Influenza pandemics provide good case-study material for looking at the spread of infections.
Detailed records were kept of the spread of the 1957 influenza epidemic in northern England. This began in the urban centres. They formed the foci, since their high population densities made transmission more effective. By September the surrounding areas were also affected, but it was not until October that the truly rural areas had cases at an epidemic level.
The 1918 influenza pandemic across the United States originated on the East Coast. As before, the disease next affected larger centres and finally the rural hinterlands.
It is interesting to apply the diffusion model to the 1957 epidemic. This is visualised in the animation below.
Examining the 1957 pandemic
Answer the following questions with a, b or c. Answeres are at the end. 1) The 1957 influenza pandemic affected Northern England by starting in a) small towns, b) rural areas, or c) cities. 2) This was because people in those areas a) were less robust, b) were mixing with large numbers of other people, or c) were travelling widely. 3) The way in which the disease spread was by a) people moving to towns, b) people in confined conditions, or c) town dwellers travelling into smaller rural settlements. 4) The diffusion model which best fits this pattern is a) expansion diffusion, b) expansion and relocation diffusion combined, or c) relocation diffusion.
Answers: 1a) Not quite - fewer people in this area meant less mixing and a slower infection rate. 1b) Not quite - very low population densities meant that the population was isolated from sources of infection for a long time. 1c) Correct - high population densities made diseases transmission more effective. 2a) Not quite - everyone is at risk (susceptible) with a new influenza strain but with less contact with others the risk is lessened. 2b) Correct - since influenza is transmitted mainly as a droplet infection, mixing with many other people makes a person likely to become infected. 2c) Not quite - with high population densities there is no need to travel to come into contact with a large number of infecteds. 3a) Not quite - the process can be two-way; the movement does not have to be permanent. 3b) Not quite - a single sneeze can carry droplet infections over a wide area; infecteds can affect many susceptibles without being confined. 3c) Correct - there is always movement to and from country to town; it was inevitable that the virus should spread in this way eventually. 4a) Not quite - the area of infecteds spreads out but also has several focal points. 4b) Correct - this gives a more realistic picture of a growing number of focal points for infection. 4c) Not quite - original focal points continue to be important even though there are new ones too.
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Geography of health
The diffusion model and influenza pandemics
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