My regular readers know I have a bit of an obsession with food-borne illness. Why? Because it’s such a difficult and old problem. (Obviously germs have been contaminating food and sickening animals long before people were around.) Modern sanitation and farming have made our food much safer, but occasional outbreaks remind us that our current methods are still imperfect. This week an outbreak of the bacterium Listeria has sickened over 20 people in seven states. (California has not been affected...