Listeria really is a different risk in its own category. You really need to read up on it to put it in context.

When Mum had me it was in the mid 1970's.

Just in the time I've been an adult, eating out has changed in that time, particularly regarding salads, there's a proliferation of side salads everywhere you eat out these days. The problem with Listeria is it isn't killed by refrigeration, only by heat.