Pattern and Process:
Gaining insights from time-space characteristics of disease distribution
Summary
- Disease etiologies: causes and
associations
- meaning of cause: toxins, accidents, microbes, genes, poverty
- time and space considerations:
- time from exposure to outcome
- place of source, exposure, case location
- goals:
- describe (easy)
- evaluate pattern (possibly difficult)
- infer underlying etiological process (very hard!)
- Modes of acquisition
- Exposure to environmental source or event
- "point-source"
- "non-point source"
- Contagion
- direct, human-to-human
- indirect: human-vehicle-human
- direct, animal-to-human
- indirect: animal-vehicle-human
- Questions:
- How do these different modes of acquisition produce similar or
different patterns of disease?
- What different mechanisms can we propose for these
patterns of Disease Spread?
- Here's a spatial
pattern: what would you hypothesize if you could also see its progression over time?
- Try it with another pair:
spatial pattern; progression over time.
- Measurement in time and space - opportunities and problems
- Time measured as
- Exposure event (accident, emission, colonization)
- Symptom onset (problem of incubation period)
- Space can be measured as:
- Location of event (sometimes difficult to define)
- Place of initial exposure (rarely known)
- Residence (often not related to exposure)
- people move (problem with long incubation)
- workplace or school (may not be focal exposure)
- Time-Space interactions may confound
- single observations of little use
- distance from toxin source and intensity
- rate of spread of contagious process and final observation
- 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.]
- Environmental toxins: physical and chemical exposure examples
- Time, space patterns of point source
- Non-point source
- Importance of magnitude of exposure, effect of age, etc.
- Scale is an issue, in both space and time.
- Infectious parasites: contagious or communicable diseases
- Time, space patterns of point source
- Non-point source
- Importance of magnitude of exposure, effect of age, etc.
- Scale is still an issue
- Genetic conditions
- Poverty
Readings
Page by Andy Long.
Comments appreciated.
aelon@sph.umich.edu