Visits for influenza-like-illness reported by sentinel providers for different age groups, during the 2009 (H1N1) pandemic influenza period and recent seasonal influenza periods, in the United States of America.^*

Abbreviations: y: years, wks: weeks. * Data are from US Centers for Disease Control and Prevention; US Outpatient Influenza-like Illness Surveillance Network (ILINet) (http://www.cdc.gov/flu/weekly/fluactivity.htm).