E. coli O157:H7 did not burst onto the scene in the early 1990s, as many in the big food business like to think. It slowly crept into our food supply, spreading in the enormous feedlots that began to dot the U.S. landscape during the last century. The bacteria is now endemic and can be found in cows, sheep, and wild animals such as boar, elk, and deer. As few as fifty E. coli O157:H7 bacteria are enough to cause human illness—and as many as 100,000 can fit on the head of a pin.

Once this strain of E. coli makes it into our small intestine, it can damage the intestinal wall, causing severe cramping and bloody diarrhea. In some instances, the toxin that the bacteria releases gets into the bloodstream, damaging red blood cells and causing severe complications like kidney failure, stroke, brain damage, and death.

via A History of Hamburger E. Coli Outbreaks | Lucky Peach.