Respiratory tract infections such as influenza and measles are the most common infections in major sporting events. In the 2018 Winter Olympics, Team Finland reported that respiratory tract infections caused by coronaviruses, influenza B virus, respiratory syncytial virus A, rhinovirus, and human metapneumovirus affected 45% of the athletes and 32% of staff members of the service team [28]. Measles is also a highly infectious and acute viral respiratory tract infection that caused small outbreaks in sports events such as the 1991 International Special Olympics Games, 1991 International Gymnastics Competition, and 2007 International Youth Sporting Event [7]. At the end of 2019, the sudden outbreak of COVID-19 disrupted the pace of human life, and many sports events were forced to be cancelled or postponed. Thailand first reported SARS-CoV-2 transmission in a boxing sport stadium, with 27 individuals infected [29]. During the Tokyo Olympics and Paralympics, the positive rates of COVID-19 tests were 0.10% and 0.03% for games-related people arriving at airports and people living in the Tokyo 2020 bubble, respectively, including 24 of 11,476 Olympic athletes and 13 of 4303 Paralympic athletes who tested positive [30]. As for the Beijing 2022 Winter Olympics and Paralympics, 284 of the 16,092 games-related people tested positive at the airport and 179 people tested positive in the closed loop with no cluster epidemic [31] (see Tables S1 and S2 of Multimedia Appendix 1).

Risk factors for respiratory infectious diseases have mainly included three aspects. First, respiratory tract infections could easily be transmitted in confined places; therefore, ventilation conditions, temperature, cold, and dry air in the competition grounds were highlighted as risk factors for respiratory tract infections, because these conditions are suitable for viruses to survive and colonize the human respiratory tract [8]. Second, individuals with routine exposure to international travelers might be at greater risk of respiratory tract infections [32]. Third, people with chronic diseases or weak immunity are more susceptible to respiratory tract infection, as well as its aggravation or complications [32] (Figure 4).

For the ongoing COVID-19 epidemic, the emerging viral variants and the relatively low vaccination rate brought challenges to the holding of major sports events [33]. When holding the Tokyo Olympics, only 3.4% of the population in Japan had been immunized [33]. Another risk for the spread of COVID-19 is the uncontrolled gathering for activities occurring outside the venue during the sports events. Two studies indicated that the increase in COVID-19 cases and cluster epidemics during the 2020 European Football Championship (EURO) were more likely to occur as a result of aggregations and celebrations in private settings, pubs/other public buildings, or public squares rather than from the official football events [34,35]. In addition, previous studies found that athletes had a higher risk of COVID-19 than staff members during professional football competitions [36,37] (Figure 4).

Norovirus and Salmonella were the main pathogens that caused gastrointestinal infections in major sports events. In the 2015 Obstacle Adventure race, 866 of 1264 adults reported acute gastroenteritis infections [38]. In the 2018 PyeongChang Winter Olympics, symptoms associated with the gastrointestinal tract, including diarrhea, vomiting, and dyspepsia, were the second most common reported [10]; an outbreak of norovirus infections was recognized, starting with security staff, and noroviruses were detected in samples from food handlers [39] (Multimedia Appendix 1 Tables S1 and S2).

Dirty floors and bathrooms, contaminated food and unhygienic cooking, and serving staff with little awareness of hygiene were all highlighted as risk factors for gastrointestinal infections [38]. Younger athletes (aged 18-27 years) had a significantly higher risk of acute gastrointestinal infection [38]. Ingestion of mud during sports events was associated with gastrointestinal infection [38]. In addition, the pathogens could be transmitted by sharing water bottles or food boxes [40] (Figure 4).

During the 2014 FIFA World Cup and the 2016 Rio Olympics Games, vector-borne diseases such as Zika and dengue aroused wide public concern. Due to the efforts of implementing highly effective preventive measures against vectors, there were no epidemic incidents during either event in Brazil [41,42] (Multimedia Appendix 1 Tables S1 and S2).

The primary vectors of Zika, Aedes mosquitoes, breed larvae in standing water. Potential mosquito breeding sites (eg, tires, flowerpots, buckets, and other similar containers) were highlighted as risk factors for disease spread [43]. In addition, temperature, precipitation, and other environmental factors had an impact on vector-borne disease infections [44,45] (Figure 4).

There was no statistically significant increase in clinic attendance for blood-borne infections (eg, HIV, hepatitis B virus, or hepatitis C virus infections) during sports events in previous years. Sexual transmission was the main transmission route for such infections. The distribution of condoms and health-related messages about safer sex might have contributed to the successful control of blood-borne infections during major sports events [46-48] (Multimedia Appendix 1 Tables S1 and S2).

