Daily flags from potential Children's Hospital surveillance systems (black symbols) vs. all other hospitals (red symbols) plotted along with CDC sentinel physician data for winter 2004. The smoothed number of cases is shown in the solid (unspecified infection) and dotted lines (respiratory complaints) and color-coded by hospital. The flagging of the detection algorithms is represented by black (for CNMC) and red (all other hospitals) symbols (+ for unspecified infection, o for respiratory, and Δ for MV unspecified infection and respiratory). The percentage of cases seen by sentinel physicians each week who have ILI is plotted on the right-hand vertical axis. The vertical line corresponds to the first date on which the sentinel physician data exceeds 2.5%, the CDC threshold on the national level for declaring the flu season.