Synopsis: During week 40 (October 1-7, 2000), none of the specimens tested by WHO and NREVSS laboratories were positive for influenza virus.  The proportion of patient visits to sentinel physicians for influenza-like illness was within baseline levels of 0% to 3% in the United States overall and in all 9 surveillance regions. The proportion of deaths attributed to pneumonia and influenza was 6.4%. This percentage is below expected levels for this time of year. Eight state and territorial health departments reported sporadic influenza activity and 35 reported no influenza activity.

U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) Collaborating Laboratory Reports*: During week 40, WHO and NREVSS laboratories reported 426 specimens tested for influenza viruses. No influenza isolates were identified.

Summer isolates from other sources: During June and July, laboratory-confirmed influenza A (H1N1) infections were reported in Texas.   Some of these infections were associated with an outbreak at a children’s summer camp.  In September, CDC received an influenza B isolate from Alaska for antigenic characterization.  Additional reports of laboratory-confirmed influenza B infections have been reported from Washington, Nevada, and California during August and September. California also reported laboratory-confirmed influenza A infections during September.

Pneumonia and Influenza (P&I) Mortality: During week 40, the percentage of all deaths due to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 6.4%. This percentage is below the epidemic threshold of 7.2% for week 40. Prior to the 1999-2000 season, a new case definition for a pneumonia and influenza death was introduced in the 122 Cities Mortality Reporting System.  It was recognized that one potential effect of using this case definition was to increase P&I mortality measurement levels in comparison to previous seasons.  During the summer of 2000, the P&I mortality data were analyzed to determine if the modified case definition had affected mortality estimates.  On the basis of this analysis, we estimate that there was an approximately 0.8% upward shift in 1999-2000 mortality estimates. The 0.8% shift does not represent a true increase in mortality.  To adjust for this upward shift in mortality estimates, the 122 cities P&I mortality baseline and epidemic threshold for the 2000-01 season have been adjusted upward as well. 

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Influenza Morbidity Reports from U.S. Sentinel Physicians*: During week 40, 2% of patient visits to U.S. sentinel physicians were due to influenza-like illness (ILI). The percentage of ILI was within baseline levels of 0% to 3% in all 9 surveillance regions.

Influenza Activity as Assessed by State and Territorial Epidemiologists**: Influenza activity was reported as sporadic in 8 states (Alaska, California, Colorado, Florida, Indiana, Kentucky, Ohio, and West Virginia). Thirty-five states reported no influenza activity, and 7 did not report

* Reporting is incomplete for this week. Numbers may change as more reports are received.

** Influenza activity is defined as influenza-like illness and/or culture-confirmed influenza.

     Report prepared: October 12, 2000

Appendix I: 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

National Center for Infectious Diseases
Centers for Disease Control and Prevention
Atlanta, GA

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