Injuries and close contacts during competition were highlighted as risk factors for blood-borne pathogen transmission. The pathogen could transmit through bleeding wounds or exudative skin lesions of an infected athlete to the injured skin or mucous membrane of another athlete [12]. Migration was also an important risk factor. Internal and international migration of commercial sex workers might become an important vector for the transmission of HIV [3] (Figure 4).

The largest outbreak of leptospirosis was reported in the 1998 Springfield triathlon, held in the United States. Among 834 athletes in the Springfield triathlon, 98 (11.8%) met the definition for a suspected case [11] (Multimedia Appendix 1 Tables S1 and S2). Heavy rains that preceded the triathlon were likely to cause leptospiral contamination of the lake. Urine from small mammals (eg, rodents such as mice and rats), wild boars, or domestic pigs was proposed as a possible source of Leptospira. Swimming or wading in fresh unchlorinated water containing contaminated animal urine was another potential cause of leptospirosis [11,49,50] (Figure 4).

Vaccination emerged as the most effective preventive measure. All delegation members, staff, volunteers, and accompanying visitors should be appropriately vaccinated according to the recommendations of their respective nations before arrival [51,52]. Under the influence of a global pandemic of infectious diseases, local and state health departments should work quickly with organizing committees and governing bodies to establish plans for evaluation, treatment, and prophylaxis, and to ensure that vaccination clinics are functioning appropriately [51] (Figure 4, Multimedia Appendix 1 Tables S1 and S2).

The strategy for respiratory tract infections prevention can integrate empiric treatment based on clinical data and viral testing, along with a public health surveillance approach, including daily review of all viral test results from the polyclinic and reports of symptoms in the community [8]. Nonpharmacological interventions such as social distancing, facemask wearing, and ventilation efficiency enhanced in the stadium are also needed to minimize the risk of community transmission [53,54] (Figure 4, Multimedia Appendix 1 Tables S1 and S2). To prevent COVID-19 transmission, no spectators were allowed and a bubble scheme for games-related people was implemented in some international sports events represented by the Tokyo Olympics and Paralympics, which consisted of a series of measures that separated participants from the general public [55]. Such a closed-loop management strategy was also implemented in the Beijing Winter Olympics and Paralympics [56]. Another strengthening preventive measure was frequent SARS-CoV-2 testing. During the Tokyo Olympics and Paralympics, all participants had to undergo laboratory-based saliva antigen screening every day, and relevant isolation and close-contacts management were implemented for people with positive nucleic acid testing results [30,55]. In addition, it is strongly recommended that games-related people should be vaccinated against COVID-19. More than 80% of athletes and staff were vaccinated in the Tokyo Olympics and Paralympics [55].

For gastroenteritis infections, standard hand hygiene and food safety precautions were recommended, such as eating appropriately cooked food and drinking bottled beverages. Participants were also advised to notify medical offices if gastrointestinal symptoms appeared during or after the competition [23]. In the meantime, the awareness and education of the public as well as of health care professionals are warranted [57] (Figure 4, Multimedia Appendix 1 Tables S1 and S2).

The mainstay for vector-borne infections prevention is to avoid mosquito bites [43,58]. Participants must take extra care to follow recommendations from the sports event organizing committee for insect repellant and clothing treatment [59]. Some equipment was recommended, including rooms with air conditioning, window and door screens, mosquito bed nets, and official registered insect repellents, which are proven to be safe and effective [43] (Figure 4, Multimedia Appendix 1 Tables S1 and S2).

Emphasis on the prevention of transmission of blood-borne pathogens in athletes should focus on reducing the traditional modes of transmission and modification of off-the-field behavior, including the avoidance of unprotected high-risk sexual activity and needle sharing in the use of illicit drugs such as anabolic steroids or blood doping [60,61]. Athletes should also practice good personal hygiene and not share personal items that might be contaminated with blood, such as razors, toothbrushes, and nail clippers [60,61]. In addition, education regarding universal precautions when dealing with blood or body fluids should also be enhanced [60,61] (Figure 4, Multimedia Appendix 1 Tables S1 and S2).

To prevent water-contact infections in eco-challenge and racing competitions, racers and organizers should be aware of the potential risk of inadvertent ingestion of muddy and possibly contaminated water during the race [62]. In general, planners of these competitions should consider building circuits to avoid areas heavily contaminated with animal feces [62]. In addition, clean running water should be available at stations to allow racers to clean mud off their hands and faces prior to eating and drinking [57]. An alternate form of water delivery should also be considered, such as bottles of water, which are less easily contaminated than paper cups [57]. It is also recommended that bike racers use front and rear fenders to reduce splashing of mud onto their and other riders’ faces, respectively [57] (Figure 4, Multimedia Appendix 1 Tables S1 and S2).

