Piloting surveillance of environmental risks and cardiovascular events in Delhi and Shimla, India, 2021

Air pollution and extreme heat are significant environmental risk factors contributing to cardiovascular disease (CVD) morbidity and mortality in changing climate. The National Outdoor Air and Disease Surveillance (NOADS) collects daily aggregates of respiratory-specific emergencies and interventions from selected tertiary hospitals in highly polluted cities since 2017. We piloted hospital-based surveillance to capture environmental risk factors’ impact on CVD events and provide evidence-based recommendations for their inclusion in NOADS. Daily CVD events (emergency admissions and deaths) were collected from selected tertiary care facilities of Delhi and Shimla, with meteorological data, between January and July 2021. We used generalized additive modelling with temporal lags, adjusting for temperature and humidity. Distribution of individual CVD risk factors and diagnosis was assessed. We analysed 41,436 eligible admissions, including 11,494 CVD events in Delhi and 3,849 in Shimla. In Delhi, CVD events increased by 1.8% (95% CI:0.5%-3.05), 1.2% (95% CI:0.1%-2.3%) and 2.0% (95% CI:0.7%-3.2%) per 10-unit increase in AQI, PM10, and PM2.5, respectively at one-day lag. Shimla showed inconsistent, non-significant associations. There were significant differences in some individual risk factors, e.g., lower mean age, exercise and high dietary risk in Delhi, and higher smoking and solid fuel for cooking in Shimla. Ischemic heart disease was major CVD outcome. Our results support integrating CVD outcome and environmental risk factor tracking into NOADS. It can expand its capacity to track a broader range of health effects, thereby supporting evidence-based health sector preparedness, localized planning, and targeted air quality management interventions in India’s diverse urban environments.