Pathophysiology, Diagnosis & Treatment of Scromboid Fish Poisoning

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Written by:    George Schroeder MD, MS, FACEP, FAAUCM Clinical Assistant

                      Professor of Emergency Medicine UCF College of Medicine, Orlando, Florida



Scombroid ichthyotoxicosis or Scombroid fish poisoning consists of seafood-related food-borne illness resulting from the human consumption of improperly preserved, and/or inadequately refrigerated fish contaminated with histamine. Fish in the Scombroidae family (tuna, swordfish, mackerel, anchovies, sardines, skipjack and bonito) are the most common offenders; whereas other marine species such as mahi mahi, bluefish, marlin, amberjack and escolar are less frequently implicated.

In the event of such affected fish species not having been properly and continuously refrigerated, bacteria metabolize histidine and convert that substance to histamine which combines with other potentially toxic amines to form Scombrotoxin. Histidine decarboxylase (HDC), found in E. coli, Proteus and Klebsiella bacteria can convert histidine to histamine. In the absence of adequate prompt cooling (leaving fish @ room temperature for 12 hours) the bacteria proliferate and increase the histidine-to-histamine conversion rate, and may increase histamine levels from 0./mg/100 grams in healthy fish to 100 mg/ 100 grams of fish. Toxic levels generally exceed 20mg / 100 grams. Most patients present within 15-60 minutes of toxin ingestion. Variable effects due to individually differing rates of decay in each patient may cause different symptoms among people who ate the same seafood meal.

Histamine is heat resistant and can lead to Scombroid fish poisoning, even if fish is properly cooked or even canned. If more than 50 (ppm) of histamine is present in tissue of fish it indicates decomposition of fish, even though gross evidence of spoilage, such as putrid bad odor, may be absent or imperceptible. Toxic levels commonly exceed 200 ppm or greater than 500 ppm. A ‘honey-combed’ appearance may be evident on the cooked surface of the fish, which has also been documented in cases of histamine toxicity.



Increased levels of histamine in the urine of patients, along with increased levels of histamine in the tissue of the fish, confirm histamine as the causative agent in scombrotoxism. Most patients report a metallic, peppery taste, and in some cases even a mild bitter taste.

Symptoms of histamine fish poisoning may also include:

  • Flushing of skin, with deep confluent erythema unusually on upper body, and exacerbated by ultraviolet light or tanning beds.
  • Throbbing generalized headache
  • Nausea and vomiting
  • Diarrhea
  • Generalized abdominal cramps, following initial Epigastric pain
  • Pruritus of skin, hives (without wealing or skin swelling)
  • Palpitations, an unusual “thumping, pounding heart sensation”
  • Dizziness, lightheadedness, blurred vision
  • Dry mouth, swelling of tongue and face
  • And rarely chest tightness and possibly even dyspnea, leading to respiratory distress, in the presence of other comorbidities; such as bronchial asthma
  • Occasionally patients experience hypotension.
  • Symptoms appear to be more intense in patients taking certain medications that slow the breakdown of histamine by the liver such as INH (Isoniazid) and Doxycycline.


Pathophysiology, Diagnosis & Treatment of Scromboid Fish Poisoning

Laboratory Diagnosis

Urocanic acid (UCA) has been postulated as a complementary agent implicated in Scombroid fish poisoning, due to its effect on Mast cell degranulation. Chromatographic methods in lab have been used in Malaysia for simultaneous identification of trans- and cis-urocanic acid in fish samples. High concentrations of trans-UCA isomer were identified in histidine-rich dark-muscle fish. This chromatographic HPLC method was developed in Asia, showed a rapid, sensitive and accurate method with short retention time for expedient separation of urocanic acid isomers in fish samples.


The majority of cases of Scombroid Fish Poisoning are self-limited and last less than 6 hours. Active clinical monitoring of patients vital signs, especially Blood Pressure and respiratory rate along with symptomatic therapy are strongly recommended.

  1. Recent ingestion of contaminated fish, within less than 1 hour-one may consider gastric decontamination, however ipecac and gastric lavage are associated with their own complications and hazardous potential consequences.
  2. IV fluid and electrolyte replacement, commensurate with fluid and electrolyte loss due to recurrent emesis and diarrhea as well as perspiration associated with flushing.
  3. IV antihistamines (Hiaswellas HZ blockers)
  4. IV Steroids-particularly in the event of tongue and mouth swelling and edema
  5. Treatment of bronchospasm with nebulized beta-adrenergic agents and supportive oxygen therapy and ensuring adequate airway management.
  6. Treatment of Hypotension, in rare cases, with I.V. fluids, crystalloids and very rarely with I.V. pressers/inotropic agents.
  7. Analgesics for severe throbbing headache
  8. Anti-pruritic agents (such as Cetirizine, Loratadine and Fexofenadine), anti-emetics for symptomatic relief

The most informative patient discharge instruction sheet for Scombroid fish poisoning reviewed in the medical literature as a sample for prospective use:

In grateful acknowledgment for technical assistance in collaboration with Dr. John Spallino, Tampa, FL.



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Thank you for this throrough review of Scromboid Fish Poisoning from Dr. Schroeder. We look forward to collaborating with the AAUC on future research projects.”

– JFSEM Editorial Staff

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