Whole genone sequencing fingers ham as source of Salmonella outbreak in Netherlands

In January 2017, an increase in reported Salmonella enterica serotype Bovismorbificans cases in the Netherlands was observed since October 2016. We implemented a case–control study to identify the source, including all cases after December 2016.

Adjusted odds ratios were calculated using logistic regression analysis. We traced back the distribution chain of suspected food items and sampled them for microbiological analysis. Human and food isolates were sequenced using whole genome sequencing (WGS).

From October 2016 to March 2017, 54 S. Bovismorbificans cases were identified. Sequencing indicated that all were infected with identical strains. Twenty-four cases and 37 controls participated in the study. Cases were more likely to have consumed ham products than controls (aOR = 13; 95% CI: 2.0–77) and to have shopped at a supermarket chain (aOR = 7; 95% CI: 1.3–38).

Trace-back investigations led to a Belgian meat processor: one retail ham sample originating from this processor tested positive for S. Bovismorbificans and matched the outbreak strain by WGS. All ham products related to the same batch were removed from the market to prevent further cases. This investigation illustrates the importance of laboratory surveillance for all Salmonella serotypes and the usefulness of WGS in an outbreak investigation.

Outbreak of Salmonella Bovismorbificans associated with the consumption of uncooked ham products, the Netherlands, 2016 to 2017

Eurosurveillance; Volume 23; Issue 1; 4 January 2018

Brandwagt Diederik, van den Wijngaard Cees, Tulen Anna Dolores, Mulder Annemieke Christine, Hofhuis Agnetha, Jacobs Rianne, Heck Max, Verbruggen Anjo, van den Kerkhof Hans, Slegers-Fitz-James Ife, Mughini-Gras Lapo, Franz Eelco