The vaccination of commercial hens against common salmonella strains, which began in the mid-1990s in the UK, has been a “major public health success” and has “substantially reduced egg-associated salmonella infections,” according to Dr Charlotte Hammer at the University of Cambridge.

Another quality control measure is the British Lion Scheme, launched in 1998.

Any suppliers of eggs given the British Lion mark have to stick to a strict code that covers the vaccinating of hens, regular testing and a passport system to make sure hens are traceable.

Paul Wigley, professor in animal microbial ecosystems at the Bristol Veterinary School, says improved surveillance and detection has also helped.

“However, we do still import a large number of eggs and egg product, and salmonella could be contained within these because the countries in which they’re produced don’t use that same level of control,” he added.

Meanwhile, Mark Williams, chairman of the British Egg Industry Council, said food businesses which import eggs should check their supply lines for vaccination information and that all the food safety checks have been done.