Outbreak of Salmonella Newport linked to imported frozen cooked crayfish in dill brine, Sweden, July to November 2019

In the autumn of 2019, the Public Health Agency of Sweden identified a cluster of Salmonella Newport cases by whole genome sequencing (WGS). Cases' distribution in place and time indicated a nation-wide ongoing outbreak. An investigation was initiated to identify the source and prevent further cases. We conducted a case–case study based on notified salmonellosis cases and a Salmonella trawling questionnaire, comparing food exposures between 20 outbreak cases and 139 control cases. Exposures were compared by adjusted odds ratios (aOR) with 95% confidence interval (CI) using logistic regression. Implicated foods were sampled. Outbreak cases were more likely to have consumed crayfish (aOR?=?26; 95% CI: 6.3–105) and one specific brand of imported frozen, pre-cooked whole crayfish in dill brine was identified as the source. The retail company recalled all remaining packages. Salmonella Newport was detected in different batches from retail and in one sample from border control. Isolates from food samples clustered with the human outbreak strain by WGS. This investigation demonstrated the successful use of a case–case study and targeted microbiological testing to identify the source of the outbreak. The immediate action taken by the retail company was important to confirm the source and prevented further cases.