Number of cases of influenza-like illness presenting to sentinel providers and reported to the Centers for Disease Control and Prevention. Number of visits of influenza-like illness (ILI) reported by the United States. Outpatient Influenza-Like Illness Surveillance Network (ILINet) National Summary 2008 to 2009, by age. Source: http://www.cdc.gov/flu/weekly/weeklyarchives2009-2010/data/senAllregt46.htm.⁴