Disentangling outbreaks using whole-genome sequencing: concurrent multistate-outbreaks of Salmonella Kottbus in Germany, 2017.

In June 2017, an outbreak of Salmonella Kottbus infection was suspected in Germany. We investigated the outbreak with whole-genome sequencing (WGS) and a case-control study. Forty-six isolates from 69 cases were subtyped. Three WGS clusters were identified: cluster 1 (n = 36), cluster 2 (n = 5) and cluster 3 (n = 3). Compared to controls, cluster 1 cases more frequently consumed raw smoked ham (odds ratio (OR) 10, 95% confidence interval (CI) 1.2-88) bought at supermarket chain X (OR 36, 95% CI 4-356; 9/10 consumed ham Y). All four cluster 2 cases interviewed had consumed quail eggs. Timely WGS was invaluable in distinguishing concurrent outbreaks of a rare Salmonella serotype.