What to know about E. coli and the McDonald's outbreak

A food poisoning outbreak tied to McDonald’s Quarter Pounders was caused by a common type of E. coli bacteria that can cause serious illness and death.

Particularly vulnerable are young children, older people or those with weakened immune systems.

About 50 people have fallen ill in the McDonald's outbreak, and one has died, with ages ranging from 13 to 88, according to the Centers for Disease Control and Prevention.

A preliminary investigation suggests raw slivered onions served on Quarter Pounders are a likely source of the outbreak.