Epidemiology and Infection

Original Papers

The impact of a physical geographic barrier on the dynamics of measles

A. VORAa1, D. S. BURKEa2a3 and D. A. T. CUMMINGSa2a3 c1

a1 School of Medicine, Johns Hopkins University, Baltimore, MD, USA

a2 Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD, USA

a3 Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA, USA

Abstract

Spatial–temporal patterns of measles incidence reflect the spatial distribution of human hosts. The heterogeneous spatial distribution of communities has been shown to introduce spatially dependent temporal lags in the timing of measles incidence. Incidence patterns reflect internal dynamics within a community and coupling of communities through the movement of infectious individuals. The central role of human movement in coupling dynamics in separate communities suggests that physical geographic barriers to movement should reduce spatial–temporal correlation. We examine measles dynamics in Maryland and Pennsylvania during the period of 1917–1938. The central feature of interest is the Chesapeake Bay, which separates Maryland into two distinct regions. We find that correlation of measles incidences in communities separated by the bay is reduced compared to communities not separated by the bay, suggesting the bay acted as a barrier to human movement during this time sufficient to decouple measles dynamics in Maryland counties.

(Accepted June 06 2007)

(Online publication July 30 2007)

Correspondence:

c1 Author for correspondence: Dr D. A. T. Cummings, Department of Epidemiology, Bloomberg School of Public Health, 615 N. Wolfe Street, Rm. E6138, Baltimore, MD 21205, USA. (Email: derek.cummings@jhu.edu)

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