Included Studies Characteristics

Following the search, a total of 745 publications were identified from the Web of Science, Scopus, Cochrane, and PubMed databases. After eliminating duplicate articles, 567 publications remained. Among these, the abstracts of 440 studies did not meet the inclusion criteria, and the full texts were not reviewed. The full texts of the remaining 127 studies were read, and 72 of them were excluded. Of these, 61 of them were not relevant, eight were of low quality, the full text of two could not be accessed, and one was not in English. As a result, 55 articles were included in the study findings (Figure 1). The publication dates of the 55 studies included in the research findings ranged from 1990 through 2023. Among them, 45 were original research, three were special reports, three were case reports, two were brief reports, one was a short paper, and one was a report from the field (Table 1 ^{Reference Alassaf13–Reference Zeitz, Haghighi and Burstein67} ).

Figure 1. Flow Diagram of Study Identification and Selection Process.

Table 1. Characteristics of the Included Articles

Abbreviations: ATR, ambulance transfer rate; EHP, event-to-host-population ratio; In-PPR, intra-venue PPR; MARR, mutual aid request rate; METH, medical center to hospital; MG, mass gathering; MTR, medical transfer rate; MUR, medical usage rate; OHCA, out-of-hospital cardiac arrest; Out-PPR, out-of-venue PPR; PDR, pre-diagnosis rate; PPR, patient presentation rate; RTHR, referrals-to-hospital rate; TTHR, transport-to-hospital rate; USFMP, using start-finish medical post; VAR, venue accommodation rate.

Descriptive Analysis of Documents

As a result of the systematic review, a total of 15 metrics were obtained, including event-to-host-population ratio (EHP), venue accommodation rate (VAR), injury/season injury rate, rates of out-of-hospital cardiac arrest (OHCA), pre-diagnosis rate (PDR), attack rate, patient presentation rate (PPR), rate of using Start-Finish Medical Post (USFMP), MUR, ambulance transfer rate (ATR), medical service to hospital (METH), mutual aid request rate (MARR), transfer-to-hospital rate (TTHR), referral-to-hospital rate (RTHR), and medical transfer rate (MTR). These 15 metrics have been categorized into three groups: assessment of population density, in-event health services, and out-of-event health services. The formulas for the rate and ratios used in mass gatherings are presented in Table 2, and detailed information regarding these metrics is elaborated below.

Table 2. Formulas for the Metrics Used in Mass-Gathering Events

Abbreviations: ATR, ambulance transfer rate; EHP, event-to-host-population ratio; In-PPR, intra-venue PPR; MARR, mutual aid request rate; METH, medical center to hospital; MTR, medical transfer rate; MUR, medical usage rate; OHCA, out-of-hospital cardiac arrest; Out-PPR, out-of-venue PPR; PDR, pre-diagnosis rate; PPR, patient presentation rate; RTHR, referral-to-hospital rate; TTHR, transport-to-hospital rate; USFMP, using start-finish medical post; VAR, venue accommodation rate.

Assessment of Population Density

Event-to-Host-Population Ratio (EHP)—The EHP ratio refers to the ratio of the number of attendees in a mass-gathering event to the host population during the event. ^{Reference Spaepen, Haenen and Kaufman54} Derived by dividing attendees by the host population, it guides resource planning, aiding organizers in ensuring event success without overwhelming infrastructure. Additionally, the EHP ratio anticipates health care demand, serving as a proactive tool for preparedness.

Venue Accommodation Rate (VAR)—The crowd density affects the volume of patients treated at an event, and the VAR serves as an indicator of this density. ^{Reference Milsten, Maguire and Bissell7} It is defined as the rate of the actual number of spectators per event to the maximum capacity for attendees, expressed as a percentage. ^{Reference Morimura, Katsumi and Koido47} A high rate suggests that the actual number of attendees per event is approaching or exceeding the maximum capacity, indicating a densely populated venue. On the other hand, a low rate suggests that there is still considerable capacity available in the venue, indicating a lower crowd density.

Assessment of In-Event Health Services

Injury Rate/Season Injury Rate—The injury rate is a metric that measures the frequency of injuries in a specific population or context and is commonly reported in mass-gathering events. The calculation of the injury rate involves dividing the total number of injuries by the overall number of attendees, typically presenting the result as a percentage. In addition, the season injury rate illustrates the cumulative injury rate occurring over one year, obtained by dividing the total injury rates within a year by 12 months. ^{Reference Rabb and Coleby51} A higher injury rate indicates a greater frequency of injuries relative to the population or exposure, while a lower rate suggests a lower incidence of injuries.

