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Effect modification of consecutive high concentration days on the association between fine particulate matter and mortality: a multi-city study in Korea
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Hyungryul Lim
 , Sanghyuk Bae, Jonghyuk Choi, Kyung-Hwa Choi, Hyun-Joo Bae, Soontae Kim, Mina Ha, Ho-Jang Kwon
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Epidemiol Health. 2022;44:e2022052. Published online June 9, 2022
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DOI: https://doi.org/10.4178/epih.e2022052
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 Abstract
Summary
 PDF Supplementary Material
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Abstract
OBJECTIVES
Although there is substantial evidence for the short-term effect of fine particulate matter (PM2.5) on daily mortality, few epidemiological studies have explored the effect of prolonged continuous exposure to high concentrations of PM2.5. This study investigated how the magnitude of the mortality effect of PM2.5 exposure is modified by persistent exposure to high PM2.5 concentrations.
METHODS We analyzed data on the daily mortality count, simulated daily PM2.5 level, mean daily temperature, and relative humidity level from 7 metropolitan cities from 2006 to 2019. Generalized additive models (GAMs) with quasi-Poisson distribution and random-effects meta-analyses were used to pool city-specific effects. To investigate the effect modification of continuous exposure to prolonged high concentrations, we applied categorical consecutive-day variables to the GAMs as effect modification terms for PM2.5.
RESULTS The mortality risk increased by 0.33% (95% confidence interval [CI], 0.16 to 0.50), 0.47% (95% CI, -0.09 to 1.04), and 0.26% (95% CI, -0.08 to 0.60) for all-cause, respiratory, and cardiovascular diseases, respectively, with a 10 μg/m3 increase in PM2.5 concentration. The risk of all-cause mortality per 10 μg/m3 increase in PM2.5 on the first and fourth consecutive days significantly increased by 0.63% (95% CI, 0.20 to 1.06) and 0.36% (95% CI, 0.01 to 0.70), respectively.
CONCLUSIONS We found increased risks of all-cause, respiratory, and cardiovascular mortality related to daily PM2.5 exposure on the day when exposure to high PM2.5 concentrations began and when exposure persisted for more than 4 days with concentrations of ≥35 μg/m3. Persistently high PM2.5 exposure had a stronger effect on seniors.
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Summary
Korean summary
한국의 7개 대도시를 배경으로 수행한 본 시계열 연구를 통하여 2006년부터 2019년까지의 기간 동안에 초미세먼지의 단기 노출이 일별 사망률을 증가시키며, 교호작용모형을 통해 일평균 35 μg/m3 이상의 고농도 지속기간이 처음 시작되는 날과 넷째 지속일에 이러한 사망효과가 커짐을 보고하였다. 이러한 고농도 지속기간의 교호작용은 65세 이상 연령군에서 더욱 두드러졌다.
Key Message
With our Korean multi-city study design from 2006 to 2019, the short-term effects of PM2.5 on mortality were greater when the high PM2.5 concentration duration began during the day and lasted for approximately 4 days, and the elderly may be more affected by persistently high PM2.5.
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