Comparison of positive frequencies estimated by the stamp method in hospital environments. (Left panels) Positive frequencies and relative fold change values estimated by the stamp method. Color changes show the degree of the stamp value, ranging from highest contamination (red) to lowest contamination (yellow). The numbers in each of the squares show fold change values. “A” hospital, >500 beds with the following sampling period, October 2011 to December 2011. “B” hospital, 100–500 beds with the following sampling period, December 2011 to February 2012. “C” hospital, <100 beds with the following sampling period, November 2011 to December 2011. N1–3 or 4, nurse areas. P1–8, patient areas. OG, Department of Obstetrics and Gynecology. S, Department of Surgery. IM, Department of Internal Medicine. Arrows indicate the order of the sampling times. (Middle panels) Distribution of positive frequencies in each unit of each hospital. Five categories were provided (20 ≤ value, 10 ≤ value < 20, 5 ≤ value < 10, 1 ≤ value < 5, and <1-fold). (Right panels) Comparison of nurse and patient areas with the stamp method. The data show the relative fold change over the detection limit of the stamp method. *p < 0.05 (Student’s t-test).