Epidemiological surveillance and infectious disease outbreaks during mass international summertime sports gatherings: A narrative review

Our work on mass gatherings started in 2021 with the Santé publique France team in Île-de-France looking into all of the risks that have been described during different 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 ahead of the Paris 2024 Olympic and Paralympic Games. It was updated in 2023 in liaison with Santé publique France’s Infectious Diseases Department in order to target the specific infection risks associated with mass sports gatherings held in summertime. The aim was to better identify the challenges involved with the Paris 2024 Olympic and Paralympic Games.

This exhaustive review confirms that cases of infectious diseases have clearly been described during mass summertime sports gatherings. This makes perfect sense since, even when there are no mass gatherings, outbreaks happen every summer: food poisoning, viruses, legionellosis, meningitis and, more recently*, several indigenous cases of arboviruses (dengue and chikungunya). However, this report also confirms that all of the epidemics recorded were already established before the gatherings began. Examples of this include the Zika virus during the Rio 2016 Olympic and Paralympic Games, meningitis and measles during the 2010 Football World Cup in South Africa, and COVID-19 during the UEFA Cup in the UK and Italy in 2020. Basically, cases do occur during mass summertime sports gatherings, but they do not present a major public health risk for 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, which can potentially lead to epidemics. It is important to emphasise 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 circulation of pathogens or to the risk of epidemics in a given area and 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 lead to difficulties for the regional health agencies in terms of managing cases and for Santé publique France when interpreting the indicators. That is why it is important to document the number of people present in real time in a given place and at a given site as accurately as possible. Telephony data, for example, which are already used in France for modelling purposes, could be collected. Having access to these detailed data mean 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 seen during peaks of hot weather or persistent heat episodes, and of course in the event of a heatwave. This happened 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 set up throughout mainland France after the summer of 2023 and is coordinated by Santé publique France in conjunction with the French weather service, Météo-France. It is active between 1 June and 30 September. The system is designed to measure the health impact of heat on the population and to support the authorities in their decision-making process. 

Santé publique France has many years of experience with mass gatherings (Turin 2006, D-Day celebrations in 2014, COP21 in 2015 in Île-de-France, Rouen Armada 2023, etc.). The agency’s experience in this domain will continue to develop, taking its lead from epidemiological requirements. The teams at Santé publique France were able to trial a surveillance system during the Rugby World Cup 2023 and test certain indicators** during the Rouen Armada. 

The main lesson to be learnt from carrying out 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 mobilised for these events on top of their existing activities within the agency. 

France counts 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 or the identification of unusual health signals. The 2024 Olympic Games have presented 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 adjoining departments of Hauts-de-Seine, Seine-Saint-Denis and Val-de-Marne). We are publishing data from these surveillance systems every week 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 putting a strain on the public health system. Whatever the context, these need to be investigated and refuted or confirmed in order to determine whether there is a health risk, which takes time.