Mean estimates of the reproduction number and corresponding 95% CIs for the spring, summer, and fall waves of the 2009 A/H1N1 influenza pandemic by geographic region.

The latent and infectious periods are assumed to be exponentially distributed with a serial interval of 3 and 4 d. The epidemic growth phase used to estimate the R consisted of 14 d for the spring wave (April 12–April 25) and summer wave (May 21–June 3) and 28 d for the fall wave in central states (August 5–September 1) and northern states (August 8–September 4).See Text S1, figure K, for exact time periods considered as part of the epidemic growth phase.