Influenza Trends, September 2009
Influenza viruses in circulation, 2009: Multiple viral subtypes (influenza A subtypes, pandemic H1N1, and influenza B) circulated throughout 2009 in both the Southern and Northern Hemispheres (Figures WO-12 and WO-13).
Southern Hemisphere influenza season: Several countries experienced multiple viral epidemics that included RSV, parainfluenza, and seasonal influenza (both H3N2 and H1N1); in some cases, 2009-H1N1 influenza A overpowered co-infecting viruses to become the predominant respiratory infection. The following figures, depicting annual influenza trends in Chile (Figure WO-14), Australia (Figure WO-15), Hong Kong (Figure WO-16), Cambodia (Figure WO-17), Kenya (Figure WO-18), South Africa (Figure WO-19), and New Zealand (Figure WO-20), illustrate the significance of 2009-H1N1 influenza A in the Southern Hemisphere 2009 influenza season.
As of September 11, 2009, as the Southern Hemisphere influenza season waned, the following trends in ILI were apparent:
SOURCES: Cox (2009); Fukuda (2009); Shortridge (2009).