This map posted by the CDC on May 28 shows activity of 2009 H1N1 ”Swine Flu” nationwide during the week ending May 22, 2010.  This is the final CDC update map for the 2009-2010 season. The map is updated weekly, but there is a one week lag between data collection and data availability. The current map shows that virtually the entire country is reporting either sporadic activity (light brown) or no activity at all. Only Hawaii is reporting “local” activity, the next level up from sporadic. The second wave of Swine flu reached its greatest extent during the week of Oct 23 2009, when all but one state in the continental US was reporting widespread activity. As recently as Nov 21,  widespread activity was still reported in the majority of the states in the US. During Christmas week there were 7 states reporting widespread flu activity and 18 reporting regional activity. 

No state has reported widespread activity since the second week of January 2010.  There was a persistence of regional activity in the Southeast US that lasted from mid-January to mid-April, but that has abated.  This is the same region where the second wave of Swine Flu began in August 2009.

These data indicate that the second wave of the H1N1 outbreak that began in late August 2009 is over. The first wave appeared from April to August of 2009. There was some speculation that the persistence of regional activity in the US Southeast into April of 2010 could signal a “third wave”,  but given the diminution in flu activity even in this region over the past 4-6 weeks, a third wave does not appear to be imminent. Both the CDC and WHO have predicted that 2009 H1N1 will be the predominant strain of flu in circulation in the coming 2010-2011 influenza season, and for that reason the routine influenza vaccine for next season will include protection against 2009 H1N1.

This is the last CDC update on the 2009-2010 flu season. Data are colleced on flu activity through the summer months, but the weekly updates will not start again until the official beginning of the 2010-2011 flu season in October 2010 .

Click here to find the Flu View weekly update maps from CDC. Scroll to the bottom of that web page, then click on the tab for “previous week” to see the weekly maps in reverse consecutive order as far back as October 2008. This encompasses both the seasonal flu during the 2008-2009 flu season as well as waves one and two of the Swine Flu pandemic from April 2009 to April 2010.

An explanation from CDC for each category follows:

Summary of the Geographic Spread of Influenza — State health departments report the estimated level of influenza activity in their state each week through the State and Territorial Epidemiologists Reports. States report influenza activity as no activity, sporadic, local, regional, or widespread. These levels are defined as follows:

• No Activity: No laboratory-confirmed cases of influenza and no reported increase in the number of cases of ILI.
• Sporadic: Small numbers of laboratory-confirmed influenza cases or a single laboratory-confirmed influenza outbreak has been reported, but there is no increase in cases of ILI.
• Local: Outbreaks of influenza or increases in ILI cases and recent laboratory-confirmed influenza in a single region of the state.
• Regional:Outbreaks of influenza or increases in ILI and recent laboratory confirmed influenza in at least two but less than half the regions of the state with recent laboratory evidence of influenza in those regions.
• Widespread:Outbreaks of influenza or increases in ILI cases and recent laboratory-confirmed influenza in at least half the regions of the state with recent laboratory evidence of influenza in the state.

Click here for the actual CDC site with further information.