Raw pork was the suspected vehicle in an outbreak with 203 cases of Salmonella Muenchen in the German federal state of Saxony between 25 June and 7 August in 2013.
In 2014, there was an outbreak with 247 cases caused by the same serovar affecting Saxony, Brandenburg, Saxony-Anhalt and Thuringia in the eastern part of the country.
European regulations do not make provisions for Salmonella control measures on pig farms involved in human disease outbreaks, said the researchers.
“To our knowledge, all relevant regulations and laws were followed in the aftermath of the outbreak in 2013. Yet, only one year later the same strain caused another even larger outbreak, including at least one death, showing that the multi-barrier approach to prevent human Salmonella infections failed.”
In poultry, measures must be taken when presence of certain Salmonella serovars is suspected.
Of all cases, 30 were hospitalised after symptom onset and four died (all female, age 81-93 years). For one patient, salmonellosis was reported as cause of death; for the other three, deaths were attributed to causes other than salmonellosis but without further information.
Raw pork implicated
Evidence from epidemiological, microbiological and trace-back implicated different raw pork.
S. Muenchen was detected in two samples from routine testing. These were different products like minced pork for raw consumption and a raw pork sausage called ‘Knacker’, also to be consumed raw. Another specimen of brine used for meat preparations tested positive.
None of 227 surface swabs taken in kitchens of nursing homes, butcher shops and slaughterhouses tested positive.
Traceback analysis of S. Muenchen-contaminated raw pork sausages narrowed the possible source to 54 pig farms and S. Muenchen was detected in three, which traded animals with each other.
One of the farms had been the suspected source of the 2013 outbreak.
Meat processors and slaughterhouses visited, sampled and investigated for Salmonella tested negative.
S. Muenchen isolates from stool of patients in 2013 and 2014 as well as food and environmental surface swabs of the three pig farms shared indistinguishable pulsed-field gel electrophoresis (PFGE) patterns.
The researchers identified weaknesses from an infection control point of view when reviewing provisions to control Salmonella in pigs.
“Most notably, competent authorities, such as veterinary control services, have no legal mandate to initiate measures at farms even if they can be linked to human cases. Yet, they should be able to demand mandatory preventive measures at primary production after a foodborne outbreak.
“Legislators should review the existing regulatory framework regarding protection of the consumer against Salmonella in raw pork products with a focus on primary production to critically assess where regulations can be tightened to better prevent future outbreaks and to protect the consumer from infectious diseases.”
Measures to stop the 2013 outbreak were applied at meat processing level addressing severe hygienic deficiencies.
Local health authorities attempted to interview all adult notified cases (18 years and older) with reported salmonellosis starting from 26 May 2014 using a questionnaire.
It asked about consumption of pork as well as points of purchase e.g. butcher shops and restaurants.
The aim of interviews, until 14 July 2014, was to identify common points of purchase (at least two) to provide possible starting points for trace-back investigations along the production chain.
Of 148 patients, 80% (119) ate pork products in the three days before symptom onset and 85% had raw pork consumption.
In total, 11 common points of purchase were identified (mainly supermarkets and butcher shops).
Researchers did a cohort study among staff of a nursing home with cases among staff and residents, in which raw pork sausages from unopened packages had tested positive for S. Muenchen ‘Braunschweiger’ and ‘Schinken-Teewurst’.
A total of 27 of 64 staff members of the nursing home completed the online questionnaire and six were defined as cases.
“Raw pork remains a risky, yet frequently consumed food product in Germany that may cause salmonellosis and other infectious diseases, e.g. yersiniosis,” said researchers.
“Recommendations, e.g. not to serve raw pork(-products) to vulnerable populations, are necessary building blocks of foodborne illness prevention strategies, but are apparently not sufficient to prevent salmonellosis outbreaks caused by pork in Germany.”
“Two consecutive large outbreaks of Salmonella Muenchen linked to pig farming in Germany, 2013 to 2014: Is something missing in our regulatory framework?”
Authors: A Schielke, W Rabsch, R Prager, S Simon, A Fruth, R Helling, M Schnabel, C Siffczyk, S Wieczorek, S Schroeder, B Ahrens, H Oppermann, S Pfeiffer, SS Merbecks, B Rosner, C Frank, AA Weiser, P Luber, A Gilsdorf, K Stark, D Werber