We all have Escherichia coli bacteria in our intestines. These are the good strains of the bacteria. They help us digest our food. There are billions of these bacteria in our intestines and in our feces. Of the hundreds of strains of good E. coli, there are only a few strains that are bad for us. These strains usually cause stomach problems and diarrhea.

The worst of these strains is labeled E. coli 0157. This strain is common in healthy cows, sheep, and goats. But when it gets into humans, it causes illness. This strain can kill humans, but only rarely. It kills our red blood cells and causes our kidneys to stop functioning. Hospitalization and transfusions are necessary to prevent death.

Most people just get mildly sick from E. coli 0157. There are usually just two symptoms: stomach cramps and diarrhea (non-bloody or bloody). These symptoms may last up to two weeks. The very young and the very old are most susceptible to severe symptoms. In the US, more than 100,000 people get infected annually. People who live in countries with contaminated water develop immunity to infection.

The primary sources of infection are contaminated water, undercooked hamburger, unwashed fruits and vegetables, and unpasteurized milk or milk products. Swimming in or swallowing contaminated lake water can also result in infection. In the US, outbreaks involving hundreds of people have been traced to undercooked hamburgers at fast food restaurants, to packaged vegetable products such as spinach, and even to petting zoos. One of the best preventive measures is to wash our hands often, and wash thoroughly after using the toilet.