Health impacts of the Southeast Asian haze problem – A time-stratified case crossover study of the relationship between ambient air pollution and sudden cardiac deaths in Singapore

To investigate the association between air pollution and out-of-hospital cardiac arrest (OHCA) incidence in Singapore. A time-stratified case-crossover design study. OHCA incidences of all etiology in Singapore. 8589 OHCA incidences reported to Pan-Asian Resuscitation Outcomes Study (PAROS) registry in Singapore between 2010 and 2015. A conditional Poisson regression model was applied to daily OHCA incidence that included potential confounders such as daily temperature, rainfall, wind speed, Pollutant Standards Index (PSI) and age. All models were adjusted for over-dispersion, autocorrelation and population at risk. We assessed the relationship with OHCA incidence and PSI in the entire cohort and in predetermined subgroups of demographic and clinical characteristics. 334 out of 8589 (3.89%) cases survived. Moderate (Risk ratio/RR = 1.1, 95% CI = 1.07–1.15) and unhealthy (RR =1.37, 95% CI = 1.2–1.56) levels of PSI showed significant association with increased OHCA occurrence. Sub-group analysis based on individual demographic and clinical features showed generally significant association between OHCA incidence and moderate/unhealthy PSI, except in age 65, male, Indian and non-traumatic. Each increment of 30 unit in PSI on the same day and previous 1–5 days was significantly associated with 5.8–8.1% increased risk of OHCA (p