Spatial analysis of cardiovascular disease morbidity among residents of Ulaanbaatar

Abstract

Background: Cardiovascular disease (CVD) remains the leading cause of death in Mongolia. Khoroos of Ulaanbaatar differ markedly in settlement type, green space and air pollution, but standardised CVD morbidity has not been mapped at this level. Aim: To standardise registered CVD and hypertension morbidity across khoroos of the six central districts, identify hot and cold spots, and describe their environmental characteristics. Materials and Methods: This registry-based ecological cross-sectional study used 2022 and 2024 individual-level records of CVD (I00–I99, excluding venous diseases) and hypertension (I10–I15) for residents of 189 khoroos. Repeat visits were removed so that each person was counted once per year, and the 33 khoroos created in 2022 were merged with their parent khoroos (156 units). Rates were standardised directly to the WHO world population and indirectly by age and sex (standardised morbidity ratio, SMR). Hot and cold spots were identified with the Getis-Ord Gi* statistic and compared with environmental indicators using Spearman correlation. The study was approved by the Research Ethics Committee of the Mongolian National University of Medical Sciences (No. 2022/3-11). Results: In total, 192,665 person-years with CVD and 86,902 with hypertension were registered. The city-wide agestandardised rate per 10,000 population was 747.2 for CVD and 341.2 for hypertension. CVD rates varied 2.1-fold between districts (Khan-Uul 477.2, Bayangol 979.1). CVD (Moran’s I=0.19) and hypertension (I=0.12) showed weak but significant clustering. Of the 16 CVD hot spots, 15 were in Bayangol district, and 14 of the 16 cold spots were in KhanUul district. Hot spots were dense central khoroos with little green space (median 2.3%) and higher PM2.5 (44.6 µg/m3); cold spots had abundant green space (70.4%) and lower PM2.5 (26.3 µg/m3). SMRs correlated inversely with green space (ρ=−0.36) and positively with PM2.5 and SO2 (ρ=0.25–0.29), but not with the share of ger areas or elevation. Only 4.4% of CVD records of Khan-Uul residents came from the district health centre (27.6–47.3% elsewhere). Conclusion: In Ulaanbaatar, registered CVD and hypertension morbidity is higher in densely built central khoroos with little green space and lower in the green southern khoroos. Hot and cold spots follow district boundaries, suggesting that part of the observed variation reflects differences in access to care and in registration practice.