Weekly case numbers were obtained from CDESS and counted patients with Shigella who had diagnosis or specimen collection dated between January 1, 2006, and December 31, 2010. Six statistical models were applied to the weekly case numbers in generating signals to identify outbreaks, and signals were compared to the actual outbreak to evaluate their detection powers. Outbreak-related cases from CDESS were removed for the modeling purpose except for the cumulative sum-related methods, which used all cases. The sensitivity (SE), specificity (SP), positive predictive value (PPV) and negative predictive value (NPV) were calculated to evaluate the performance of each method.