A report commissioned by the Food Standards Agency has said pre-packed sandwiches have been responsible for the majority of listeria outbreaks in hospitals since 2003.

Food safety company STS, which undertook the report, said hospital staff were putting patients’ lives at risk by giving them the contaminated sandwiches. Listeria can trigger meningitis and kills up to 30% of those infected.

Pre-packed sandwiches often contain protein-rich fillings, which listeria thrives on. The company said there was a concern that preparation was not always thorough, giving listeria time to multiply.

STS director of food safety Fiona Sinclair told The Daily Mail: “Hospitals and care homes feed the most vulnerable people in society. The last thing these people need is to get something else on top of their illness.”

The firm’s report has prompted the FSA to revise its guidance to hospitals and care homes on minimising the risk of listeria.

In August 2014, the NHS was criticised for its junk food after an investigation revealed hospitals house dozens of fast food restaurants and coffee shops.