• Andrew F W Ho, Huili Zheng, Deidre A De Silva, Win Wah, Arul Earnest, Yee H Pang, Zhenjia Xie, Pin P Pek, Nan Liu, Yih Y Ng, Ting H Wong, Ling L Foo, and Ong Marcus E H MEH Health Services and Systems Research, Duke-NUS Medical School, Singapore; Department of Emergency Medicine, Singapore General Hospital, Singapore..
• SingHealth Emergency Medicine Residency Programme, Singapore Health Services, Singapore; Emergency Medicine Academic Clinical Programme, Singhealth Duke-NUS, Singapore; Cardiovascular and Metabolic Disorders Program, Duke-NUS Medical School, Singapore. Electronic address: sophronesis@gmail.com.
• Ann Emerg Med. 2018 Nov 1; 72 (5): 591-601.

Study ObjectiveStudies are divided on the short-term association of air pollution with stroke. Singapore is exposed to seasonal transboundary haze. We aim to investigate the association between air pollution and stroke incidence in Singapore.MethodsWe performed a time-stratified case-crossover analysis on all ischemic stroke cases reported to the Singapore Stroke Registry from 2010 to 2015. Exposure on days was compared with control days on which exposure did not occur. Control days were chosen on the same day of the week earlier and later in the same month in the same year. We fitted a conditional Poisson regression model to daily stroke incidence that included Pollutant Standards Index and environmental confounders. The index was categorized according to established classification (0 to 50=good, 51 to 100=moderate, and ≥101=unhealthy). We assessed the relationship between stroke incidence and Pollutant Standards Index in the entire cohort and in predetermined subgroups of individual-level characteristics.ResultsThere were 29,384 ischemic stroke cases. Moderate and unhealthy Pollutant Standards Index levels showed association with stroke occurrence, with incidence risk ratio 1.10 (95% confidence interval 1.06 to 1.13) and 1.14 (95% confidence interval 1.03 to 1.25), respectively. Subgroup analyses showed generally significant association, except in Indians and nonhypertensive patients. The association was significant in subgroups aged 65 years or older, women, Chinese, nonsmokers and those with history of diabetes, hypertension, and hyperlipidemia. Stratified by age and smoking, the risk diminished in smokers of all ages. Risk remained elevated for 5 days after exposure.ConclusionWe found a short-term elevated risk of ischemic stroke after exposure to air pollution. These findings have public health implications for stroke prevention and emergency health services delivery.Copyright © 2018 American College of Emergency Physicians. Published by Elsevier Inc. All rights reserved.

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