Recent research by the American Society for Microbiology has tried to explain why salads containing lettuce and spinach are subject to colonisation by Salmonella, E. coli and Listeria.

In 2014, food poisoning bacteria were found in beansprouts in the US, infecting over 100 people, a quarter of whom had to be hospitalised. Earlier this year, salmonellosis hit more than 50 people in Victoria, Australia, who had eaten salad leaves, and in July, for the same reason, 161 UK people fell ill and two people died.

Even though the study doesn’t show any increased risk to eating bagged salads, it highlights the need for continued good practice in both production and consumption, giving instructions as to how to store, prepare and use them. Salad containers that look swollen, for example, should be avoided. To minimise risks, consumers need to store the salad in the fridge and use it as quickly as possible after purchase.