In 2019, four outbreaks of listeriosis were investigated. For two of them, the source of infection remained unknown. One outbreak involving five people, from 2018–2019, was linked to Romanian pork products.

The other outbreak involved prepacked sandwiches served National Health Service (NHS) hospitals. After two patients were infected with Listeria monocytogenes in the same hospital, and one subsequently died, the outbreak was detected in North West England. Whole-genome sequencing (WGS) was used to identify other cases across seven NHS Trusts.

Between May 16–June 14, 2019, nine confirmed cases associated with the outbreak were identified, and seven people died. All nine of the people had previously received care at hospitals supplied by The Good Food Chain, the manufacturer of the sandwiches. It was confirmed that eight of these people had consumed the prepacked sandwiches. 

The outbreak strain involved Listeria monocytogenes isolates from chicken sandwiches. Cooked chicken samples supplied by the sandwich manufacturer and a meat producer named North Country Cooked Meat were confirmed as the outbreak stain, by WGS analysis.