Leukocyte count to consider severity of the CDI: Any white blood cell count (WBC) measured between two days before and two days following the date of the stool sample. If a patient had WBC measured on the date of the stool sample then this was selected. If they did not have WBC measured on the date of the stool sample but had WBC measured between one day before and one day following their stool sample, then this was selected. If they did not have WBC measured between one day before and one day following their stool sample but had WBC measured between two days before and two days following their stool sample, then this was selected. If they did not have WBC measured on the date of the stool sample but had WBC measured both one day before and one day following the date of stool sample, or had WBC measured both two days before and two days after the stool sample but not between these measurements, then the highest of the two measurements was selected.