Matthew Smallman-Raynor & Andrew D. Cliff
This article examines the geographical transmission of an epidemic disease in the makeshift encampments of a mobilized army. The choice of location (the southern and eastern United States), the time (an eight-month period of mobilization in the U.S. war with Spain, May to December 1898) and the epidemic disease (typhoid fever) are conditioned by the reports collated by three eminent figures in the history of medicine–Major Walter Reed, Major Victor C. Vaughan, and Major Edward O. Shakespeare–and published in the historic 1904 Report on the Origin and Spread of Typhoid Fever in U.S. Military Camps During the Spanish War of 1898. The Report includes information on the daily occurrence of some 19,000 cases of typhoid fever in 89 volunteer regiments of the U.S. Army. When geo-coded to the locations of army camps, this information is used (i) to reconstruct the spread of typhoid fever with the campwise movements of infected regiments and (ii) to model the diffusion process that drove the spread of the disease. To handle the high degree of regimental mobility in the camp system, a novel process referred to as transfer diffusion is introduced. It is shown that, for the entire system of camps, the spread of typhoid was underpinned by a temporally ordered sequence of diffusion processes in which each process was associated with a discrete stage of the epidemic cycle. The processes reflected the spatial transfer of regiments (epidemic buildup), the geographical proximity of camps (epidemic peak), and the position of camps in the transient population size hierarchy (epidemic fadeout). Importantly, however, the strength and timing of the processes varied by corps. While the findings underscore the singular impact of military mobilization on the spatial dynamics of epidemic diseases, it is suggested that the particular approach adopted in this article may be extended to the study of epidemic transmission in analogous camp settings.
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