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 December 20-26, 2009, certain key indicators decreased, others increased, and still others remained the same compared to the previous week. Below is a summary of the most recent key indicators:
Visits to doctors for influenza-like illness (ILI) nationally increased slightly this week over last week. This is the first increase in this indicator after eight consecutive weeks of national decreases. The increase in the percentage of visits to doctors for ILI during this is likely influenced by fewer people going to the doctor for routine health care visits during the holiday season, as has occurred during previous seasons.
Overall hospitalization rates for this season were unchanged from the previous week in all age groups.
The proportion of deaths attributed to pneumonia and influenza (P&I) based on the 122 Cities Report increased over the previous week and is now back above the epidemic threshold after dipping below it last week for the first time in 11 weeks. (The epidemic threshold is the point at which the observed proportion of deaths attributed to pneumonia or influenza is significantly higher than would be expected at that time of the year in the absence of substantial influenza-related mortality.)
In addition, four flu-related pediatric deaths were reported this week compared to 9 reported last week: two of these deaths reported this week were associated with laboratory confirmed 2009 H1N1, and two were associated with influenza A viruses that were not subtyped. Since April 2009, CDC has received reports of 289 laboratory-confirmed pediatric deaths: 243 due to 2009 H1N1, 44 pediatric deaths that were laboratory confirmed as influenza, but the flu virus subtype was not determined, and two pediatric deaths that 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.
Four states are reporting widespread influenza activity; a decline of three states from last week. They are: Delaware, Maine, New Jersey 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.
*All data are preliminary and may change as more reports are received.