Scombroid food poisoning in fish
Scombroid poisoning is caused by accumulated bacteria that turn histidine into scombrotoxin (histamine) in improperly stored fish.

Scombroid poisoning (scombroid food poisoning or scombroid) is a foodborne illness that is typically caused by consuming spoiled fish, which contains a chemical called histidine. Bacteria can multiply in fish when stored at warm temperatures (59°F) and turn histidine into scombrotoxin (histamine). Histamine is responsible for the symptoms of scombroid poisoning.

Cooking the fish can destroy the causative bacteria but cannot reduce histamine levels. The amount of histamine in the meat varies depending on the part of the spoiled fish. Hence, everyone who eats the meat may not be affected by scombroid poisoning.

Scombroid poisoning does not happen because of an infection or allergy. It is safe to eat the same kind of fish again if it is freshly caught and stored chilled.

This condition is more common in certain types of fish, which have dark meat and a naturally higher level of histidine, such as:

  • Tuna
  • Mackerel
  • Sardine
  • Butterfly kingfish
  • Marlin
  • Herring
  • Bluefish
  • Amberjack
  • Anchovy

Since these fish have higher levels of histidine, there is a higher risk of it being converted to histamine when bacterial growth occurs, resulting in scombroid poisoning. Occasionally, other species of fish may be responsible.

What are the signs and symptoms of scombroid poisoning?

Symptoms of scombroid poisoning usually appear within 10 to 30 minutes of ingesting the fish and can last for about 10 to 14 hours, rarely lasting longer than a day or two. Those with asthma may be at risk of more serious problems.

Initial signs and symptoms (these may resemble an allergic reaction):

Other signs and symptoms:

  • Facial rash or over the torso and rest of the body
  • Intense itching along with a rash
  • Generalized edema (water retention and swelling of the body)
  • Diarrhea, which is typically short term
  • Abdominal cramps

Serious signs and symptoms:

In extremely rare cases, scombroid poisoning may result in death.

How is scombroid poisoning diagnosed?

Doctors can make a clinical diagnosis based on history (such as recent fish consumption) and clinical examination. As scombroid poisoning can present symptoms similar to allergic reactions, your doctor may prescribe certain tests.

Blood tryptase levels may also be done. These levels would be elevated during an allergic reaction and normal in scombroid poisoning.

How is scombroid poisoning treated?

Scombroid poisoning is often self-limiting and the symptoms rarely last more than a day or two, so treatment is mainly supportive. Those with giddiness are advised to lie down and rest with their feet partly elevated.

Administering antihistamines, such as H1 blockers and ranitidine (an antacid or H2 blockade), along with intravenous fluids can help those with mild to moderate symptoms to recover faster. In severe cases, epinephrine combined with a steroid may be used.

How to prevent scombroid poisoning

Cooking, smoking, canning or freezing will not destroy histamine that has already formed in the fish. The best way to prevent scombroid poisoning is by ensuring the fish is caught fresh and stored chilled. Antihistamines may be taken before eating seafood if the source and storage of the fish are not known, especially while eating out.

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Medically Reviewed on 8/4/2021
References
U.S. Food and Drug Administration. Scombrotoxin Poisoning and Decomposition. https://www.fda.gov/food/seafood-guidance-documents-regulatory-information/scombrotoxin-poisoning-and-decomposition

American Academy of Allergy, Asthma & Immunology. Histamine Toxicity. https://www.aaaai.org/Conditions-Treatments/Related-Conditions/histamine-toxicity

Marcus EN. Scombroid (Histamine) Poisoning. UpToDate. https://www.uptodate.com/contents/scombroid-histamine-poisoning

Hungerford JM. Scombroid poisoning: A review. Toxicon. 2010; 56(2): 231-243. https://www.sciencedirect.com/science/article/abs/pii/S0041010110000450