Figure 4. Multivariate cumulative sum (CUSUM) algorithm flags for two different syndromic surveillance systems for 2005–2006, one based on three streams of chief complaint data (flags denoted by circles) and one based on three streams of emergency department diagnosis data (flags denoted by triangles). The CDC regional influenza like illness (ILI) curve is plotted in the center of the graph for reference. The gray and black lines at the bottom of the graph denote observed daily counts for the complaint and diagnosis data, respectively.