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

abcnews.go.com:

A food poisoning outbreak tied to McDonald’s Quarter Pounders was caused by a common type of E

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.

Here's what to know about the dangerous germ:

E. coli is a type of bacteria found in the environment, including water, food and in the intestines of people and animals. There are many kinds of harmless E. coli, but a few types can make people seriously ill. The McDonald's outbreak is caused by E. coli O157:H7, which produces a toxin that causes dangerous diarrhea and can lead to kidney failure and other serious problems, according to the CDC.

People can get sick from E. coli poisoning when they consume contaminated foods or through contact with animals, the environment or other people who are infected. Health officials initially focused on fresh slivered onions and beef patties as the possible sources of the McDonald's outbreak. But the beef patties are an unlikely source because of federal requirements for testing meat and McDonald’s protocols that call for cooking it to a temperature that kills the bacteria. The onions are served raw.

Symptoms occur quickly, within a day or two of eating contaminated food, and typically include fever, vomiting, diarrhea or bloody diarrhea and signs of