As an example, we analyzed fever syndrome data from 1 ED. The mean count was 4.9 per day, and the 99th percentile threshold values were 3.86 SDs for the initial and 3.55 for the best algorithm. Over 632 days, the sensitivity for detecting 8 additional counts was 47.2% for the initial and 70.9% for the best algorithm (23.7% difference). Data for a 2-month period showed that the calculated SD (Figure 3 , panel A) and the threshold value (i.e., count needed to trigger an alert; Figure 3 , panel B) varied substantially for the initial algorithm but were comparatively stable for the best algorithm. During the 2-month period, 8 additional counts would be detected by initial and best algorithms on 30 days, by only the initial algorithm on 2 days, and by only the best algorithm on 19 days; neither algorithm detected the additional counts on 10 days (Figure 3 , panel C).