Table 1
Month of peak influenza activity during 31 influenza seasons - United States, 1976-2006

No. (%) of years with peak influenza activity in a given month

Nov Dec Jan Feb Mar Apr May
1
(3)		 4
(13)		 6
(19)		 14
(45)		 4
(13)		 1
(3)		 1
(3)

The peak week of activity was defined as the week with the greatest percentage of respiratory specimens testing positive for influenza on the basis of a 3 week moving average.  Laboratory data were provided by U.S. World Health Organization Collaborating Centers (CDC, unpublished data, 1976-2006).