Figure 4.

Comparison of Centers for Disease Control and Prevention (CDC) influenza-like illness (ILI) surveillance data with prospective sample collection dates. A, Percentage of visits for ILI reported by the US Outpatient ILI surveillance Network (ILINet), weekly national summary, 30 September 2007 to 30 July 2011. Figure from the CDC website at http://www.cdc.gov/flu/weekly/weeklyarchives2010–2011/picILI30.htm, accessed 20 September 2011. B, The number of samples collected at Blood Systems, Inc (BSI) sites (early 2008) or American Red Cross (ARC) sites (late 2008 through late 2010). The peaks in sample collection for both organizations corresponded to reported high levels of ILI activity in the community (panel A).