Rate of Out-of-Hospital Cardiac Arrest (OHCA)—While OHCA is not a metric specific to mass gatherings, it signifies the unexpected cessation of an individual’s heart activity, typically occurring outside the hospital. The OHCA rate is calculated by dividing the number of OHCA cases during the event by the total number of attendees and then multiplying the result by a factor, often expressed per 100,000 attendees. ^{Reference Goldberg, Battistini and Cash29} Even though not explicitly stated as OHCA in the literature, there are also studies providing the incidence rate of cardiopulmonary arrest per 10,000 attendees. ^{Reference Bock, Cordell and Hawk18,Reference Tajima, Takazawa and Yamada59} A high OHCA rate or incidence rate of cardiopulmonary arrest in mass-gathering events suggests a high demand for emergency medical interventions and services such as responding to heart attacks. On the other hand, a low rate suggests a lower demand for emergency health care services during the event, and organizers may require fewer emergency resources.

Pre-Diagnosis Rate (PDR)—Injuries and illnesses like trauma, acute gastroenteritis, headache, myalgia, and sunburn are usually presented by frequency or percentage in mass-gathering events. In the literature, a few studies have provided PDR or the incidence rates of patient diagnosis/symptoms. ^{Reference Spaite, Meislin and Valenzuela58} The PDR or rates of patient diagnosis/symptoms are employed to evaluate the incidence of specific diagnoses among patients or injured individuals. It is calculated by dividing the count of diagnoses by the total number of attendees and then multiplying the result by a factor, often expressed per 1,000 attendees. ^{Reference Koçak, Çalışkan and Sönmezler37} A high diagnosis rate suggests an increased incidence of specific conditions among attendees in mass gatherings, indicating potential health issues before a formal diagnosis. This information assists event planners, health care professionals, and public health authorities in customizing their services. On the flip side, a lower rate of diagnosis might suggest an attendee population that is generally healthier; however, factors such as the type of event, demographics, and pre-existing conditions observed should be taken into account.

Attack Rate—Attack rate is a term typically used to measure the speed of the spread of an outbreak or disease. It is calculated by dividing the total number of cases that occur during a specific period or in a specific situation by the total population, often expressed as a percentage. While not exclusive to mass gatherings, it is a crucial metric for understanding the dynamics of the spread of outbreaks and diseases, informing preventive measures, and guiding the implementation of public health strategies in mass gatherings. ^{Reference Rajakrishnan, Hafiz Ismail and Jamalulail52} It plays a significant role, particularly in the control of infectious diseases and the management of outbreak situations.

Patient Presentation Rate (PPR)—The PPR is a metric used to assess the number of patient presentations to a health care facility or service during a specific period within a mass-gathering event. In the literature, it is also observed that the PPR is analyzed in two separate categories for mass-gathering events: “Intra-venue PPR (In-PPR)” and “Out-of-venue PPR (Out-PPR).” In-PPR refers to presentations within the event venue, while Out-PPR pertains to presentations outside the venue. ^{Reference Morimura, Katsumi and Koido47} However, it is often reported as PPR in the literature. The PPR is calculated by dividing the total number of patient presentations during the event by the overall number of attendees, and the result is often multiplied by a coefficient such as 10,000 for standardized reporting. ^{Reference Arbon, Bridgewater and Smith17} A heightened PPR typically indicates a heightened demand for health care services, suggesting an escalation in health-related concerns during mass gatherings and signaling a potential necessity for emergency interventions. Conversely, a lower PPR generally signifies reduced demand for health care services, indicating that anticipated health issues during mass gatherings are limited, thereby reducing the need for emergency interventions.

Rate of Using Start-Finish Medical Post (USFMP)—Start-Finish Medical Post (SFMP) is a facility located at the start and finish lines of mass gatherings like marathons or cycling races. Its purpose is to provide prompt medical assistance to attendees facing emergencies, serving as a central hub with personnel and resources. The rate of USFMP is a metric that indicates the frequency or ratio of attendees seeking medical assistance or services at the SFMP during an event. It is calculated by dividing the number of individuals who utilize the SFMP services by the total number of attendees, often expressed per 10,000 attendees. ^{Reference Ussahgij, Kotruchin and Osotthanakorn62} Although it yields the same output as PPR, USFMP is commonly used in sports events.

