title: Suicide contagion: a systematic review of definitions and research utility.
abstract: OBJECTIVE
  Despite the common use of contagion to analogize the spread of suicide, there is a lack of rigorous assessment of the underlying concept or theory supporting the use of this term. The present study aims to examine the varied definitions and potential utility of the term contagion in suicide-related research.
  
  
  METHODS
  100 initial records and 240 reference records in English were identified as relevant with our research objectives, through systematic literature screening. We then conducted narrative syntheses of various definitions and assessed their potential value for generating new research.
  
  
  RESULTS
  20.3% of the 340 records used contagion as equivalent to clustering (contagion-as-cluster); 68.5% used it to refer to various, often related mechanisms underlying the clustering phenomenon (contagion-as-mechanism); and 11.2% without clear definition. Under the category of contagion-as-mechanism, four mechanisms have been proposed to explain how suicide clusters occurred: transmission (contagion-as-transmission), imitation (contagion-as-imitation), contextual influence (contagion-as-context), and affiliation (contagion-as-affiliation). Contagion-as-cluster both confounds and constrains inquiry into suicide clustering by blending proposed mechanism with the phenomenon to be studied. Contagion-as-transmission is, in essence, a double or internally redundant metaphor. Contagion-as-affiliation and contagion-as-context involve mechanisms that are common mechanisms that often occur independently of apparent contagion, or may serve as a facilitating background. When used indiscriminately, these terms may create research blind spots. Contagion-as-imitation combines perspectives from psychology, sociology, and public health research and provides the greatest heuristic utility for examining whether and how suicide and suicidal behaviors may spread among persons at both individual and population levels.
  
  
  CONCLUSIONS
  Clarifying the concept of "suicide contagion" is an essential step for more thoroughly investigating its mechanisms. Developing a clearer understanding of the apparent spread of suicide-promoting influences can, in turn, offer insights necessary to build the scientific foundation for prevention and intervention strategies that can be applied at both individual and community levels.
authors.affiliation: HKJC Centre for Suicide Research and Prevention, The University of Hong Kong, Hong Kong SAR, and Department of Psychiatry, University of Rochester Medical Center, Rochester, New York, United States of America.
authors.forename: Qijin
authors.initials: Q
authors.lastname: Cheng
authors.affiliation: School of Management, University of Chinese Academy of Sciences, Beijing, China, and Department of Psychiatry, University of Rochester Medical Center, Rochester, New York, United States of America.
authors.forename: Hong
authors.initials: H
authors.lastname: Li
authors.affiliation: Injury Control Research Center for Suicide Prevention and Department of Psychiatry, University of Rochester Medical Center, Rochester, New York, United States of America.
authors.forename: Vincent
authors.initials: V
authors.lastname: Silenzio
authors.affiliation: Injury Control Research Center for Suicide Prevention and Department of Psychiatry, University of Rochester Medical Center, Rochester, New York, United States of America; VA Center of Excellence for Suicide Prevention, Canandaigua, New York, United States of America.
authors.forename: Eric D
authors.initials: ED
authors.lastname: Caine
mesh_terms: D006801:Humans; D007100:Imitative Behavior / Q000502:physiology*; D012106:Research; D013405:Suicide / Q000523:psychology*; D013406:Suicide, Attempted / Q000523:psychology*