types of food poisoning, scombroid form is not brought about by ingestion of a pathogen. Histidine is an amino acid that exists naturally in many types of food, including fish. At temperatures above 16 °C (60 °F), histidine is converted to the biogenic amine histamine via the enzyme histidine decarboxylase produced by symbiotic bacteria such as Morganella morganii (this is one reason why fish should be stored in the freezer). Histamine is not destroyed by normal cooking temperatures, so even properly cooked fish can still result in poisoning. Histamine is the main natural chemical responsible for true allergic reactions, so the symptoms produced are almost identical to a food allergy. Rarely, cheese may be involved. Diagnosis Differentiating scombroid from a fish allergy can be difficult, as both present with similar symptoms. In scombroid, blood tryptase is generally normal, while in an allergic reaction, it is elevated. Prevention Cooking, smoking, canning, or freezing will not destroy histamine in contaminated fish. Antihistamines may also be taken before eating seafood. Treatment Treatment is in the form of supportive care. If light-headedness occurs, a person should lie with feet partly elevated. Antihistamines such as diphenhydramine (H1 blockade) and ranitidine (H2 blockade) together with intravenous fluids may help with mild to moderate symptoms. Epinephrine combined with a steroid may be used for severe symptoms. Epidemiology Isolated reports of scombroid food poisoning in humans caused by histamine present in the tissues of stale or rotten scombroid fish, usually tuna, have occurred over the years. In September 2016, authorities in Singapore intercepted canned tuna imported from Thailand after finding high levels of histamine. No human cases were reported. In 2015, seven people at a cafe in Sydney became ill after eating John Bull Tuna Chunky Style in safflower oil on tuna salads. The tinned tuna had come from Thailand. The Shenzhen Post reported that histamine poisoning from scombroid fish happens often in the autumn in Guangdong province in China. In August 2013, 26 people in Shenzen were poisoned after eating stale mackerel. Several people became ill after eating tuna sandwiches at a cafe in Edinburgh in Scotland in 2013. The tuna had come from Ghana. In 2011, 20 reports of food poisoning at a Stockholm restaurant were thought to be histamine poisoning in tuna from Senegal. In 2012, UK environmental health authorities in north east Lincolnshire intercepted and destroyed a shipment of tuna from Vietnam after four