Domestic beef and imported turkey cause the most Salmonella infections in Finland, according to results from a statistical model developed by the Finnish Food Authority (Ruokavirasto).

Potential origins of foodborne Salmonella infections in consumers were assessed based on information from between 2008 and 2015. During this time, the annual number of cases halved from about 3,000. Infections acquired in Finland varied from 300 to 400 cases.

Food categories studied included chicken and turkey meat, beef and pork. Finnish and imported meat were examined as separate categories, according to the study published in the Risk Analysis journal.

The domestic beef and imported turkey result is explained by the distribution of Salmonella subtypes rather than gross exposure. Gross exposure from domestic beef was not particularly large, and only minor from imported turkey. However, a wide selection of subtypes were detected in these sources during surveillance.

The Bayesian source attribution model used combined microbial subtyping and comparative exposure assessment with sparse isolate data. Source attribution provides guidance for risk management.

Antti Mikkelä, a researcher from the Finnish Food Authority, said turkey meat imported into the country showed the highest value as a source of infection.

“Based on the research material, about two thirds of annual human Salmonella infections of Finnish origin represent subtypes of Salmonella that were also identified in the studied food categories,” she wrote. “As evaluated by using the model, three subtypes of Salmonella with the relatively highest risk levels were Enteritidis 8, Newport and Enteritidis 1b.”

Most common serotypes
The number of different Salmonella subtypes detected in foods or food production animals, specifically chickens, turkeys, cattle and pigs, during the eight‐year period was 86, of which 17 were not found in humans in 2008 to 2015.

A total of 54 of the 86 subtypes were only detected in one source. The remaining 32 were found in two or more sources. Enteritidis 8, Newport, Enteritidis 1b, Enteritidis 1, and Virchow were relatively common in humans during the surveillance. Salmonella Newport was uniquely isolated from imported turkey, and subtypes Typhimurium 1 and Typhimurium NST were estimated to be relatively common in domestic beef.

Overall, 2,767 domestic salmonellosis patients were registered during 2008 to 2015 and 67.1 percent of reported cases were confirmed to represent Salmonella subtypes also found in one or more of the sources looked at during the study period.

The method compares subtypes of Salmonella diagnosed in humans to those in foodstuffs and production animals while accounting for the occurrence of Salmonella in food and volume of consumption. It is used to describe and evaluate the differences between risk levels of various subtypes and food categories.

Annually, from 55.7 percent to 77.4 percent of human cases represented the same Salmonella subtypes as isolates found in some of the studied sources during the eight‐year period. The remaining cases were attributed to unknown sources.

Proportion of the total Salmonella disease burden attributed to different sources was estimated to be 14.4 percent domestic beef; 9.8 percent imported turkey meat; 10.4 percent imported pork; 9.3 percent domestic pork; 9.9 percent imported chicken meat; 5.7 percent imported beef; 5.2 percent domestic turkey; 2.2 percent domestic chicken; and 33.1 percent all other sources.

Imported pork and domestic chicken
The largest gross exposure was related to imported pork with a wide selection of 28 subtypes and the highest number of unique subtypes, 16, detected in this product. However, its share from the number of disease cases was estimated to be only the third largest — an eight‐year average 10.5 percent — because of the differences in subtype distributions between humans and imported pork. In the data set, three of 16 subtypes unique to imported pork represented zero counts in the human data set from 2008 to 2015.

The smallest proportion of disease cases was attributed to domestic chicken meat with an eight‐year average of 2 percent. Only six Salmonella subtypes were detected in this source over the eight‐year period, and these subtypes, excluding Salmonella Infantis, were not particularly common in humans.

The effect of Salmonella outbreaks on source attribution results was examined by including outbreak‐related cases in the data set. Results hardly changed because the number of outbreaks was relatively low at around one per year and some were relatively small.

“The major challenge ahead is extending the model so that more accurate laboratory methods, such as genotyping results, can also be used in connecting infections,” said Jukka Ranta, a research professor from the Finnish Food Authority.

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