Disease diffusion occurs when a

disease A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...

is transmitted to a new location.Cromley, Ellen K. and Sarah L. McLafferty. GIS and Public Health. The Guilford Press, New York, 2002. pp. 189-209 It implies that a disease spreads, or pours out, from a central source. The idea of showing the spread of disease using a

diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemica ...

pattern is relatively modern, compared to earlier methods of mapping disease, which are still used today. According to Rytokonen, the goals of disease mapping are: 1) to describe the spatial variation in disease incidence to formulate an

etiological Etiology (pronounced ; alternatively: aetiology or ætiology) is the study of causation or origination. The word is derived from the Greek (''aitiología'') "giving a reason for" (, ''aitía'', "cause"); and ('' -logía''). More completely, e ...

hypothesis; 2) to identify areas of high risk in order to increase prevention; and 3) to provide a

map A map is a symbolic depiction emphasizing relationships between elements of some space, such as objects, regions, or themes. Many maps are static, fixed to paper or some other durable medium, while others are dynamic or interactive. Although ...

of disease risk for a region for better risk preparedness.

Torsten Hägerstrand Torsten Hägerstrand (October 11, 1916, in Moheda – May 3, 2004, in Lund) was a Swedish geographer. He is known for his work on migration, cultural diffusion and time geography. A native and resident of Sweden, Hägerstrand was a professor (l ...

’s early work on “waves of

innovation Innovation is the practical implementation of ideas that result in the introduction of new goods or services or improvement in offering goods or services. ISO TC 279 in the standard ISO 56000:2020 defines innovation as "a new or changed entit ...

” is the basis that many medical

cartographers Cartography (; from grc, χάρτης , "papyrus, sheet of paper, map"; and , "write") is the study and practice of making and using maps. Combining science, aesthetics and technique, cartography builds on the premise that reality (or an i ...

and

geographer A geographer is a physical scientist, social scientist or humanist whose area of study is geography, the study of Earth's natural environment and human society, including how society and nature interacts. The Greek prefix "geo" means "earth" a ...

s use for mapping spatial diffusion (1968). The diffusion of disease can be described in four patterns: expansion diffusion, contagious diffusion, hierarchal diffusion and relocation diffusion. Cromley and McLafferty also mention network diffusion and mixed diffusion. The diffusion of

infectious disease An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable di ...

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. The diffusion of disease can be identified as a

normal distribution In statistics, a normal distribution or Gaussian distribution is a type of continuous probability distribution for a real-valued random variable. The general form of its probability density function is : f(x) = \frac e^ The parameter \mu ...

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.

Disease diffusion types

*''Expansion diffusion'' occurs when the spreading phenomenon has a source and diffuses outwards into new areas, an example being a spreading

wildfire A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identi ...

. *''Relocation diffusion'' occurs when the spreading

phenomenon A phenomenon ( : phenomena) is an observable event. The term came into its modern philosophical usage through Immanuel Kant, who contrasted it with the noumenon, which ''cannot'' be directly observed. Kant was heavily influenced by Gottfried ...

migrates into new areas, leaving behind its origin or source of the disease. *''Contagious diffusion'' is the spread of an infectious disease through the direct contact of individuals with those infected. *''Hierarchal diffusion'' occurs when a phenomenon spreads through an ordered sequence of classes or places. *''Network diffusion'' occurs when a disease spreads via transportation and social networks, "reflecting the geographical and social structuring of human interactions".Cromley, Ellen K. and Sarah L. McLafferty. GIS and Public Health. The Guilford Press, New York, 2002. pp. 192 *''Mixed diffusion'' is a combination of contagious diffusion and hierarchal diffusion. AIDS is a prominent example in modern-day society of a mixed diffusion disease, often spreading along the hierarchal, network, and contagious diffusion patterns. 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. 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.Rytkonen, Mika, JP. "Not All Maps are Equal: GIS and Spatial Analysis in Epidemiology." ''International Journal of Circumpolar Health'' 63:1, 2004: pp. 18 Understanding how a disease spreads gives health officials a better understanding of how to better serve the public.

References

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

Disease diffusion types

References

Further reading