some diseases now known to be viral were recorded as foodborne before the nature of viruses was understood. In particular, outbreaks of poliomyelitis associated with drinking raw milk were recorded before the poliomyelitis viruses (polioviruses) had been isolated. Polioviruses only infect humans and other primates and are shed in feces. The problem of milk transmission of polioviruses, therefore, was a clear example of food handler–associated transmission, which was solved by improved sanitation and almost universal pasteurization of milk before vaccines became available and eradicated poliomyelitis in the developed world.