Spatial and temporal structure of typhoid outbreaks in Washington, D.C., 1906-1909: evaluating local clustering with the Gi* statistic.
BACKGROUND
To better understand the distribution of typhoid outbreaks in Washington, D.C., the U.S. Public Health Service (PHS) conducted four investigations of typhoid fever. These studies included maps of cases reported between 1 May - 31 October 1906 - 1909. These data were entered into a GIS database and analyzed using Ripley's K-function followed by the Gi* statistic in yearly intervals to evaluate spatial clustering, the scale of clustering, and the temporal stability of these clusters.


RESULTS
The Ripley's K-function indicated no global spatial autocorrelation. The Gi* statistic indicated clustering of typhoid at multiple scales across the four year time period, refuting the conclusions drawn in all four PHS reports concerning the distribution of cases. While the PHS reports suggested an even distribution of the disease, this study quantified both areas of localized disease clustering, as well as mobile larger regions of clustering. Thus, indicating both highly localized and periodic generalized sources of infection within the city.


CONCLUSIONS
The methodology applied in this study was useful for evaluating the spatial distribution and annual-level temporal patterns of typhoid outbreaks in Washington, D.C. from 1906 to 1909. While advanced spatial analyses of historical data sets must be interpreted with caution, this study does suggest that there is utility in these types of analyses and that they provide new insights into the urban patterns of typhoid outbreaks during the early part of the twentieth century.
World Health Organization Collaborating Center for Remote Sensing and GIS for Public Health, Department of Geography and Anthropology, Louisiana State University, Howe-Russell Geoscience Complex, Baton Rouge, Louisiana, USA. shinma1@lsu.edu
Sarah E
SE
Hinman
Jason K
JK
Blackburn
Andrew
A
Curtis
D004196:Disease Outbreaks / Q000266:history* / Q000706:statistics & numerical data; D004219:District of Columbia / Q000453:epidemiology; D040362:Geographic Information Systems; D049673:History, 20th Century; D006801:Humans; D015233:Models, Statistical; D014435:Typhoid Fever / Q000453:epidemiology / Q000266:history*