In Australia a report that six people suffered scombroid fish poisoning after eating in a Japanese restaurant has sparked a public health warning.
The latest issue of the journal Emergency Medicine says the six people fell ill, but all recovered, after eating spiced tuna steaks with wasabe at the restaurant in Canberra last year. The fish had been bought from a Sydney fish market.
Michael Hall, a staff specialist in emergency medicine at The Canberra Hospital, said there had only been three reported cases of scombroid poisoning or histamine poisoning in Australia prior to his report. However, he said he believed the condition was "massively under-reported", because people often wrote it off as food poisoning or gastroenteritis.
Scombroid, also known as histamine poisoning, occurs when bacteria breaks down muscles in the fish, causing the release of toxins. The process can occur at any stage between getting the fish from the ocean to the table. But it is almost impossible to get scombroid poisoning from eating fish straight from the boat.
The toxin is most commonly produced in dark skinned fish like tuna, sardine and mackerel when there is inadequate refrigeration.
"That can be at any stage of the process - the initial catching, at the fish markets, at the restaurant," Dr Hall said.
Symptoms usually occur within four hours of eating the fish and include tingling or burning sensations in the mouth, a rash on the face and upper body, throbbing headache, hives or itchy skin, nausea, vomiting and diarrhea.
Symptoms can last for several days but usually disappear within 12 hours.
Dr Hall said it was impossible to tell from the look or smell of a fish if it was contaminated and the toxins were not removed by cooking.
However, affected fish could have a "peppery" or bitter taste, he said. "The fish looks fine, it smells fine, you can't see the little bacteria festering around," he said. "It's said to have a very strong bitter and peppery taste ... but the patient that got sickest said he actually quite liked the flavor and ate the whole thing.
"Generally, if you detect a peppery taste in unspiced fish you should stop eating it."
An outbreak of scombroid poisoning from dried fish in Japan some years ago affected 5,000 people, Dr Hall said. Between two and three per cent of fish in some European markets have been found to be contaminated, he said.