Histamine poisoning
	Diagnosis
	Anaphylaxis
Histamine poisoning (sometimes called scombroid poisoning) is fairly unusual in its most severe form, although mild examples of it are not uncommon.  In the severe form, several people who eat the same seafood meal fall ill with symptoms that suggest severe seafood allergy.

Histamine and other amines are formed by the growth of certain bacteria and the subsequent action of their enzymes on certain amino acids in food, either during the production of a product such as Swiss cheese or by bacterial spoilage of foods such as fishery products, particularly fish that belong to the family Scombridae such as tuna, mahi mahi, bluefish, sardines, mackerel, amberjack, and abalone. However, any food that contains the appropriate amino acids and is subjected to certain bacterial contamination and growth could lead to scombroid poisoning when eaten.

Initial symptoms may include a tingling or burning sensation in the mouth, a rash on the upper body and possibly faintness.  Frequently, headaches and burning or itching of the skin are encountered.  The symptoms may progress to nausea, vomiting, and diarrhoea and can even require hospitalisation, particularly in the case of elderly or frail patients.  Whilst isolated episodes in single individuals can occur (mild attacks often go unrecognised), outbreaks of typical symptoms affecting several people that have eaten the same contaminated product have occasionally been reported. 

Diagnosis

Diagnosis of the illness is usually based on the patient's symptoms, time of onset, and the response to treatment with antihistamine medication.  If the condition is suspected at the time, it is possible for the implicated food to be analysed within a few hours for elevated levels of histamine to confirm a diagnosis.

Fishery products are particularly commonly implicated in scombroid poisoning; particularly those from the Scombridae family including tuna, mahi mahi, bluefish, sardines, mackerel, amberjack, and abalone.  However other foods can occasionally cause a similar effect, for example certain cheeses and soya bean curd (tofu).  The toxin forms in a food when certain bacteria are present and time and temperature permit their growth.  Distribution of the toxin within an individual fish fillet or between cans in a case lot can be uneven, with some sections of a product causing symptoms and others not.   Neither cooking, nor canning or freezing reduces the toxic effect.  Examination by the consumer cannot ensure the absence or presence of the toxin, although it seems likely that odorous fish is more likely than non-odorous fish to cause a problem.

Recognition

Such reactions often go unrecognised or unreported because of a lack of understanding of the condition, and confusion with the symptoms of other illnesses such as food allergy.  The onset of symptoms can be rapid, ranging from immediate to 30 minutes.  The duration of the illness is usually three hours, but may last several days.  Patients may need tests of true food allergy (for example to fish) to exclude this as an explanation for symptoms and to reassure the patient that the blamed food need not be avoided in future.

All humans are susceptible to histamine poisoning; however it does appear that some individuals may be more histamine-sensitive than others.  Taking alcohol at the same meal can increase the chance of a reaction and the symptoms are likely to be more severe for the elderly and for those taking the following medications: