Per the EPA, 78% of outbreaks and 95% of diseases caused by distributions systems resulted from an in-appropriately controlled cross-connection. (Source: Ed Bettinger, 2007 C.C.C. Conference)
Between 1920 and 1980, over 60,000 cases of disease resulted from backflow occurrence (Ed Bettinger)
From 1981 to 1998, the CDC documented 57 water borne disease outbreaks related to cross-connections and resulting in 9,734 illnesses.
On average, a backflow prevention assembly fails the annual inspection test every 5 years.