Outbreak of Listeria monocytogenes in an oncology unit associated with sandwiches consumed in hospital.

In May 2003, two adult patients in an oncology unit were diagnosed with listeriosis, and sandwiches consumed in the hospital were identified as a common risk factor. Both patients were infected by the same strain of Listeria monocytogenes. Sandwiches collected from the hospital and external sandwich producer, as well as sites within the manufacturing environment, were contaminated by the same strain of L. monocytogenes. Sandwiches consumed in other hospitals have been associated with small clusters of listeriosis patients in the UK. This report describes the investigations following diagnosis of the two infections, and highlights a more general problem with sandwiches sold in hospitals.