Microbiological safety of sandwiches from hospitals and other health care establishments in the United Kingdom with a focus on Listeria monocytogenes and other Listeria species

In the United Kingdom between 1999 and 2004, there were four outbreaks of Listeria monocytogenes infection associated with sandwiches purchased from or provided in hospitals. Elderly or immunocompromised individuals and pregnant women are particularly vulnerable to infection; therefore, the focus of this study was on sandwiches served in health care establishments. Of 3,249 sandwich samples collected between April 2005 and March 2006, 3.3% were of unsatisfactory microbiological quality because of high levels of Enterobacteriaceae (2.0%; > or = 10(4) CFU/g for sandwiches not containing salad), Escherichia coli (0.8%; > or = 10(2) CFU/g), Staphylococcus aureus (0.6%; > or = 10(2) CFU/g), and/or Listeria spp. (0.1%; two samples with L. welshimeri at 1.8 x 10(2) and 7.4 x 10(3) CFU/g and one sample with L. seeligeri at 1.8 x 10(3) CFU/g). Overall, 7.6% of sandwiches were contaminated with Listeria spp. L. monocytogenes was detected in 2.7% (88) of samples: 87 samples at < 10 CFU/g and 1 sample at 20 CFU/g. More frequent contamination with Listeria spp. and L. monocytogenes was found in sandwiches collected from hospital cafeterias, shops, or wards and in sandwiches stored and/or displayed at temperatures higher than 8 degrees C. The presence of Listeria spp. and L. monocytogenes also was associated with sandwiches that (i) were supplied from outside the establishment, (ii) were prepacked, (iii) had a main sandwich filling of poultry meat, or (iv) contained salad ingredients, soft cheese, and/or mayonnaise. Control of L. monocytogenes in sandwich manufacturing and within health care establishments is essential to minimize the potential for consumption of this bacterium at levels hazardous to health. The findings from this study support the proposal that manufacturers supplying sandwiches to health care establishments should follow the British Sandwich Association recommended guidelines of complete absence of L. monocytogenes in sandwiches at the point of production.