Health surveillance at mass gatherings: experience report from the Strategic Health Surveillance Information Center in the city of Rio de Janeiro, 2024.

Objective: To describe the health surveillance strategy implemented at mass gatherings by the Strategic Health Surveillance Information Center of the Rio de Janeiro Municipal Health Department, focusing on its activities at a music festival.

Methods: This is an experience report. The music festival, which took place in 2024, was attended by 730,000 people. Before the event, operational preparations were carried out, and the local, national, and international epidemiological scenarios were monitored using digital detection tools. During the event, on-site actions were carried out, and active searches were conducted for cases of notifiable diseases/conditions and events of public health interest. During and after the event, local epidemiological surveillance was maintained to identify any potential changes associated with the festival.

Results: Pre-event monitoring identified an increase in cases of whooping cough, outbreaks of diarrheal diseases, and the occurrence of measles, Oropouche virus, and avian influenza. During the event, 243 cases of notifiable diseases or conditions were reported, particularly influenza-like illness (42.0%) and exogenous intoxication (32.9%), as well as two outbreaks of exogenous intoxication and one outbreak of diarrheal disease. No changes were observed in the epidemiological scenario of the city of Rio de Janeiro following the event.

Conclusion: The health surveillance response encompassed a comprehensive set of actions before, during, and after the event, enabling appropriate preparedness, early detection, and rapid response to potential public health emergencies. The lessons learned from this mass gathering will be incorporated into the planning and preparedness for future events.