Event-Based Surveillance in mass gatherings: a global scoping review on effectiveness, scope, and lessons learned.

Introduction: Mass gatherings (MGs) attract large populations in specific places and times ranging from religious pilgrimages and cultural festivals to international sporting events. These events can drive rapid disease transmission, cross-border spread, and strain health systems requiring robust surveillance systems to detect health threats in real time. Event-Based Surveillance (EBS) offers a proactive approach to detecting such threats through systematic detection of signals. The aim of this scoping review is to assess global experiences of EBS during MGs focusing on geographical distribution, effectiveness, strategies, scope, and identifying lessons learned. Methods: A scoping review was conducted using PRISMA-ScR 2018 checklist and the Population, Concept, Context framework. All study types without time limits were included. Searches in PubMed, Scopus, ProQuest, and gray literature from WHO and CDC were screened. Two independent reviewers screened titles, abstracts and full texts then extracted data on study characteristics, surveillance design, scope, and outcomes. Results: From 1,469 publications, 28 were included where sportive events represented 39%, religious events represented 21%, cultural and political events 7% and others (33%) covered mixed or all MGs types. Publications included 50% peer-reviewed studies, 43% gray literature and 7% theses. EBS was reported effective in 75% of studies, partially effective in 11% and unspecified in 4 (14%) with one study highlighting evaluation gaps. Most publications (64%) integrated EBS with indicator-based and/or other surveillance while 36% applied standalone EBS. Scope was infectious-disease focused in 50% of studies with fewer all-hazard applications (39%) and 11% addressed specific areas such as bioterrorism. Multisectoral collaboration was the main best practice (46%) and coordination gaps represented the leading challenge (29%). Discussion: The included literature frequently describes EBS in MGs as effective, but the evidence base is limited and standardized evaluation criteria is needed. EBS in MGs is generally effective but under-represented in research. Future priorities include strong multisectoral collaboration, integrated surveillance systems, EBS evaluation platforms development and all-hazard coverage to ensure timely detection and preparedness for international mass gatherings.