Mass-gatherings events provide a difficult setting for which to plan an appropriate emergency medical response. Many of the variables that affect the level and types of medical needs, have not been fully researched. This review examines these variables.Methods:An extensive review was conducted using the computerized databases Medline and Healthstar from 1977 through May 2002. Articles selected contained information pertaining to mass-gathering variables. These articles were read, abstracted, analyzed, and compiled.Results:Multiple variables are present during a mass gathering, and they interact in complex and dynamic ways. The interaction of these variables contributes to the number of patients treated at an event (medical usage rate) as well as the observed injury patterns. Important variables include weather, event type, event duration, age, crowd mood and density, attendance, and alcohol and drug use.Conclusions:Developing an understanding of the variables associated with mass gatherings should be the first step for event planners. After these variables are considered, a thorough needs analysis can be performed and resource allocation can be based on objective data.

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