Medical Usage Rate (MUR)—The MUR, as also known overall usage rate, refers to the rate of utilization or demand for medical services or resources during a mass-gathering event. ^{Reference Milsten, Maguire and Bissell7,Reference Burton, Corry and Lewis20} The MUR is calculated by dividing the number of individuals seeking medical care by the total attendance for that event and is typically reported as a rate in patients per 10,000 (PPTT). ^{Reference Hostettler-Blunier, Müller and Haltmeier34,Reference Sabra, Cabañas and Bedolla53,Reference Thierbach, Wolcke and Piepho60} The PPR also is referred to as the MUR, but PPR may be limited in some studies to presentations to medical services and exclude first aid and other prehospital care presentations. ^{Reference Arbon68} Therefore, it can be said that MUR encompasses the total patient presentations, including all presentations delivered by first aid providers and professional health care workers.

Assessment of Out-of-Event Health Services

Ambulance Transfer Rate (ATR)—The ATR typically refers to the rate of individuals at a mass-gathering event who require transportation to a health care facility via ambulance. This rate is calculated by dividing the number of individuals transferred by ambulance to a medical facility by the total number of attendees in the mass gathering, often expressed as per 1,000 attendees. ^{Reference Gutman, Lund and Turris31,Reference Lund and Turris41} The ATR is an important metric in assessing the need for Emergency Medical Services and the overall health and safety considerations during large events. It provides insights into the demand for ambulance services, the severity of incidents, and the effectiveness of medical response strategies in the context of mass gatherings.

Medical Center to Hospital (METH)—The METH metric refers to individuals who, after receiving on-site medical services at a medical center or medical station located at an event, are transferred to a hospital for further medical treatment. The rate of METH is calculated by dividing the number of individuals evacuated to the hospital by the total number of cases or individuals. ^{Reference Bortolin, Ulla and Bono19} Similar to ATR, METH provides the rate of patients transported by ambulance; however, METH is usually presented as a percentage.

Mutual Aid Request Rate (MARR)—In general terms, mutual aid refers to cooperation and assistance provided by one organization or group to another, often in emergency or challenging situations. The MARR represents the rate of mutual aid requests made during a mass gathering, and it is defined as the ratio of patients transported to the hospital by ambulance, excluding ambulances stationed on campus for the event, to every 1,000 attendees. ^{Reference Friedman, O’Connor and Munro27}

Transport-to-Hospital Rate (TTHR)—The TTHR is a metric that measures the rate at which individuals are transported to a hospital after seeking emergency services or another health care unit in mass-gathering events. It is calculated by dividing the total number of patients transported to the hospital during the event by the overall number of attendees, and the result is often multiplied by a coefficient such as 10,000 for standardized reporting. ^{Reference Arbon, Bridgewater and Smith17} Similar to METH and ATR, TTHR typically presents the rate of patients transported by ambulance and may not include patients who were transferred to the hospital using their own means. This rate, typically provided alongside PPR, is used to assess the severity of out-of-event health care services during mass-gathering events, to ensure patients’ access to appropriate treatment, and to allocate health resources effectively. ^{Reference Scheers, Van Remoortel and Lauwers69} A high TTHR may indicate increased out-of-event health care services needs and more serious patient conditions in mass gatherings, implying a higher demand for emergency medical intervention. Conversely, a low TTHR suggests milder health issues and lower demand for out-of-event health care services.

Referral-to-Hospital Rate (RTHR)—Transport generally refers to the conveyance of an individual to a health care facility, typically facilitated by an ambulance. The TTHR specifically encompasses referrals to the hospital through ambulances, and it indicates how many individuals were transported to the hospital via ambulances during a mass-gathering event. Referral, on the other hand, signifies directing an individual to a more specialized health care unit or a specialized doctor, and it encompasses all methods. This includes individuals referred to the hospital by health care professionals, ambulance, or different methods. ^{Reference Ranse and Hutton70} In this context, RTHR measures the frequency of individuals being referred to specialized health care services during mass gatherings, indicating the likelihood of referral based on incident severity. The calculation involves dividing the total hospital-referred patients by the overall attendee count during the event, and the outcome is frequently scaled by a coefficient like 10,000 for standardized reporting. ^{Reference Crabtree, Mo and Ong24}

Medical Transfer Rate (MTR)—The ATR specifically pertains to the frequency of emergency ambulance responses and transfers, specifically related to emergency calls, throughout the event. On the other hand, MTR comprises all external referrals, encompassing ambulance transfers and other forms of medical transportation. ^{Reference Gutman, Lund and Turris31} To elaborate, the ATR is narrowly focused on the occurrence of emergency ambulance responses and subsequent transfers, whereas the MTR encompasses a broader spectrum of medical transfers, accounting for various modes of transportation that may not necessarily involve public ambulance services. In short, it can be said that it produces the same output as RTHR and encompasses all total referrals.