Empirical Evidence for the Effect of Airline Travel on Inter-Regional Influenza Spread in the United States
Figure 2
Major Geographic Regions of the United States
The sentinel cities that report mortality due to P&I used in the Centers for Disease Control and Prevention 122 Cities Mortality Reporting System are displayed (black dots). Because the strength of the seasonal influenza cycle is weak for cities with small case counts and because some city data contain missing data points, we aggregated the raw city-level data to obtain composite waveforms by major geographic region, the aerial unit of analysis for this study.