Brian Altonen, MPH, MS

The Diffusion of diseases in this country follow several spatial patterns and abide by specific temporal patterns.  

   The simplest spatial model for diffusion is the radial or linear process with follows either just the air and is impacted by wind flow patterns (radial), or travels a natural route of least resistance such as through a gully, along a woodlands edge, parallel to roadways and animal migration routes (linear).

   A more complex spatial model follows human migration and travel patterns and certain commercial or economic paths.  The most human dependent ironically abide by many of the same patterns that inventions and discoveries tend to follow.  They hierarchically diffuse from one area to the next, going from large population area to large population area and then back-tracking to smaller areas between these major landing or outbreak areas.

   In some cases, especially when poverty becomes a major issue in how a disease develops, a reversed hierarchical pattern develops.  That is to say they at first behave hierarchically, moving from one large area to the next, but each time they reach a new population center, they infect the most susceptible populations.  In most urban settings, for numerous regions low income, low socioeconomic status neighborhoods become the places where many of these disease develop, or adapt to human population features and human behaviors to help find the next susceptible victims.  Cholera is an example that migrates internationally in this fashion.  The most susceptible areas and people are typically low income groups residing in low property value settings (poor managed, filthy, least desirable living places.)

   The temporal pattern of disease flow is related to how it travels and at what rate across the earth’s surface.  As recent diseases making their way to the United States from other countries demonstrate, distance is no longer a deterrent to international disease spread.  Even Australia, more than 10,000 miles away from the center of the U.S., is capable of sending its next disease or vector to the U.S.

   This review of how diseases that make their way to Chicago fits the current dilemma we are in with international disease migration patterns and concerns.  The spread of MERS into the more southern midwestern regions of the U.S., demonstrates a possible mixed diffusion pattern.  The early stages appear to be linear or radial in nature based on transportation routes, but should this disease take off and produce an outbreak, hierarchical diffusion patterns are expected as well.