In early 1982, approximately 47 healthy adults and children living in Oregon and Michigan developed a severe illness with symptoms of stomach pain and cramping followed by episodes of bloody diarrhea.1 At first, the cause of this disease was a mystery because all the routine laboratory tests were negative for the known causes of diarrheal illnesses. As a result, no one knew how to treat the sick patients. The culprit, a type of bacteria called Escherichia coli O157:H7—was ultimately found to be responsible for the outbreak of severe diarrhea. This finding was quite a surprise to health-care professionals, because E. coli (the name Escherichia coli is often shortened to E. coli for ease of reference) bacteria are very common and generally exist in people’s bodies without causing disease. In addition, this newly identified type (O157:H7) was rare and had previously been implicated in only one other case of bloody diarrhea, back in 1975.2 The next step was to determine how these patients had acquired such a new and rare infection. A tedious and costly investigation was required to answer this question.