Time course of faecal excretion of VTEC O157:H7, strain CCUG 53931, in experimentally inoculated calves. Excretion is shown for calves I, II and III in stall A (upper panel) and for calves IV, V and VI in stall B (lower panel). Calf I was left un-inoculated. Calf VI was inoculated for the first time on day 42. On that same day, calf V was re-inoculated. Samples negative on counting but culture-positive on IMS are denoted as IMS positive (grey bar), while samples culture-negative on IMS are denoted as IMS negative. The calves were euthanised after the last shown result of sampling.