World Health Organization · 2026 · 118 pages
Evidence-based approaches to protect millions of attendees from extreme heat at religious pilgrimages, sporting events and festivals worldwide
- Issuer
- World Health Organization
- Edition
- 2026
- Audience
- Governments and organizations hosting mass gatherings; decision-makers at international, national, regional and municipal levels; public health professionals; event medical planners; community health workers
- Evidence
- Systematic reviews with ROBINS-I and PROBAST risk-of-bias assessment; narrative synthesis following SWiM guidelines; 54 studies included across three reviews
- Reviewed
- 17 Oct 2026 · GMJ
What this guideline says
GMJ summary
This WHO report synthesizes three systematic reviews of 54 studies covering mass gatherings with over 70 million attendees between 1978 and 2024. It provides the first comprehensive evidence base on preventing and managing heat-related illness (HRI) in high-density event settings, documenting nearly 500,000 clinical encounters including more than 22,000 cases of HRI and 1,196 heat-related deaths across religious pilgrimages, sporting events, music festivals and international exhibitions.
The findings demonstrate that effective heat stress management requires integrated, layered interventions across three domains: robust on-site medical infrastructure (capable of managing 92% of patients without hospital transfer), environmental modifications including cooling zones and hydration stations, and culturally tailored risk communication. However, critical gaps persist: no studies demonstrated formal pre-event vulnerability screening, and while digital surveillance and wearable sensor technologies show promise, most remain in pilot stages without operational integration into crowd-safety protocols.
The report identifies that HRI burden differs markedly by event type. Religious gatherings involving older populations with chronic disease showed severe morbidity and mortality (the 1985 Hajj alone accounted for 1,000+ deaths), while sporting events and music festivals involved younger crowds with lower mortality but significant HRI compounded by trauma and substance use. A persistent knowledge–action gap was documented: attendees understood heat risks but frequently failed to change behaviour, particularly at religious mass gatherings where ritual obligations superseded health advice.
Key points
For clinicians — doses and thresholds as stated in the guideline
- On-site medical infrastructure with emergency physicians enabled 92% of 443,105 patients to be managed and discharged without hospital transfer across all events studied
- Heat-related illness accounted for 22,197 cases (4.6% of all medical encounters), including 2,671 cases of heatstroke and 18,733 cases of heat exhaustion, syncope or dehydration
- Religious mass gatherings showed highest risk: older populations (mean age 47–63 years) with hypertension (up to 61.6%), diabetes (up to 47.7%) and cardiovascular disease (up to 14.4%) experienced severe HRI and 1,196 deaths
- Environmental modifications (cooling shelters, misting systems, free water distribution, painting black-top walkways white) were implemented in only 25% of events but showed operational value
- Active clinical cooling protocols (ice-water immersion, forced-air cooling) were critical for heatstroke management but explicitly detailed in only 19% of studies
- Real-time WBGT monitoring and syndromic surveillance enabled rapid resource deployment; automated threshold alerts triggered proactive cooling and hydration in Caribbean Cricket World Cup (2024)
- No studies demonstrated formal pre-event vulnerability screening systems despite older adults and those with chronic disease bearing overwhelming HRI burden
- Digital risk communication (SMS, mobile apps, multilingual messaging) showed high user acceptability (84% favoured SMS at Super Bowl) but did not reliably translate into protective behaviours
Summary of clinical encounters, heat-related illness and medical triage outcomes across mass gathering typologies
Table extracted from the guideline
| Event category | Studies | Total clinical encounters | Total HRI (%) | Heatstroke (classical/exertional) | Heat exhaustion/syncope/dehydration | Successfully managed on-site (%) | Transferred to hospital (%) | Total deaths |
|---|---|---|---|---|---|---|---|---|
| Music and concerts | 46, 48, 49, 58, 60–62 | 18,826 | 498 (2.6%) | 21 | 171 | 17,003 (90.3%) | 1,399 (7.4%) | 0 |
| Religious | 43, 44, 52–57, 59, 63 | 415,643 | 19,042 (4.6%) | 2,650 | 15,918 | 393,248 (94.6%) | 1,515 (0.4%) | 1,194 |
| Sporting | 47, 50, 51, 58, 64–73 | 21,411 | 2,635 (12.3%) | 0 | 2,635 | 8,634 (40.3%) | 364 (1.7%) | 0 |
| Other | 74–77 | 28,026 | 22 (<0.1%) | 0 | 9 | 24,220 (86.4%) | 1,263 (4.5%) | 2 |
| Total | All | 483,906 | 22,197 (4.6%) | 2,671 | 18,733 | 443,105 (91.6%) | 4,541 (0.9%) | 1,196 |
Source: World Health Organization, Prevention and management of heat-related illness at mass gatherings: systematic reviews. Reproduced in summary form.
From the guideline
Verbatim
“More than 90% were managed and discharged on-site, indicating that well-organized event medical systems can substantially reduce pressure on hospitals and ambulance services.”
