In 1981, the U.S. Centers for Disease Control and Prevention (CDC) began collecting reports of influenza outbreaks from state and territorial epidemiologists.

National data on influenza activity for the 1981-1982 season were obtained from three major sources: 1) weekly reports of mortality from 121 cities, including the ratio of pneumonia and influenza deaths to total deaths, an index of the relative mortality attributable to influenza; (2) weekly reports of the number of respiratory specimens tested and the number and types of influenza isolates identified by 63 collaborating state, county, city, or military laboratories; and (3) weekly semi-quantitative estimates from each state health department of the extent of influenza-like morbidity indicated by their individual statewide surveillance systems. In addition, spontaneous reports of unusual cases and outbreaks of influenza were received by CDC.

Today, Influenza Division at the CDC collects, compiles and analyzes information on influenza activity year-round in the U.S.