Pattern and Process: Gaining insights from time-space characteristics of disease distribution

1. Disease etiologies: causes and associations
   1. meaning of cause: toxins, accidents, microbes, genes, poverty
   2. time and space considerations:
      1. time from exposure to outcome
      2. place of source, exposure, case location
   3. goals:
      1. describe (easy)
      2. evaluate pattern (possibly difficult)
      3. infer underlying etiological process (very hard!)

2. Modes of acquisition
   1. Exposure to environmental source or event
      1. "point-source"
      2. "non-point source"
   2. Contagion
      1. direct, human-to-human
      2. indirect: human-vehicle-human
      3. direct, animal-to-human
      4. indirect: animal-vehicle-human
   3. Questions:
      1. How do these different modes of acquisition produce similar or different patterns of disease?
      2. What different mechanisms can we propose for these patterns of Disease Spread?
      3. Here's a spatial pattern: what would you hypothesize if you could also see its progression over time?
      4. Try it with another pair: spatial pattern; progression over time.

3. Measurement in time and space - opportunities and problems
   1. Time measured as
      1. Exposure event (accident, emission, colonization)
      2. Symptom onset (problem of incubation period)
   2. Space can be measured as:
      1. Location of event (sometimes difficult to define)
      2. Place of initial exposure (rarely known)
      3. Residence (often not related to exposure)
         1. people move (problem with long incubation)
         2. workplace or school (may not be focal exposure)
   3. Time-Space interactions may confound
      1. single observations of little use
      2. distance from toxin source and intensity
      3. rate of spread of contagious process and final observation
      4. need for "epidemic" curve
   What patterns should be expected for the following?

   [In class we work together on this table in an attempt to derive an idea of the relationship we'd expect between pattern and processes.]

4. Environmental toxins: physical and chemical exposure examples
   1. Time, space patterns of point source
   2. Non-point source
   3. Importance of magnitude of exposure, effect of age, etc.
   4. Scale is an issue, in both space and time.

5. Infectious parasites: contagious or communicable diseases
   1. Time, space patterns of point source
   2. Non-point source
   3. Importance of magnitude of exposure, effect of age, etc.
   4. Scale is still an issue

6. Genetic conditions

7. Poverty

Page by Andy Long. Comments appreciated.