* This summary includes data reported as of June 24, 2006.  Reporting is incomplete and numbers may change as more reports are received.
§ Surveillance Regions: New England (Connecticut, Maine, Massachusetts, New Hampshire, Vermont, Rhode Island); Mid-Atlantic (New Jersey, New York City, Pennsylvania, Upstate New York); East North Central (Illinois, Indiana, Michigan, Ohio, Wisconsin); West North Central (Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, South Dakota); South Atlantic (Delaware, Florida, Georgia, Maryland, North Carolina, South Carolina, Virginia, Washington, D.C., West Virginia); East South Central (Alabama, Kentucky, Mississippi, Tennessee); West South Central (Arkansas, Louisiana, Oklahoma, Texas); Mountain (Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah, Wyoming); Pacific (Alaska, California, Hawaii, Oregon, Washington).
¥The number and/or proportion of an influenza virus type/subtype may differ betwee* This summary includes data reported as of June 24, 2006.  Reporting is incomplete and numbers may change as more reports are received.
§ Surveillance Regions: New England (Connecticut, Maine, Massachusetts, New Hampshire, Vermont, Rhode Island); Mid-Atlantic (New Jersey, New York City, Pennsylvania, Upstate New York); East North Central (Illinois, Indiana, Michigan, Ohio, Wisconsin); West North Central (Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, South Dakota); South Atlantic (Delaware, Florida, Georgia, Maryland, North Carolina, South Carolina, Virginia, Washington, D.C., West Virginia); East South Central (Alabama, Kentucky, Mississippi, Tennessee); West South Central (Arkansas, Louisiana, Oklahoma, Texas); Mountain (Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah, Wyoming); Pacific (Alaska, California, Hawaii, Oregon, Washington).
¥The number and/or proportion of an influenza virus type/subtype may differ between the virus detections reported and the viruses antigenically characterized by CDC because 1) some isolates initially reported as influenza A (unsubtyped) through weekly surveillance may be submitted to CDC for further characterization that will include subtyping of those viruses, and 2) influenza virus type/subtype less frequently seen during a given influenza season may be actively solicited for antigenic characterization. The number and relative proportion of virus type/subtype reported through weekly surveillance should be considered as representative of the currently circulating viruses, whereas antigenic characterization information should be used to compare the relative proportion of a virus strain within a type or subtype.
¶ The expected baseline proportion of P&I deaths reported by the 122 Cities Mortality Reporting System is projected using a robust regression procedure in which a periodic regression model is applied to the observed percentage of deaths from P&I over the previous 5 years. The epidemic threshold is 1.654 standard deviations above the seasonal baseline. 
‡ The Emerging Infections Program (EIP) Influenza Project conducts surveillance in 60 counties associated with 12 metropolitan areas: San Francisco CA, Denver CO, New Haven CT, Atlanta GA, Baltimore MD, Minneapolis/St. Paul MN, Albuquerque NM, Las Cruces, NM, Albany NY, Rochester NY, Portland OR, and Nashville TN.  The New Vaccine Surveillance Network (NVSN) conducts surveillance in Monroe County NY, Hamilton County OH, and Davidson County TN. 
††Active prospective surveillance in the EIP and the NVSN ended as of April 30, 2006 and April 29, 2006, respectively.
§§ The national 2.2% baseline was calculated as the mean percentage of visits for ILI during noninfluenza weeks plus two standard deviations. Because of wide variability in regional level data, calculating region-specific baselines is not possible and to apply the national baseline to regional level data in not appropriate.
¥¥ Data for percentage of patient visits for ILI weighted by state population.

¶¶ Levels of activity are 1) no activity, 2) sporadic—small numbers of laboratory-confirmed influenza cases or a single influenza outbreak reported but no increase in cases of ILI, 3) local—outbreaks of influenza or increases in ILI cases and recent laboratory-confirmed influenza in a single region of a state, 4) regional—outbreaks of influenza or increases in ILI cases and recent laboratory-confirmed influenza in at least two but less than half the regions of a state, and 5) widespread—outbreaks of influenza or increases in ILI cases and recent laboratory-confirmed influenza in at least half the regions of a state.

n the virus detections reported and the viruses antigenically characterized by CDC because 1) some isolates initially reported as influenza A (unsubtyped) through weekly surveillance may be submitted to CDC for further characterization that will include subtyping of those viruses, and 2) influenza virus type/subtype less frequently seen during a given influenza season may be actively solicited for antigenic characterization. The number and relative proportion of virus type/subtype reported through weekly surveillance should be considered as representative of the currently circulating viruses, whereas antigenic characterization information should be used to compare the relative proportion of a virus strain within a type or subtype.
¶ The expected baseline proportion of P&I deaths reported by the 122 Cities Mortality Reporting System is projected using a robust regression procedure in which a periodic regression model is applied to the observed percentage of deaths from P&I over the previous 5 years. The epidemic threshold is 1.654 standard deviations above the seasonal baseline. 
‡ The Emerging Infections Program (EIP) Influenza Project conducts surveillance in 60 counties associated with 12 metropolitan areas: San Francisco CA, Denver CO, New Haven CT, Atlanta GA, Baltimore MD, Minneapolis/St. Paul MN, Albuquerque NM, Las Cruces, NM, Albany NY, Rochester NY, Portland OR, and Nashville TN.  The New Vaccine Surveillance Network (NVSN) conducts surveillance in Monroe County NY, Hamilton County OH, and Davidson County TN. 
††Active prospective surveillance in the EIP and the NVSN ended as of April 30, 2006 and April 29, 2006, respectively.
§§ The national 2.2% baseline was calculated as the mean percentage of visits for ILI during noninfluenza weeks plus two standard deviations. Because of wide variability in regional level data, calculating region-specific baselines is not possible and to apply the national baseline to regional level data in not appropriate.
¥¥ Data for percentage of patient visits for ILI weighted by state population.

¶¶ Levels of activity are 1) no activity, 2) sporadic—small numbers of laboratory-confirmed influenza cases or a single influenza outbreak reported but no increase in cases of ILI, 3) local—outbreaks of influenza or increases in ILI cases and recent laboratory-confirmed influenza in a single region of a state, 4) regional—outbreaks of influenza or increases in ILI cases and recent laboratory-confirmed influenza in at least two but less than half the regions of a state, and 5) widespread—outbreaks of influenza or increases in ILI cases and recent laboratory-confirmed influenza in at least half the regions of a state.