Editor’s perspective
Why this matters for Georgia and the region
Prof. Giorgi Pkhakadze, MD, MPH, PhD
Editor-in-Chief, Georgian Medical Journal · Chair, Public Health Institute of Georgia · WHO consultant, health and migration
As Georgia increasingly hosts international sporting events and religious gatherings, and as our region experiences rising summer temperatures, this WHO evidence synthesis arrives at a critical moment. I would stress to Georgian clinicians and event planners the finding that 92% of nearly half a million patient encounters were successfully managed on-site when proper medical infrastructure was deployed—this demonstrates that investment in tiered field hospitals with emergency physicians and ice-water immersion capability is not merely advisable but cost-effective, preventing overwhelming of our municipal emergency departments. The most concerning gap for our context is the complete absence of pre-event vulnerability screening systems in the global literature, despite older adults with cardiovascular disease and diabetes bearing the overwhelming HRI burden—conditions highly prevalent in Georgia. One realistic implementation challenge we must acknowledge: the documented knowledge–action gap means that even excellent risk communication may not change behaviour, particularly where cultural or religious imperatives are strong; our national programmes will need to move beyond information provision toward structural interventions that make protective behaviours the default, not the choice.
ORCID 0000-0001-7609-4515 · Perspective written for the GMJ Guidelines Library, 17 Oct 2026
Applicability
Georgia and the South Caucasus
Georgia and the South Caucasus region host significant mass gatherings including religious pilgrimages, sporting events and outdoor festivals, with climate projections indicating increasing frequency and intensity of extreme heat events across the region. The Georgian Public Health Institute and Ministry of Health should prioritize developing standardized mass-gathering medical capacity including tiered on-site clinical infrastructure, active cooling protocols (ice-water immersion capability for heatstroke), and environmental modifications tailored to local event types. Critical gaps to address include: establishing formal pre-event vulnerability screening for older adults and those with cardiovascular disease and diabetes (conditions with high prevalence in Georgia), implementing real-time WBGT monitoring and syndromic surveillance linked to operational response protocols, and developing culturally appropriate multilingual risk communication for diverse attendees at international events. National programmes should integrate these evidence-based interventions into existing emergency preparedness frameworks and universal health coverage systems, ensuring equitable access to cooling infrastructure and medical services across all population groups.
Questions this guideline answers
Quick answers
What are the most effective interventions to reduce heat-related illness at mass gatherings?
Robust on-site medical infrastructure with emergency physicians is the most consistently effective intervention, enabling 92% of patients to be managed without hospital transfer. This should be combined with active cooling protocols (ice-water immersion for heatstroke), environmental modifications (cooling shelters, misting systems, free water), real-time WBGT monitoring, and culturally tailored multilingual risk communication. These function as complementary layers rather than standalone interventions.
Which populations are at highest risk for severe heat-related illness at mass gatherings?
Older adults (especially those over 50 years) with pre-existing comorbidities face highest risk. Religious mass gatherings documented populations with hypertension (up to 61.6%), diabetes (up to 47.7%) and cardiovascular disease (up to 14.4%) experiencing severe heatstroke and mortality. Age-related declines in thermoregulation, altered thirst perception and chronic disease effects create profound physiological disadvantage under heat stress.
How can event organizers identify vulnerable attendees before heat exposure occurs?
The evidence base shows a critical gap: no studies demonstrated formal pre-event vulnerability screening systems. Current practice identifies vulnerability only retrospectively after clinical presentation. Future approaches should develop pre-registration health screening, special ticketing categories for high-risk groups, and proactive mechanisms linked to targeted cooling access and medical monitoring, though these remain to be validated in practice.
Do digital health technologies and wearable sensors effectively prevent heat-related illness?
Real-time syndromic surveillance systems linked to operational response showed effectiveness (e.g., automated threshold alerts triggering rapid cooling deployment at 2024 Cricket World Cup). However, most AI-enabled wearables and predictive models remain in pilot stages with small, unrepresentative cohorts. Static meteorological prediction models alone had limited real-world value. Effective systems require integration of environmental, physiological and clinical data with defined response protocols, not technology in isolation.
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Other guidelines on this topic
- Prevention and management of heat-related illness at mass gatherings: considerations for implementation
- Prevention and management of heat-related illness at mass gatherings: developing evidence-based communication messages
- Prevention and management of heat-related illness at mass gatherings: risk assessment tool
- Resilient Hospitals: An inter-regional guidance on strengthening resilience to health emergencies and disasters in health facilities
- EVAC-H: Evacuation of hospitals and their critical areas
- Issuer
- World Health Organization
- Type
- Manual
- Edition
- 2026
- Status
- Current
- Published
- 2026-09-30
- Languages
- English
- Scope
- Global systematic reviews covering mass gatherings 1978–2024 with >70 million cumulative attendance
- Audience
- Governments and organizations hosting mass gatherings; decision-makers at international, national, regional and municipal levels; public health professionals; event medical planners; community health workers
- Pages
- 118
- Licence
- CC BY-NC-SA 3.0 IGO
- Evidence
- Systematic reviews with ROBINS-I and PROBAST risk-of-bias assessment; narrative synthesis following SWiM guidelines; 54 studies included across three reviews
- Record history
- Created 17 Oct 2026 · updated 17 Oct 2026 · next check Apr 2027
Prevention and management of heat-related illness at mass gatherings: systematic reviews. Geneva: World Health Organization; 2026. https://doi.org/10.2471/B09849. Licence: CC BY-NC-SA 3.0 IGO.GMJ Guidelines Library records are original summaries written by the GMJ editorial team from the issuer’s published document and reviewed by a physician. They do not replace the full guideline. The document is the copyright of its issuer and is linked, not hosted. Spotted an error or a newer edition? Tell the Guidelines Desk.
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