Our work on mass gatherings began in 2021, when the Santé publique France team in Île-de-France examined all the risks that have been identified in various types of mass gatherings. This literature review was shared with partners and health authorities in early 2022 as a contribution to the risk mapping process leading up to the Paris 2024 Olympic and Paralympic Games. It was updated in 2023 in collaboration with Santé publique France’s Department of Infectious Diseases to address the specific infection risks associated with mass summer sports gatherings. The goal was to better identify the challenges associated with the Paris 2024 Olympic and Paralympic Games.

This comprehensive review confirms that cases of infectious diseases have clearly been documented during large-scale summer sports gatherings. This is entirely expected, since outbreaks occur every summer even in the absence of such gatherings: food poisoning, viruses, Legionnaires’ disease, meningitis, and, more recently*, several locally transmitted cases of arboviruses (dengue and chikungunya). However, this report also confirms that all of the recorded epidemics were already established before the events began. Examples include the Zika virus during the 2016 Rio Olympic and Paralympic Games, meningitis and measles during the 2010 FIFA World Cup in South Africa, and COVID-19 during the UEFA Cup in the UK and Italy in 2020. Basically, cases do occur during large-scale summer sporting events, but they do not pose a major public health risk to athletes, spectators, or the general public. This is especially true in cities that already welcome millions of tourists every year, such as Paris.

The published review focused solely on the risks of infectious diseases that could potentially lead to epidemics. It is important to emphasize that spectators are present in the stadiums and around the perimeter of the Games for relatively brief periods, shorter than the incubation periods of most pathogens. This means that there is not enough time for these people to make any significant contribution to the spread of pathogens or to the risk of epidemics in a given area over a specific period. Therefore, it is advisable to be prepared for the usual summer infection risks listed above, even though the increased number of visitors may create challenges for regional health agencies in managing cases and for Santé publique France in interpreting the indicators. That is why it is important to document the number of people present in real time at a given location and site as accurately as possible. Telephony data, for example, which are already used in France for modeling purposes, could be collected. Having access to these detailed data means that we have a clearer picture of the number of people present (known as population denominators) when assessing the data or risks.

Some of the other health risks worth mentioning, which were identified during the initial review in 2021 (unpublished), are those observed during peaks of hot weather or prolonged heat episodes, and of course in the event of a heatwave. This occurred during the Olympic Games in Atlanta in 1996 and in Tokyo in 2021. These phenomena, which are becoming increasingly common in summer, even at our latitudes, can have a rapid and massive impact on athletes, spectators, and the general population.

The Heat Warning System (SACS) was established throughout mainland France following the summer of 2023 and is coordinated by Santé publique France in collaboration with the French meteorological service, Météo-France. It is active from June 1 through September 30. The system is designed to assess the health impact of heat on the population and to support authorities in their decision-making process.

Santé publique France has many years of experience with large-scale events (Turin 2006, the D-Day celebrations in 2014, COP21 in 2015 in Île-de-France, the Rouen Armada 2023, etc.). The agency’s expertise in this area will continue to grow, guided by epidemiological needs. The teams at Santé publique France were able to trial a surveillance system during the 2023 Rugby World Cup and test certain indicators** during the Rouen Armada.

The main lesson to be learned from conducting surveillance during these recent mass gatherings, which required significant involvement from our teams, is the importance of anticipating how much manpower is needed. This is because staff are mobilized for these events in addition to their existing duties within the agency.

France has a large number of professionals involved in health surveillance, whether for dedicated systems or day-to-day monitoring. Examples include the syndromic surveillance system SurSaUD®, the mandatory reporting of notifiable diseases, and the identification of unusual health signals. The 2024 Olympic Games have provided an opportunity to introduce new surveillance systems in conjunction with Paris 2024, based on data from the Paris Fire Brigade (BSPP) and first-aid providers around the stadiums. Surveillance data from the BSPP include the reasons for emergency calls and the number of patients treated (in Paris and the neighboring departments of Hauts-de-Seine, Seine-Saint-Denis, and Val-de-Marne). We are publishing data from these surveillance systems weekly throughout the Paris 2024 Olympic and Paralympic Games in the form of a regional health surveillance bulletin. We will need to assess how these new systems have performed before deciding whether or not to make them permanent. Santé publique France also coordinates the wastewater microbiological surveillance system (SUM'EAU), and it recently carried out a study to identify pathogens of interest for wastewater surveillance in the run-up to the 2024 Olympic Games. (See box – Wastewater surveillance during mass gatherings).

The other lesson for health surveillance during mass gatherings is that small numbers of cases will inevitably occur and be reported, without necessarily straining the public health system. Whatever the context, these cases need to be investigated and either ruled out or confirmed in order to determine whether there is a health risk, which takes time.