What is the primary source of staphylococcal food poisoning, and how can this disease be prevented?

Primary source is humans and prevention includes proper hand washing and proper cooling of potentially hazardous foods.

It is this heat-stable toxin that causes the symptoms of the illness. The heat stable toxin, once produced in food, cannot be destroyed by reheating or cooking.
-Foods on which this organism commonly grows include: sandwiches, lunchmeat, salami, cooked ham, salad dressings, pastries and custards.