Sweden has reported three outbreaks of histamine poisoning in tuna from Vietnam in the past three months.

The outbreaks, which have affected about 60 people, do not appear to be directly related as the tuna originated from different batches. Patients are from different municipalities in southern and central Sweden.

Symptoms were typical for histamine poisoning and included swelling, hives, irregular heartbeat, nausea, diarrhea and vomiting.

Timeline of outbreaks
In the latest outbreak, which began in early July, involving histamine in thawed tuna from Sweden, with frozen raw material from Vietnam, about 20 people from five different municipalities fell sick after eating tuna from the same batch. Most of them had bought the fish in retail stores.

Patients in the second outbreak caused by histamine in frozen vacuum-packed yellowfin tuna loins from Vietnam, via the Netherlands, were reported from May 29 to June 12. Nine people that had eaten tuna from the same batch at three different restaurants in two different municipalities were affected.

The earliest outbreak in May was due to histamine in frozen yellowfin tuna loins from Vietnam, also via the Netherlands. All 30 reported cases had consumed a dish with tuna at the same restaurant.

This batch was produced by one of the larger operators in Vietnam, which supplies several wholesalers in Europe. It was produced in June and shipped in July 2019 and only distributed within Europe.

Local authorities are responsible for the outbreak investigation and tracing food batches. The Swedish Food Agency (Livsmedelsverket) is the national contact point for Europe’s Rapid Alert System for Food and Feed (RASFF).

In 2020, histamine in fish from Vietnam has been responsible for six reports on RASFF. The three outbreaks from Sweden and another alert in May from the same country about histamine in frozen tuna loins. In January, Portugal issued a border rejection for frozen tuna belly with skin due to histamine levels and in June, Hungary warned of histamine in thawed yellowfin tuna fillets from Vietnam via Slovenia.

Problem outside of Sweden
Mats Lindblad, from the Swedish Food Agency, said investigations started due to reports of food poisoning. During the enquiries, high levels of histamine in tuna were confirmed in all three outbreaks.

“It is always necessary to keep tuna well chilled, but no particular advice has been issued to food business operators in Sweden due to the outbreaks because in this case the high levels of histamine arose before the implicated batches were brought into Sweden,” he said.

“No restrictions have been placed on fish from Vietnam. But considering that high levels of histamine in tuna from different countries frequently are reported, it is of course important that producers of tuna make further efforts to avoid the problem.”

Onset of histamine food poisoning symptoms can range from minutes to several hours following ingestion of toxin. Typically, the average incubation period before illness is one hour.

The most common symptoms of histamine, or scombroid fish poisoning, are tingling or burning sensation in the mouth, facial swelling, rash, hives and itchy skin, nausea, vomiting or diarrhea. They usually resolve within several hours without medical intervention.

Production of histamine is related to mishandling of food due to storage at incorrect temperatures. Once histamine has been produced, it cannot be eliminated by normal cooking or freezing temperatures.

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