Disease diffusion mapping

Disease diffusion occurs when a disease is transmitted to a new location.[1] It implies that a disease spreads, or pours out, from a central source.[2] The idea of showing the spread of disease using a diffusion pattern is relatively modern, compared to earlier methods of mapping disease, which are still used today.[3] According to Rytokonen, the goals of disease mapping are: 1) to describe the spatial variation in disease incidence to formulate an etiological hypothesis; 2) to identify areas of high risk in order to increase prevention; and 3) to provide a map of disease risk for a region for better risk preparedness.[4]

Torsten Hägerstrand’s early work on “waves of innovation” is the basis that many medical cartographers and geographers use for mapping spatial diffusion (1968).[5] The diffusion of disease can be described in four patterns: expansion diffusion, contagious diffusion, hierarchal diffusion and relocation diffusion.[6] Cromley and McLafferty also mention network diffusion and mixed diffusion.[1]

The diffusion of infectious disease tends to occur in a ‘wave’ fashion, spreading from a central source. Pyle mentions barriers that pose a resistance towards a wave of diffusion, which include but are not limited to: physiographic features (i.e. mountains, water bodies), political boundaries, linguistic barriers, and with diseases, a barrier could be differing control programs.[7] The diffusion of disease can be identified as a normal distribution over time and translated into an S-shaped curve to show the phases of disease diffusion. The phases are: Infusion (25th percentile), Inflection (50th percentile), Saturation (75th percentile), and Waning to the upper limits.[8]

Disease diffusion types

Spreading wildfire showing expansion diffusion

The value of mapping and Geographic Information Systems (GIS) is becoming better known to public health professionals to help link disease control to prevention efforts, which can aid in developing better immunization programs.[11] GIS is an excellent tool used to identify spatial patterns and core areas of disease transmission. Disease maps can distinguish the low and high risk areas, as well as highlight “physical and/or socio-cultural” factors that contribute to the causation of disease.[12] Understanding how a disease spreads gives health officials a better understanding of how to better serve the public.

References

  1. 1 2 Cromley, Ellen K. and Sarah L. McLafferty. GIS and Public Health. The Guilford Press, New York, 2002. pp. 189-209
  2. Pyle, Gerald F. “Studies of Disease Diffusion.” Applied Medical Geography. V.H. Winston & Sons, Washington, D.C., 1979: pp. 123
  3. Walter, S.D. “Disease Mapping: a historical perspective.” Spatial Epidemiology: Methods and Applications. Eds. P. Elliot, J.C. Wakfield, N.G. Best, and D.J. Briggs. Oxford University Press, 2000. pp. 225
  4. Rytokonen, Mike, JP. “Not All Maps are Equal: GIS and Spatial Analysis in Epidemiology.” International Journal of Circumpolar Health 63:1, 2004: pp. 11
  5. Koch, Tom. Geographies of Disease: Maps, Mapping, and Medicine. ESRI Press. Redlands, California, 2005. Ch. 10, pp. 249-281
  6. Hornsby, 2000 from Cliff et al. 1981: Pyle, 1979, 137 from Gould, 1969
  7. Pyle, Gerald F. “Studies of Disease Diffusion.” Applied Medical Geography. V.H. Winston & Sons, Washington, D.C., 1979: pp. 138
  8. Pyle, Gerald F. “Studies of Disease Diffusion.” Applied Medical Geography. V.H. Winston & Sons, Washington, D.C., 1979: pp. 139
  9. 1 2 Cromley, Ellen K. and Sarah L. McLafferty. GIS and Public Health. The Guilford Press, New York, 2002. pp. 192
  10. Hornsby, Kathleen. “Spatial Diffusion: Conceptualizations and Formalizations.” National Center for Geographic Information and Analysis and Department of Spatial Information Science and Engineering, University of Maine, 2000: Pyle, Gerald F. “Studies of Disease Diffusion.” Applied Medical Geography. V.H. Winston & Sons, Washington, D.C., 1979: pp. 123-163
  11. Cromley, Ellen K. and Sarah L. McLafferty. GIS and Public Health. The Guilford Press, New York, 2002. pp. 194
  12. Rytkonen, Mika, JP. “Not All Maps are Equal: GIS and Spatial Analysis in Epidemiology.” International Journal of Circumpolar Health 63:1, 2004: pp. 18

4. Rytkönen, Mika JP. “Not All Maps are Equal: GIS and Spatial Analysis in Epidemiology.” International Journal of Circumpolar Health 63:1, 2004: pp. 11 Available: http://www.circumpolarhealthjournal.net/index.php/ijch/article/viewFile/17642/20108

Further reading

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