E. coli, the organism responsible for the fast-food-hamburger outbreak, is a common family of bacteria. E. coli is a normal inhabitant of the large intestines. We're not poisoned by our own E. coli because it's a more benign strain. But even this relatively common strain can become a pathogen.

The type of E. coli responsible for the recent outbreak is different. Called 0157:H7 since its discovery in 1982, this uncommon bug is a dangerous and virulent strain of E. coli. It was believed to have gotten into the meat when cattle containing this rare strain were used to make ground beef.

Even though this virulent strain was in the meat, if the meat had been cooked properly (up to 155 degrees), the E. coli would have been destroyed. At this temperature, the meat is steaming hot and gray in appearance and the juices run clear.