DRAFT: This module has unpublished changes.

The Theory of Contagion

DRAFT: This module has unpublished changes.

by Miranda Fadden

DRAFT: This module has unpublished changes.

History of the Theory of Contagion:

The theory of contagion can be credited to Girolamo Fracastoro, an Italian physician, poet, and mathematics scholar [4]. During the 1500s, he first used the word ‘contagion’ while writing about infectious diseases and became famous for his three-fold view of contagion: by indirect contact, contact at a distance, and direct contact [4]. Diseased people were thought to spread disease through indirect contact from their clothes, which contained substances called fomes, classifying the people as contagious [5]. Miasmas, or noxious air, were thought to spread disease to people through contact at a distance, while microorganisms were thought to spread disease through direct contact, as explained by the germ theory of disease [5,7]. John Snow, the father of epidemiology, was skeptic of disease transmission through both indirect contact and miasmas, and sought to disprove both theories [8].  Through the evidence Snow gathered from his work with cholera, he discounted the theory of miasma and came to support the germ theory of disease [8].


Application of Contagion:

In general the word contagion can be defined as a rapidly spreading infection, like the plague or the flu [2]. Although the idea of contagion and contagiousness has been around for thousands of years, it is now more widely used as a metaphor for anything that spreads quickly from person to person [2].  Behavior spreading through a crowd is an example of how contagion can be applied to more than just infectious diseases, as seen through the theory of social contagion.


The Theory of Social Contagion:

The contagion theory of collective behavior (social contagion) has been developed to describe how behaviors can be contagious within a crowd. This theory is based upon the idea that moods and thoughts, both positive and negative, become contagious within certain types of crowds [6]. After having been ‘infected’ with certain thoughts, members of the crowd will start to exhibit behavior that is contradictory to what they would normally do [6]. Figure 1 depicts the social interactions that contribute to the theory of social contagion.

DRAFT: This module has unpublished changes.
User-uploaded Content
DRAFT: This module has unpublished changes.

Figure 1. Adaptation of the Contagion Theory.


Gustave LeBon, a French social psychologist, is most widely known for his work on the social contagion theory (6). LeBon argues that crowds are distinguished by two psychological characteristics that make them more than a simple grouping of individuals (6).  The first characteristic describes the certain suppression of individuality that occurs when crowds start to form (6). Through the suppression of individuality, individuals become increasingly susceptible to others’ thoughts and actions, as reflected in Figure 1. The second characteristic describes the psychological transformation that occurs in an individual’s mind when drawn into a specific crowd (6). LeBon proposed three primary causes of these characteristics: the feeling of invincible power, contagion, and suggestibility (6). The feeling of invincible power comes from the crowd having strength in numbers (6).  Members of the crowd are put under a hypnotic-like trance in which their emotions and actions are more easily spread throughout the crowd, suggesting a sense of contagion (6). Lastly, suggestibility is what drives contagion and is therefore the principle force behind it (6).


Use in Public Health Policies:

For certain behaviors and actions the theory of social contagion should be incorporated into public health policies. An article written for The New York Times asked the question, “are your friends making you fat?” (1). This question makes the reader wonder if the people he/she associates with choose certain behaviors, will they also choose similar behaviors? A study mentioned in the article, found solid evidence suggesting that good behaviors, such as regular exercise or quitting smoking, pass from friend to friend just as a virus might spread from person to person (1).  Public health policies will be successful if they target not only the individuals participating in that particular behavior, but also the people that surround that individual. However, there is one major limitation to that kind of thinking. It suggests that people have very little control over their own actions and simply choose to exhibit behaviors because those around them are exhibiting those behaviors. It is important for public health policies to address both the individual involved in the behavior and give them some responsibility for their actions while at the same time incorporating the people surrounding that individual.


Works Cited:

(1) Thompson C. Are your friends making you fat?'. The New York Times. 10 September 2009: MM28.
(2) Collective behavior: contagion theory research [Internet]. 2015 [cited 2015 March 17]. Avialable from: http://www.enotes.com/research-starters/collective-behavior-contagion-theory.
3. Concepts of contagion and epidemics [Internet] 2014 [cited 2015 March 17]. Available from: http://ocp.hul.harvard.edu/contagion/concepts.html.
4. Boran E. Theories of contagion [Internet]. 2015 [cited 2015 March 17] . Available from: http://infectiousdiseases.edwardworthlibrary.ie/theory-of-contagion (accessed 17 March 2015).
5. Nutton V. The reception of Fracastoro's theory of contagion: the seed that fell among thorns?. History of Science Society 1990; 6(1): 196-234.

6. Locher D. Collective behavior [Internet]. Upper Saddle River, New Jersey: Prentice Hall; 2001. [cited 2015 March 17]. Available from: http://sociology.morrisville.edu/readings/SOCI360/Locher%20-%20Chp%202%20-%20Social%20Contagion.pdf


Additional Sources:

Collective Behavior by David Locher.


The Crowd: A Study of the Popular Mind by Gustave LeBon. Found at: http://www.gutenberg.org/cache/epub/445/pg445.html


Memetics and Social Contagion: Two Sides of the Same Coin? Article by Paula Marsden. Found at: http://web.stanford.edu/~kcarmel/CC_BehavChange_Course...


The Spread of Obesity in a Large Social Network Over 32 Years. Article by Nicholas Christakis and James Fowler. Found at: http://www.nejm.org/doi/pdf/10.1056/NEJMsa066082


Are Health (and Unhealthy) Habits Contagious? Article by David Hamilton. Found at: http://www.huffingtonpost.com/david-r-hamilton-phd/health-social-networks_b_867433.html

DRAFT: This module has unpublished changes.