The Al-Bahah Paradox: Divergent Patterns of Increased and Decreased Infectious Disease Incidence Relative to National...

To 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.

In 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.

Overall 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).

Al-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.