Patterns of illness among 551,983 patients during the 2025 Arbaeenia mass gathering in Iraq

The Arbaeenia mass gathering in Iraq is one of the largest annual religious events globally, drawing millions of pilgrims and placing substantial pressure on health systems along major pilgrimage routes. Understanding the clinical characteristics of patients seeking care during this period is essential for strengthening preparedness and optimizing resource allocation. This study provides a large-scale assessment of mobile health-facilities presentations during the Arbaeenia mass gathering. We conducted a secondary analysis of collected data from 634 mobile medical clinics operating along major pilgrimage routes and in Karbala and surrounding governorates during the Arbaeenia event (23 July–16 August 2025). Standardized forms captured demographics, chronic diseases, clinical presentations, fever syndromes, and injury types, following national mass-gathering surveillance protocols. The dataset included all documented encounters, totaling 551,983 records, based on syndromic assessments and clinician-reported symptoms. A total of 551,983 patients attended mobile clinics. Most were male (56.1%) and aged 16–35 years (49.5%). Iraqi nationals comprised 73.6% of attendees, followed by Iranian pilgrims (23.7%). Chronic diseases were reported in 5.8% of patients, mainly among adults >45 years, with hypertension and diabetes predominating. Presentations were dominated by non-specific pain syndromes, including headache (32.7%), joint pain (25.1%), and muscle pain (14.4%), followed by skin rash (12.2%), fatigue (9.7%), and gastrointestinal or respiratory symptoms. Fever occurred in 3.5% of visits; most cases (86.5%) involved uncomplicated fever. Injuries accounted for 3.6% of consultations, primarily superficial wounds and minor musculoskeletal trauma. Healthcare utilization in mobile medical clinics during the Arbaeenia mass gathering was driven largely by high-volume, low-acuity complaints. Findings highlight the need to strengthen healthcare capacity, ensure medication continuity for chronic diseases, enhance syndromic surveillance, and tailor services for vulnerable age groups to support effective mass-gathering health responses.