Univariate regression of timing of RSV activity in 50 US states and District of Columbia, 1989–2010, against monthly climatic, population and geographic indicators.

Separate models are built for phase timing (average weekly phase difference with Florida, the earliest RSV state) and center of gravity (weighted average of RSV epidemic week, where each week is weighted by the number of RSV cases). All epidemic measures are based on weekly laboratory-reported RSV time series. Boldface indicates significance (p<0.05) in the exploratory analysis.
* p<0.05; ** p<0.01; *** p<0.0001
aAverage value for September, October, and November.
bMinimum, maximum and average monthly temperatures were considered. R2 represents the range for the 3 variables. In all models, minimum temperature was the most strongly associated with RSV timing; hence parameter estimates listed in this table are for minimum temperature.
Univariate regression of timing of RSV activity in 50 US states and District of Columbia, 1989–2010, against monthly climatic, population and geographic indicators.