For week 48 in the United States (25 November – 1 December), influenza activity increased.
Of 5,511 specimens submitted, 1,139 (20.7%) were positive for influenza. Of these, 854 (75%) were influenza A and 285 (25%) were influenza B. Of the influenza A virus positive specimens, 4 were H1N1 (2009) and 406 contained the H3 HA. The remainder (444) were not subtyped. It is curious that the H3N2 virus, which emerged in 1968, has largely displaced the 2009 H1N1 virus.
