and husbandry best practices with regard to manure storage and use, and that though the E. coli contamination had almost certainly come from the farm's manure usage, the farm's operator was not at fault for contamination of the well. Outbreak Beginning May 17, 2000, absenteeism in the Walkerton school system took an upswing. That day, the Walkerton Hospital treated seven children suffering from gastrointestinal ailments involving cramping and diarrhea. The illnesses were not initially recognized as part of a pattern, and no report was made to the Bruce-Grey-Owen-Sound Health Unit, which was responsible for public health in Grey and Bruce counties. On May 18, twenty students were absent from the Mother Teresa School in Walkerton; the next day, twenty-five were, with a further four sent home from Mother Teresa and eight sent home from the Walkerton Public School. The increasing number of community illnesses became even more noticeable on May 19, when a pediatrician and a retirement home both reported outbreaks of gastroenteritis among their charges. By May 20, the Walkerton hospital had fielded calls from more than a hundred people about incidents of gastroenteritis in the town, and attended to dozens more in their Emergency Department. Attending physicians and health care workers, aware that the gastroenteritis symptoms they were seeing were consistent with possible E. coli infection, began collecting stool samples from affected patients. When public health officials put together common reports, they found that three area hospitals had recorded incidents of patients suffering from gastroenteritis symptoms. Walkerton's hospital recorded the highest number of such patients, with at least twenty patients visiting the emergency department with bloody diarrhea on May 20, and two more patients admitted for diarrhea-connected dehydration. Hospitals in two neighbouring towns had each seen one case of bloody diarrhea. Initial public health response On May 20, early laboratory testing was completed on fecal samples submitted the day before. E. coli O157 was found in at least one sample from the Owen Sound Hospital; when health officials contacted other hospitals in the Bruce-Grey system, they found that all were handling patients with gastrointestinal ailments consistent with E. coli infection. Potential E. coli infection changed the treatment plan for patients reporting to these hospitals or to local doctors; anti-motility medication that would typically be prescribed to patients suffering from diarrhea unrelated to E. coli could in fact exacerbate the condition of patients whose diarrhea was due to E.