• IV, vitals and monitor to assess for anaphylaxis while obtaining history.
• When in doubt, treat with IM Epinephrine and antihistamines.
• Determine if the patient has any allergies and what they consumed prior to the symptom onset.
• Assess if the patient ingested fish and if there are other patients with similar symptoms and onset suggestive of scombroid toxicity.

• Not a true allergy but a pseudo-allergy.
• Generally considered benign; has caused death, coronary spasm, ventricular fibrillation and persistent hypotension (extremely rare; ONE case report).
• Ingestion of dark meat or scombroid type fish (tuna, mackerel, mahi-mahi, marlin) leads to histamine poisoning from ingestion of heat and cold stable preformed histamine toxin.
• Rarely anchovies, greater amberjack fish, swordfish, herring, sardines, salmon, trout, and Swiss cheese.
• When improperly stored at temps over (>4°C), large amounts of histamine are produced in the decomposing fish by conversion of histidine into histamine by enzyme produced by bacteria.
• Most commonly occurring in the summer, can develop toxin at any time in the preparation process as is not killed by cooking, freezing or canning.
• Drugs that inhibit histamine metabolism will cause worsening symptoms, such as Monoamine oxidase inhibitors (MAOIs) or isoniazid.

• A clinical diagnosis.
• Symptoms occur within minutes to 1 hour of consuming scombroid fish.

Symptoms: Burning pepper taste in the mouth and throat, flushing of the face and neck or over heating sensation, edema, face, eyes, intra oral, skin surface, headache, diaphoresis, generalized pruritus, palpitations and nausea.

Signs: Flushing, edema, urticaria, vomiting diarrhea, tachycardia, hypotension. Rarely chest pain, respiratory distress, bronchospasm and distributive shock.

• Responsive to antihistamines, not as responsive to epinephrine as anaphylaxis.
• Not IgE mediated and tryptase negative.
• Rarely, the fish can be tested for histamine levels. Enzyme ripened products ≥20 mg/100g is diagnostic according to the BC CDC.

• Anaphylaxis: Difficult to distinguish other than history of concurrent patients, prior allergy history.
• Allergic reaction is more likely if other people who consumed the same fish do not exhibit similar symptoms to the patient.
• Myocardial infarction: Histamine can cause coronary vasospasm and can present similarly to ACS. In rare cases, advanced cardiac imaging may be required to differentiate.
• Shellfish poisoning: more latent course and involves paresthesia and neurological findings (e.g., paralysis).
• Other Flushing Disorders (Mast Cell Activation Syndrome, Carcinoid Syndrome, Pheochromocytoma): Will demonstrate tryptase and urinary prostaglandin metabolites, 5-HIAA, or urinary metanephrines respectively.
• Niacin ingestion, ETOH-disulfiram reaction.
• Gastroenteritis: abdominal pain, vomiting and diarrhea can be the initial symptoms due to vasodilation and increased capillary permeability.

• If in anaphylactic shock: Epinephrine 0.3-0.5mg IM.
• Antihistamines H1 and H2 blockers are the main stay of treatment plus supportive care.
• H1 options: Loratadine 10mg po or Benadryl 25-50mg IV.
• H2 options: Cimetidine 200-800 mg po (particularly for GI symptoms.)
• IV fluids if moderate-severe hypovolemia from vomiting or diarrhea.
• Steroids do not have benefit.

• Typically self-limiting but up to 48 hours.
• Admission may be required if severe.
• Assess for complications such as coronary vasospasm.
• Patients with mild symptoms or who demonstrate a rapid response to antihistamines can be discharged home.
• Notify public health of food borne related illness.
• There are no reported cases of rebound histamine release.

1. BC CDC Patient Handout:

   http://www.bccdc.ca/resource-gallery/Documents/Educational%20Materials/EH/FPS/Fish/Scombroid%20Fish%20Poisoning%20Nov13.pdf

   
   

2. Recommended URLs:

   Scombroid Poisoning

   
   

1. Stratta P, Badino G. Scombroid poisoning. CMAJ. 2012;184(6):674. doi: 10.1503/cmaj.111031.

   
   

2. Feng C, Teuber S, Gershwin ME. Histamine (Scombroid) Fish Poisoning: a Comprehensive Review. Clin Rev Allergy Immunol. 2016;50(1):64-69. doi: 10.1007/s12016-015-8467-x.

   
   

3. Attaran RR, Probst F. Histamine fish poisoning: a common but frequently misdiagnosed condition. Emerg Med J. 2002;19:474-475.

   
   

4. Katugaha SB, Carter AC, Desai S, Soto P. Severe scombroid poisoning and life-threatening hypotension. BMJ Case Rep. 2021;14(4):e241507. doi: 10.1136/bcr-2020-241507.

   
   

5. Tortorella V, Masciari P, Pezzi M, Mola A, Tiburzi SP, Zinzi MC, Scozzafava A, Verre M. Histamine Poisoning from Ingestion of Fish or Scombroid Syndrome. Case Rep Emerg Med. 2014;2014: 482531. doi: 10.1155/2014/482531