Scombroid poisoning: bacterial histamine production in seafood

Scrombroid poisoning also known as histamine poisoning, is the most common form of seafood toxicities. As per the CDC statistics, histamine poisoning accounts for 37% of all seafood related poisoning and 5% of all food related toxicities. [Daniel Noltkamper] Scrombroid poisoning occurs due to the metabolic conversion of histidine, a natural amino acid found in the fish flesh into the toxic histamine by the activity of bacteria. This occurs most rapidly when the fish are exposed to ambient temperatures of 21.1°C-32.2°C for a few hours, or even at temperatures greater than 7.2°C. Since majority of the seafood consumed in the United States is imported from abroad, the FDA had implemented quality control standards in 1995 known as the Hazard Analysis Critical Control Point (HACCP) to check the quality of all imported seafoods. However, as the 2003 statistics showed, barely 5 to 7% of all imported seafoods from more than 8500 importers were checked for the HACCP standards. [CDC] the fact that not all foreign and local fishing boats are covered under the HACCP implies that the risk of outbreak of scromboid poisoning is quite real and a concerning problem. Let us have a brief overview of scrombroid poisoning, its cause, symptoms, treatment and the preventive measures to avoid this fish poisoning.

Current Understanding

Scrombroid poisoning was thought to be caused by the consumption of putrefied fish belonging to the families of Scombroidae and Scomberesocidae such as mackerel, tuna, swordfish, albacore, etc. However, today we understand that dark skinned nonscromboid fishes such as amberjack and mahimahi also cause histamine poisoning. [Gerry predy] Today we know that Histidine decarboxylase (HDC) present in Escherichia coli, Proteus, Klebsiella and other species of bacteria is the main causative agent for histamine poisoning as it converts the histidine amino acid into toxic histamine when exposed to room temperature for a few hours. These bacteria live on the fish tissues and under favorable conditions (high temperature) multiply and metabolize histidine to histamine. It is estimated that histidine to histamine ratio which is usually 0.1 mg/100 g in a healthy living fish can quickly shift to 100 mg/100 g. [Daniel Noltkamper] We now know that anything that exceeds 20mg/100g for histidine histamine ratio is a toxic dose. However, there is still much to be uncovered about the mechanism of toxicity, as laboratory attempts to recreate symptoms by oral intake of toxic levels of histamine, have failed. This in spite of the fact that patients administered with anti-histamines tend to respond well and recover from the symptoms indicates a possible role of other agents. It is postulated that symptoms manifest when histamine combines with other biological amines. [Marta Ferran] People affected by scromboid poisoning may present with symptoms ranging from heachache, vomiting, skin rashes, palpitations, to urticaria and acute bronchospasm in severe cases. Though mortality is very rare immediate and efficient management of symptoms is of utmost importance in order to avoid any serious complications from developing.

Conclusion

Scrombroid poisoning is a leading case of seafood poisoning and is easily preventable. Since histamine is heat stable, it is important to realize that heating would not make contaminated fish fit for consumption. Strict adherence to HACCP standards (storage under