the infection spreads to the nervous system, it can lead to meningitis, which is inflammation of the membranes and fluid around the brain and spinal cord. People with meningitis experience serious symptoms like stiff neck and confusion.

Listeria can also cause meningoencephalitis—inflammation of both the brain tissue and the membranes around the brain. Nervous system infection is most common in the immunocompromised and the elderly.

If you are pregnant, listeriosis may lead to a miscarriage, stillbirth, premature delivery, or a serious infection in the newborn.

Salmonella

Salmonella infection is caused by the bacteria Salmonella enterica. Infection with salmonella causes symptoms such as:

• Diarrhea
• Fever
• Stomach cramps

Some people may also experience nausea, vomiting, and/or headache, Symptoms often begin within one to three days of eating the contaminated food and can last up to seven days.

Salmonella infection can become serious, especially in infants, people over 65, or people with weakened immune systems. See a healthcare provider right away if you have salmonella symptoms along with a fever higher than 102 degrees, blood in your stool, or symptoms of dehydration.

Bacillus Cereus

Bacillus cereus is another foodborne illness associated with eating sushi. It's linked to eating contaminated rice along with other foods like fish, vegetables, meats, and milk.

There are two types of Bacillus cereus infections: a diarrheal type and a vomiting type. The diarrheal type develops quickly (within six to 15 hours) and causes the following symptoms:

• Watery diarrhea
• Moderate nausea

Most people with this type do not vomit or develop a fever. Symptoms usually resolve in 24 hours.

The vomiting type is associated with contaminated rice products. One example might be fried rice that has been sitting at room temperature for a long period.  This type tends to come on faster, within about one to five hours. It can cause:

• Nausea and vomiting
• Stomach cramps
• Diarrhea

Serious complications including meningitis can also occur.

Tips for Eating Sushi Safely

If food handlers do not use good hand hygiene, other infections (like norovirus, hepatitis A, and Staphylococcus aureus) can spread. Those who handle food should always wash their hands properly and stay home from work if ill.

When eating sushi in a restaurant, you can reduce your risk by choosing vegetarian sushi or sushi prepared with cooked fish. If you do choose to eat sushi made with raw fish, pick only reputable restaurants and ask about the practices and guidelines used to prepare your food.

If you are healthy, the risk of getting a serious illness from sushi is low. However, you should be aware that eating raw or undercooked fish always carries some risk. People in high-risk groups like infants and small children, pregnant people, older adults, people with liver disorders, and people with weakened immune systems are at much higher risk of serious illness and should avoid eating sushi made with raw or undercooked fish.

If you do get sick, most of these illnesses resolve on their own in a few days. Make sure to stay well-hydrated as you recover, and get plenty of rest. See a healthcare provider if you experience severe symptoms after eating sushi, such as vomiting that persists for longer than a few days, symptoms of dehydration, or blood in your stool.

Summary

It's possible to get an infectious disease when eating raw fish in sushi or sashimi. These could be caused by a worm, like anisakiasis, or a bacteria, such as Salmonella or listeriosis.

Many of these infections can cause digestive symptoms, including diarrhea, nausea, and vomiting. In some cases, they can lead to more serious conditions that require hospitalization.