The risk of histamine food poisoning — also known as scombroid fish poisoning — could increase in Europe in the future if trading trends continue, according to researchers.

The scientists made the remark in the journal Eurosurveillance during an investigation into a 2017 outbreak in France linked to tuna.

Histamine contamination generally occurs because of inadequate refrigeration of fish, and can occur at any stage of the food chain. Once formed, it is not destroyed by cooking, smoking or freezing.

The risk of histamine food poisoning (HFP) could increase in the coming years, the researchers predict, because European fresh tuna imports went up by 5 percent per year on average between 2011 and 2015. If the trend continues, the incidence of poisoning will likely follow it.

According to the European Food Safety Authority (EFSA) and European Centre for Disease Prevention and Control (ECDC), 599 HFP outbreaks were reported in the European Union during 2010 to 2017. HFP peaked in 2017, with 117 outbreaks involving 572 patients, mainly reported by France and Spain.

Italy has made the last 10 alerts for scombroid poisoning in fish from Spain, Sri Lanka or India since 2010 in the RASFF portal with the most recent this month. Ten notifications this year have mentioned histamine.

National surveillance in France shows HFP accounted for 3.6 percent, or 263 out of 7,346, of foodborne outbreaks reported between 2010 and 2016. Of these, only 62 were confirmed in the laboratory, which underlines the difficulties of investigation.

Histamine food poisoning is an allergy-like reaction caused by eating fish or fermented foods containing a high concentration of histamine. Scombroid fish such as tuna and mackerel, as well as some non-scombroid fish such as mahi-mahi, sardines, pilchards, herring, are commonly implicated.

French histamine outbreak
In April 2017, an outbreak of histamine poisoning occurred in a French military unit near Paris. A total of 40 cases were identified among the 241 people who had eaten at the catering facility.

The median age of cases was 38 years, with an overall range of 18 to 58 years old. Sixty-eight percent, of 21 of 31, were men. Common symptoms were headache, hot flushes, rash, nausea, palpitations and diarrhea. Six patients were hospitalized, all for less than a few hours.

“In this outbreak, the initial onset of symptoms in two food handlers could have alerted staff early on; however, their symptoms were, to them, unexpected for a foodborne outbreak and therefore were not immediately associated with the tuna,” said researchers.

Researchers conducted a case-control study on 31 cases and 63 control subjects. Among cases, 30 had consumed tuna, whereas only 12 of 63 control subjects had.

Multivariate analysis pointed to cooked yellowfin tuna fillets as the likely source of food poisoning. HFP was quickly suspected because of the allergy-like symptoms of the patients, rapid onset after a meal, and consumption of the tuna. As soon as it was suspected, the remaining uncooked tuna was withdrawn from the military catering facility.

Fresh yellowfin tuna was from Reunion Island and was supplied vacuum-sealed and packed with ice at the principal food market of Paris. No cold chain issues could be established in the upstream and downstream supply chains.

Trace back investigation
One screening test by the local supplier in Reunion before transport to France found the histamine concentration to be less than 200 milligrams per kilogram.

Histamine concentration was found to be 1,720 mg/kg in leftover raw tuna, and 3,720 mg/kg in control samples of cooked tuna, well above the threshold limit values defined by European regulations of 200 mg/kg.

Presence of Klebsiella variicola and Pantoea agglomerans, microorganisms of the Enterobacterales order reported to produce histamine, was confirmed in leftover raw tuna.

“Concentration may vary in the flesh of one tuna or between different fish in one batch. This could explain why not all people who ate the tuna became sick and why the analysis by the local supplier in Reunion was normal,” wrote researchers.

Recorded temperature values could be traced from the fishing boat to the self-catering military facility; they complied with the regulatory requirements of between 0 degrees C and + 2  Celsius for raw fishery products.

Assessment of the catering process and facilities did not highlight deviation from food storage and hygiene practices. No abnormal odors or changes in appearance of the tuna were observed by the cooks.

Researchers assumed that contamination may have occurred early in the fishing phase, including time spent in the water after death, or during initial preparation of the fish, such as cutting and evisceration.

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