Title Suicide contagion : A systematic review of definitions andresearch utility

Objectives: 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. Conclusion: 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. Citation: Cheng Q, Li H, Silenzio V, Caine ED (2014) Suicide Contagion: A Systematic Review of Definitions and Research Utility. PLoS ONE 9(9): e108724. doi:10. 1371/journal.pone. 0108724 Editor: Martin Voracek, University of Vienna, Austria Received June 10, 2014; Accepted September 3, 2014; Published September 26, 2014 Copyright: 2014 Cheng et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: The authors confirm that all data underlying the findings are fully available without restriction. All relevant data are within the paper. Funding: QC, HL, and EDC were supported, in part, by a grant from the US National Institutes of Health Fogarty International Center, D43 TW009101. VS and EDC were supported, in part, by the US Centers for Disease Control and Prevention grant R49 CE002093. In addition, QC was supported by The University of Hong Kong; HL was supported by the University of the Chinese Academy of Sciences; and VS and EDC also were supported by funds from the University of Rochester Medical Center. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * Email: chengq@hku.hk