Local variations in spatial synchrony of influenza epidemics.
BACKGROUND
Understanding the mechanism of influenza spread across multiple geographic scales is not complete. While the mechanism of dissemination across regions and states of the United States has been described, understanding the determinants of dissemination between counties has not been elucidated. The paucity of high resolution spatial-temporal influenza incidence data to evaluate disease structure is often not available.


RESULTS
We report on the underlying relationship between the spread of influenza and human movement between counties of one state. Significant synchrony in the timing of epidemics exists across the entire state and decay with distance (regional correlation=62%). Synchrony as a function of population size display evidence of hierarchical spread with more synchronized epidemics occurring among the most populated counties. A gravity model describing movement between two populations is a stronger predictor of influenza spread than adult movement to and from workplaces suggesting that non-routine and leisure travel drive local epidemics.


CONCLUSIONS
These findings highlight the complex nature of influenza spread across multiple geographic scales.
Division of Epidemiology, New York City Department of Health and Mental Hygiene, New York, New York, USA. jstark@health.nyc.gov
James H
JH
Stark
Derek A T
DA
Cummings
Bard
B
Ermentrout
Stephen
S
Ostroff
Ravi
R
Sharma
Samuel
S
Stebbins
Donald S
DS
Burke
Stephen R
SR
Wisniewski
D004196:Disease Outbreaks; D006801:Humans; D007251:Influenza, Human / Q000453:epidemiology*; D011156:Population Density