Before the 1990s, major sports events mainly used traditional methods for disease surveillance. Traditional disease surveillance relied on routine manual filing of reportable diseases by clinicians [16-21]. With the continuous development of information technology, infectious disease surveillance technology in major sports events has gone through three stages of development.

The first generation of a complete disease surveillance network for major sports events was applied in the 1984 Los Angeles Olympic Games. The whole network covered 46 hospitals, 90 physician offices, 4 university student health centers, 31 preschools, 3 Olympic Village polyclinics, and 24 Olympic first-aid stations [63]. During the Games, the International Olympic Committee made three phone calls per week with 198 participating sites. Each site used a disease report card to report disease information [63]. Early active surveillance systems reported structured and simple data, mainly including the name of surveillance sites, type of surveillance sites, date, and number of cases (grouped by disease type and age of patients) [64-66] (Figure 5).

After 1995, the second generation of surveillance networks emerged with extensive application of internet technology in infectious disease surveillance that enhanced existing systems and integrated multisource data with richer data types that significantly improved real-time performance. During the 1996 Atlanta Olympic Games, the government designed and implemented “outside the fence” and “inside the fence” surveillance systems. The “outside the fence” system was an augmented surveillance system implemented for health conditions that occurred outside of Olympic venues, while the “inside the fence” surveillance system was established to enumerate clinical encounters in Olympic venues and at contract hospitals for Olympic athletes, official Olympic staff, and national delegations [67]. Continuous surveillance data collection allowed uninterrupted monitoring of disease epidemic trends.

In the following major sports events (eg, 2000 Sydney Olympics, 2006 Germany FIFA World Cup, 2007 International Cricket World Cup, 2008 EURO, 2008 Beijing Olympics), the infectious disease surveillance system continued using this mode, with two major improvements, including enhancing the existing domestic surveillance system and establishing syndromic surveillance targeting health-related symptoms [4-6,68,69]. Data structures and types were enriched in the form of electronic medical records. Automatic data acquisition technology improved the timeliness of information collection and reporting. Complex algorithms and models were used to predict outbreaks of infectious diseases. Several professional global surveillance networks (eg, GeoSentinel, Healthmap) were set up, collecting clinician-based sentinel surveillance data (diagnosis, travel itinerary, demographics) to support the prevention and control of infectious diseases in major sports events [22,70].

After 2016, mobile internet apps and artificial intelligence algorithms were applied to monitor participants’ health status in sports events. In the 2016 Rio Olympics, a surveillance platform based on a mobile app was installed on participants’ smartphones called “OlymTRIP,” which monitored health status through a daily interactive check of user health status, including geolocalization data [71]. The app also provided information and advice about Zika infection. In case of feeling unwell, participants could contact doctors through the app, and doctors could also track the health status of the participants in a real-time manner using a web-based platform.

In addition to mobile phones, there are many types of wearable devices for infectious disease monitoring. Using an agent-based model, the data collected by wearable devices were applied to explore the feasibility of using tracking data from a football match to assess interpersonal contact between individuals by calculating two measures of respiratory exposure [72]. More multisource data and more advanced technologies were integrated into the monitoring system, including online public opinion monitoring based on natural language processing technology, risk classification monitoring of international passengers based on global aviation data, and the risk early warning model of infectious diseases [22,24,73]. In addition, enhanced event-based surveillance was undertaken by the National Institute of Infectious Diseases, Japan, to identify infectious diseases occurring overseas (excluding COVID-19) that had potential for importation during the Tokyo Olympics [74].

In response to the challenges of COVID-19, some surveillance measures focusing on COVID-19 were developed and implemented. The COVID-19 athlete passport system was used during the Tokyo Olympic games to present a novel way of managing athletes’ previous exposure, testing results, and vaccination status, which could be used to tailor appropriate precautions to each athlete [75]. A large-scale COVID-19 monitoring program involving daily testing was instituted during the US 2020 National Football League season [76]. For enhanced surveillance activities during EURO 2020, a specific identifier was marked in the system for each case within the observation period that might have had an association with the games to facilitate communication and timely case detection by local health authorities [77]. In addition, some image-based technologies of mask-wearing detection could contribute to monitoring the athletes’ and spectators’ mask-wearing behaviors during sports events [78] (Figure 5).