TABLE 3. Examples of possible nonpharmaceutical intervention surveillance indicators for an influenza pandemic.

Key influenza indicator	U.S. data source	Measure of influenza activity
Indicators of spread or level of influenza activity
Percentage of patient visits to health care providers for ILI in the United States	Outpatient ILI Surveillance Network (ILINet), which includes approximately 2,900 enrolled outpatient health care providers in 50 states	Current ILI level in relation to most recent national and region-specific baseline levels, with CDC providing baseline values for the 10 HHS surveillance regions and for the United States as a whole https://www.cdc.gov/flu/weekly/overview.htm
ILI activity by state: percentage of outpatient visits for ILI in a state (ranges from minimal to high)	Outpatient ILI Surveillance Network (ILINet) Additional: Flu Near You https://flunearyou.org/	Ten activity levels that compare the mean reported percent of visits due to ILI for the current week to noninfluenza weeks, specifying the number of standard deviations at or above the mean for the current week https://www.cdc.gov/flu/weekly/FluViewInteractive.htm
Geographic spread of influenza in a state (ranges from none to widespread)	State and Territorial Epidemiologists reports	Estimated weekly levels of geographic spread (local, regional, or widespread) of influenza activity reported by state health departments https://www.cdc.gov/flu/weekly/overview.htm
Percentage of respiratory specimens that test positive for influenza viruses in the United States	Approximately 110 U.S. WHO collaborating laboratories and 240 National Respiratory and Enteric Virus Surveillance System laboratories	National and regional percentage of respiratory specimens testing positive for influenza viruses https://www.cdc.gov/flu/weekly/FluViewInteractive.htm
Absenteeism rates due to ILI in child care facilities, K–12 schools, or colleges and universities (reflects number of ILI cases)	ILI monitoring/surveillance systems in child care facilities, K–12 schools, or colleges and universities	Increased absenteeism rates due to ILI in child care facilities, K-12 schools, or colleges and universities (reflects increased number of ILI cases)
Laboratory-confirmed influenza cases among students, teachers, and staff members		Increases in laboratory-confirmed influenza cases among students, teachers, and staff members
		Laboratory-confirmed outbreaks of influenza in child care facilities, K–12 schools, or colleges and universities
Indicators of clinical severity of influenza
Influenza-associated hospitalizations	Influenza Hospitalization Surveillance Network (FluSurv-NET), which collects data from the 10 Emerging Infections Program sites, as well as Michigan, Ohio, and Utah (https://wwwnc.cdc.gov/eid/article/21/9/14-1912_article)	Population-based rate of influenza-associated hospitalizations in multiple geographic areas https://www.cdc.gov/flu/weekly/FluViewInteractive.htm
Percentage of deaths attributed to pneumonia and influenza	National Center for Health Statistics mortality surveillance system	The percentage of death certificates indicating pneumonia and influenza compared with a seasonal baseline and epidemic threshold value calculated for each week (using a periodic regression model) https://www.cdc.gov/flu/weekly
Influenza-associated deaths among persons aged <18 yrs	Influenza-Associated Pediatric Mortality Surveillance System	Any laboratory-confirmed influenza-associated deaths in children, all of which are reported through this system https://www.cdc.gov/flu/weekly/FluViewInteractive.htm

Abbreviations: HHS = U.S. Department of Health and Human Services; ILI = influenza-like illness; WHO = World Health Organization.