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H1N1 Drove Late Surge in 2008-2009 Flu Season
Novel Influenza A:H1N1 accounted for the majority of confirmed late-season flu cases across the nation. Although overall flu-related deaths held steady, there was a late spike in pediatric deaths.
A Unique Flu Season
CDC data for 2008-2009 show a late-season H1N1 surge in each of ten US Regions. The accompanying graph shows a pattern similar to the US in Region V, which includes Indiana, Illinois, Michigan, Minnesota, Ohio and Wisconsin. The late peak stands out compared to the "monophasic" recent previous flu seasons (graph).
Overall Flu-Related Deaths Stable
Despite the late-season surge in cases, overall deaths did not reach epidemic numbers in the 122 Cities Mortality Reporting System for pneumonia and influenza (known as P&I deaths, pneumonia being the most common fatal complication of influenza).
The following graphs, which were published over time by the CDC, put 2008-2009 in perspective with the previous 10 seasons. The lower smooth line represents the expected rate of pneumonia and influenza deaths (percent of total deaths), which goes up and down predictably with each season. Above it is the rate of deaths that would represent a significant increase, or the so-called 'epidemic threshold.' Reported deaths make the jagged line that crosses the epidemic threshold for several weeks about every 2-3 years. Despite its late peak of cases, 2008-2009 was not one of the epidemic seasons. It appears as the most recent (furthest right) inflection on the furthest right graph.
Of course the question on everyone's mind, is what the next season will hold.
Pediatric Deaths Not as Reassuring
Child pneumonia and influenza mortality showed a late surge in the 2008-2009 season, which in turn appeared to drive a record number of deaths, at least since the current child P&I reporting program was begun in 2004.
For details and latest updates, visit the CDC flu page:
