The Al-Bahah Paradox: Divergent Patterns of Increased and Decreased Infectious Disease Incidence Relative to National Saudi Rates Over 12 Years of Surveillance.

ObjectiveTo identify statistically significant deviations in notifiable infectious disease incidence between Al-Bahah region and national Saudi averages, and to generate hypotheses that may inform future epidemiological, microbiological, and public health investigations.MethodsIn April 2026, a 12-year retrospective ecological study (2013-2024) was conducted using surveillance data from the Saudi Ministry of Health for 37 notifiable infectious diseases across 20 health regions. Cumulative incidence rates, standardized morbidity ratios (SMRs), and Z-tests compared observed cases in Al-Bahah against national estimates.ResultsOverall incidence was 15.8% lower in Al-Bahah than nationally (86.42 versus 102.68; incidence rate ratios = 0.842; p = 1.6×10-31), but this aggregate reduction concealed a bidirectional divergence. Reduction anomalies: dengue fever absent; amoebic dysentery reduced by 95%; measles by 76%; malaria by 60%. Excess anomalies: schistosomiasis increased 713%; pneumococcal meningitis 600%; Salmonella food poisoning 232%; brucellosis 73%. A 2021 Salmonella outbreak reached 155.95/100,000 (>20-fold national peak).ConclusionAl-Bahah exhibited lower incidence of diseases including vector-borne and fecal-oral diseases but higher incidence of several other diseases like zoonotic, foodborne, and freshwater-associated infections relative to national rates. These ecological observations generate hypotheses regarding regional differences in disease transmission, diagnosis, surveillance, and healthcare utilization that warrant further investigation using individual-level data. If confirmed, such findings may have implications for region-specific public health planning, laboratory preparedness, and clinical decision-making.