Tailoring event-based surveillance using open sources: practical guide for mass gatherings

Public health intelligence (PHI) is key to early warning alert and response (EWAR), and is vital in protecting the health of the populations in the context of mass gatherings (MGs). PHI allows rapid identification, collection, synthesis, analysis, assessment, interpretation and generation of a wide range of information. This information, including event-based surveillance (EBS), enables actionable insights and their dissemination for informed decision-making. This practical guide describes the steps required to implement EBS for an MG using open sources, together with case studies from past MGs, primarily focusing on supporting national surveillance focal points.