Weather, season, and daily stroke admissions in Hong Kong

Abstract

Previous studies examining daily temperature and stroke incidence have given conflicting results. We undertook this retrospective study of all stroke admissions in those aged 35 years old and above to Hong Kong public hospitals from 1999 through 2006 in order to better understand the effects of meteorological conditions on stroke risk in a subtropical setting. We used Poisson Generalized Additive Models with daily hemorrhagic (HS) and ischemic stroke (IS) counts separately as outcomes, and daily mean temperature, humidity, solar radiation, rainfall, air pressure, pollutants, flu consultation rates, day of week, holidays, time trend and seasonality as predictors. Lagged effects of temperature, humidity and pollutants were also considered. A total of 23,457 HS and 107,505 IS admissions were analyzed. Mean daily temperature had a strong, consistent, negative linear association with HS admissions over the range (8.2-31.8°C) observed. A 1°C lower average temperature over the same day and previous 4 days (lags 0-4) being associated with a 2.7% (95% CI: 2.0-3.4%, P < .0.0001) higher admission rate after controlling for other variables. This association was stronger among older subjects and females. Higher lag 0-4 average change in air pressure from previous day was modestly associated with higher HS risk. The association between IS and temperature was weaker and apparent only below 22°C, with a 1°C lower average temperature (lags 0-13) below this threshold being associated with a 1.6% (95% CI:1.0-2.2%, P < 0.0001) higher IS admission rate. Pollutant levels were not associated with HS or IS. Future studies should examine HS and IS risk separately.

Both low and high temperature may increase the risk of stroke mortality

“…40 In our analysis, similar effects of temperature were observed before and after Table 2 Pooled relative risks and their 95% posterior intervals of cold and hot temperatures on stroke mortality over multiple lag days in 8 adjusting for PM 10 , SO 2 , and NO 2 (data not shown), suggesting that our findings were robust against this potential confounder. We were unable to adjust for fine particles and ozone because they were not criteria pollutants in China and were not routinely monitored during the study period.…”

“…Similar findings on low temperature and higher stroke occurrence were also reported in South Korea, 23 northern Portugal, 24 and Hong Kong. 8 On the other hand, hot temperature was linked to higher stroke risk in studies in Scotland, 25 Mantua (Italy), 9 New York City, 26 California, 27 Brisbane (Australia), 28 and 4 cities in Korea. 29 In the present study, we found that the associations between temperature and stroke mortality were often nonlinear-both low and high temperatures were linked to more stroke deaths.…”

“…Previous studies have reported different impacts of ambient temperature on ischemic and hemorrhagic stroke. 8,29 Finally, this study was inherently an ecologic analysis and thus potential confounding from individual-level risk factors could not be fully excluded.…”

“…Seasonal variations of stroke incidence and mortality have been widely reported worldwide, although the peak season was often different across countries, such as spring in Japan, 6 summer in Turkey, 7 and winter in Hong Kong. 8 However, the existing epidemiologic findings on ambient temperature and stroke are inconsistent. 9 We therefore examined the effects of temperature on daily stroke mortality in 8 Chinese cities using a standardized analytic protocol.…”

Humidity: A review and primer on atmospheric moisture and human health

“…More often, humidity is treated as a confounding variable that may be related to both the predictor and response variables (Barnett et al, 2010;Zhang et al, 2014). This approach is a part of the analysis strategy in numerous studies (Cao et al, 2009;Goggins et al, 2012;Guo et al, 2012;Lim et al, 2013;Liu et al, 2011;Vaneckova and Bambrick, 2013;Wang et al, 2009), although this list is certainly not exhaustive. Alternate approaches incorporate humidity in biometeorological indices (such as AT or Hx) or include it as an input variable in human heat 20 balance models.…”