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Centers for Disease Control and Prevention

Influenza Summary Update
(Week ending October 14, 2000-Week 41)

The following information may be quoted:

Synopsis: During week 41 (October 8-14, 2000), two of the specimens tested by WHO and NREVSS laboratories were positive for influenza A(H1N1) 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 8 of 9 surveillance regions. The proportion of deaths attributed to pneumonia and influenza was 6.7%. This percentage is below the epidemic threshold for this time of year. One state and territorial health department reported regional influenza activity, 9 reported sporadic activity, and 38 reported no influenza activity.

U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) Collaborating Laboratory Reports* : During week 41, WHO and NREVSS laboratories reported 421 specimens tested for influenza viruses. Two influenza A (H1N1) isolates were identified.

Pneumonia and Influenza (P&I) Mortality: During week 41, the percentage of all deaths due to P&I as reported by the vital statistics offices of 122 U.S. cities was 6.7%.  This percentage is below the epidemic threshold of 7.3% for week 41.

Prior to the 1999-2000 season, a new case definition for a P&I 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 did 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 41, 1% 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 8 of 9 surveillance regions. In the Pacific region, 4% of patient visits were due to ILI. This number should be interpreted with caution because only 8 physicians in this region had reported by the time this report was prepared.

Influenza Activity as Assessed by State and Territorial Epidemiologists**: Influenza activity was reported as regional in 1 state (Maryland) and sporadic in 9 states (Alaska, California, Indiana, Kansas, Kentucky, Nevada, New Hampshire, New Mexico, and West Virginia). Thirty-eight states reported no influenza activity, and 2 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 19, 2000

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

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