The association between cold spells and admissions of ischemic stroke in Hefei, China: Modified by gender and age

Some studies have discovered that low ambient temperatures were associated with increased risk of the incidence of ischemic stroke. Although the frequency of extreme weather events is increasing, few studies have studied the effects of cold wave on ischemic stroke. The purpose of this study was to explore the association between cold waves and ischemic stroke onset and further to explore how this association was modified by cold spell characteristics and individual-level factors. A Poisson regression with a distributed lag nonlinear model was used to investigate the association between cold spells under 9 different definitions and daily admissions of ischemic stroke in 2013–2015 in Hefei. By comparing the attribution risk and the results of the sensitivity analysis of different models, the local optimal cold spell was defined as the day between November to March when daily mean temperature was less than 10th for 2 or more consecutive days (backward attributable risk fraction (b-AF) = 4.19%, 95% empirical confidence intervals (eCI): 0.87%, 6.66%, backward attributable number (b-AN) = 278). On the basis of optimal model, the single-day effect of cold waves on ischemic stroke occurred on 5th day after exposure and continued until 17th day, and the maximum effect appeared on the 5th day with relative risk (RR) = 1.050 (95% confidence interval (CI) = 1.008, 1.094). The significant cumulative effect lasted from day 9 after exposure to cold spells to day 21. The maximum cumulative effect was observed on the 21st day with RR = 2.378 (95% CI = 1.304, 4.337). The female and the young and middle-aged people were susceptible to the local cold waves. This study suggests that cold spell is a risk factor for ischemic stroke in Hefei, and there is a certain lag effect. Targeted measures should be taken to protect susceptible populations during cold spell days, including women and young and middle-aged people.