Each week CDC analyzes information about influenza disease activity in the United States and publishes findings of key flu indicators in a report called FluView. During the week of November 29-December 5, 2009, influenza activity decreased over the previous week across all key indicators except for deaths, but most indicators remain higher than normal for this time of year. Below is a summary of the most recent key indicators:
- Visits to doctors for influenza-like illness (ILI) nationally decreased again this week over last week. This is the sixth consecutive week of national decreases in ILI after four consecutive weeks of sharp increases. While ILI has declined, visits to doctors for influenza-like illness remain elevated nationally.
- Influenza hospitalization rates have decreased across all age groups but remain higher than expected for this time of year. Though declining, hospitalization rates continue to be highest in children 0-4 years old.
- The proportion of deaths attributed to pneumonia and influenza (P&I) based on the 122 Cities Report increased over the previous week and has been higher than expected for ten consecutive weeks. In addition, 16 flu-related pediatric deaths were reported this week: 13 of these deaths were associated with laboratory confirmed 2009 H1N1, 2 were associated with influenza A viruses that were not subtyped and one was associated with a seasonal influenza B virus. Since April 2009, CDC has received reports of 267 laboratory-confirmed pediatric deaths: 224 due to 2009 H1N1, 41 pediatric deaths that were laboratory confirmed as influenza, but the flu virus subtype was not determined, and two pediatric deaths were associated with seasonal influenza viruses. (Laboratory-confirmed deaths are thought to represent an undercount of the actual number. CDC has provided estimates about the number of 2009 H1N1 cases and related hospitalizations and deaths. The increase in the proportion of deaths as other indicators are going down is not surprising as the occurrence and reporting of deaths usually lags behind that of other indicators.
- Fourteen states are reporting widespread influenza activity; a decline of 11 states from last week. They are: Alabama, Alaska, Arizona, California, Connecticut, Delaware, Kentucky, Maine, New Hampshire, New Jersey, New York, Rhode Island, Vermont, and Virginia
- Almost all of the influenza viruses identified so far continue to be 2009 H1N1 influenza A viruses. These viruses remain similar to the virus chosen for the 2009 H1N1 vaccine, and remain susceptible to the antiviral drugs oseltamivir and zanamivir with rare exception.