Carbon monoxide and stroke: A time series study of ambient air pollution and emergency hospitalizations.
BACKGROUND
Recent experimental and clinical studies suggested that exogenous carbon monoxide (CO) at low concentrations may have beneficial neuroprotective effects under certain circumstances. However, population-based epidemiological studies of environmentally relevant CO exposure generated mixed findings. The present study aimed to examine the short-term association of ambient CO with emergency stroke hospitalizations.


METHODS
A time series study was conducted. Daily air pollution concentrations and emergency hospital admission data from January 2004 to December 2011 in Hong Kong were collected. Generalized additive Poisson models were used to estimate the associations between daily 24-hour mean concentrations of CO and emergency hospital admissions for stroke, while controlling for other traffic related co-pollutants: NO₂ and PM₂.₅. Sensitivity analyses were performed using daily 1-hour maximum concentration of CO as exposure indicator.


RESULTS
Negative associations were observed between ambient CO concentrations and emergency hospital admissions for stroke. The previous 1-3 day cumulative exposure to CO was associated with a -2.0% (95%CI, -3.3% to -0.7%) decrease in stroke admissions per interquartile range (IQR) increment in CO concentration (0.3 ppm). Similar results were obtained when using 1-hour maximum concentration of CO as exposure indicator. The negative association was robust to the co-pollutant adjustment for either NO₂ or PM₂.₅. Females and elders appeared to be more sensitive to ambient CO exposure. The negative association tended to be larger in cool season.


CONCLUSIONS
Short-term exposure to ambient CO was associated with decreased risk of emergency hospitalizations for stroke, suggesting some acute protective effects of CO exposure against stroke onsets.
School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China. Electronic address: linweit@hku.hk.
Linwei
L
Tian
School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China.
Hong
H
Qiu
The Jockey Club School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong Special Administrative Region, China.
Vivian C
VC
Pun
The Jockey Club School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong Special Administrative Region, China.
Kin-Fai
KF
Ho
The Jockey Club School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong Special Administrative Region, China.
Chi Sing
CS
Chan
The Jockey Club School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong Special Administrative Region, China.
Ignatius T S
IT
Yu
D000368:Aged; D000369:Aged, 80 and over; D000397:Air Pollution / Q000009:adverse effects*; D002248:Carbon Monoxide / Q000009:adverse effects*; D004305:Dose-Response Relationship, Drug; D004632:Emergency Medical Services / Q000639:trends*; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006760:Hospitalization / Q000639:trends*; D006801:Humans; D065186:Interrupted Time Series Analysis / Q000639:trends; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D052638:Particulate Matter / Q000009:adverse effects*; D020521:Stroke / Q000175:diagnosis / Q000453:epidemiology*
D052638:Particulate Matter; D002248:Carbon Monoxide
Carbon monoxide; Emergency hospital admission; Stroke; Time series study