An outbreak of monophasic Salmonella Typhimurium associated with raw pork sausage and other pork products, Denmark 2018-19.

I G Helmuth,E Litrup,T Jensen,L Espenhain,L Müller,J Kjeldgaard,S Schjørring,S Ethelberg

doi:10.1017/s0950268819002073

Abstract

In Denmark, outbreaks of salmonella with more than 20 cases have become rare. In November 2018, an outbreak of monophasic Salmonella Typhimurium was detected and an investigation initiated with the aim of identifying the source and controlling the outbreak. Outbreak cases were defined based on core genome multilocus sequence types. We conducted hypothesis-generating interviews, a matched case-control study, food sampling and trace-back investigations. We identified 49 cases distributed across Denmark. In univariable analyses a traditional form of raw Danish pork sausage (medister sausage), pork chops and ground veal/pork showed matched odds ratio of 26 (95% CI 3-207), 4 (95% CI 1-13) and 4 (95% CI 1-10), respectively. In a multivariable analysis, only medister sausage remained significant. Several patients described tasting or eating the sausage raw or undercooked. Samples of medister sausage analysed were negative for salmonella and investigations at the production site did not reveal the mechanism of contamination. In conclusion, in spite of having eliminated salmonella in the egg and broiler industry, Denmark is still at risk of major salmonella outbreaks. We identified a raw pork sausage as a particular risk product that needs to be thoroughly cooked before consumption. Tasting raw meat or eating undercooked pork should be discouraged.

Highlights

In Denmark, the endemic level of salmonellosis has been markedly reduced over the last two decades
Genetic clusters are initially defined by Serum Institut (SSI) and the investigation of national outbreaks is coordinated by the Central Outbreak Management Group with participation from SSI, the Danish Veterinary and Food Administration (DVFA) and the National Food Institute at the Technical University of Denmark (DTU-FOOD) [1]
In order to examine the efficiency of the outbreak investigation, we described the time between events of the investigation

Summary

Introduction

In Denmark, the endemic level of salmonellosis has been markedly reduced over the last two decades. Salmonella Typhimurium does, still exist in Danish pigs and pork where it has the potential to cause outbreaks, large national foodborne outbreaks with more than 20 cases have become increasingly rare in recent years [1, 5,6,7]. Since 2017, all isolates from the national surveillance of salmonella in animals, food and humans have been whole genome sequenced (WGS) as part of the surveillance programme. Human cases of salmonellosis are laboratory notifiable and isolates are analysed by WGS at the Statens Serum Institut (SSI). Genetic clusters are initially defined by SSI and the investigation of national outbreaks is coordinated by the Central Outbreak Management Group with participation from SSI, the Danish Veterinary and Food Administration (DVFA) and the National Food Institute at the Technical University of Denmark (DTU-FOOD) [1]

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