A century ago, autoimmune diseases were virtually unheard of. In the rare instance that one did occur, it was among the wealthy who bathed frequently and had proper sewage disposal. The average person back then was exposed to a large quantity and wide variety of germs throughout their lifetimes, by drinking impure water, eating food that was near spoiled or contaminated, and living in close proximity to livestock without a sewage system. Infectious diseases caused a third of all deaths.