The culprit in the deadly outbreak in Europe is a rare strain of the E. coli bacteria.
There are hundreds of kinds of E. coli, or Escherichia coli. It's a common and mostly harmless bacteria found in the gut of warm-blooded animals, including humans.
But some — like the O104:H4 strain identified in Europe — produce a toxin and can make people sick.
Contaminated foods or liquids can cause severe stomach cramps and diarrhea, which is often bloody, and vomiting. Most people recover within a week. Some — especially young children and the elderly — may develop a serious complication that can result in kidney failure, requiring dialysis and transfusions.
Officials have not yet pinpointed the European source, but other outbreaks have been traced to undercooked or raw hamburger, salami, spinach, lettuce, sprouts and unpasteurized milk and juices.
Infected animals can spread the bacteria through their feces. The main source of illness for humans is cattle. E. coli from cattle can get into ground beef during processing and cattle runoff can contaminate fields. It can end up in water when human or animal waste is washed into rivers, lakes or ground water.
E. coli can also be spread from person to person.
To prevent infections, wash your hands after changing diapers or using the bathroom and before preparing or eating food. Cook meats thoroughly and avoid unpasteurized milk or juices.