Acute effects of ambient ozone on daily hospital admissions and daily mortality for respiratory and cardiovascular diseases among residents of Bangkok, Thailand

Abstract

The purpose of this study was to investigate the acute effects of ambient ozone (O₃) exposure on health outcomes among residents of Bangkok, Thailand. The health outcomes were defined as daily hospital admissions for pneumonia, asthma, myocardial infarction (MI), and chronic obstructive pulmonary disease (COPD) between September 2002 to September 2004, and mortality from respiratory and cardiovascular diseases and unclassified causes between January 2001 and December 2004. A negative binomial regression model was used to conduct a time-series analysis of the counts. The effects of time trend, seasonality, day of the week, temperature, and relative humidity were adjusted and overdispersion was corrected. Daily 1-hour maximum concentrations of O₃ were averaged from eleven monitoring stations throughout Bangkok. Relative risks (RR _S) of health outcomes (per 10 ppb increase in air pollutant concentration) were calculated.

A 10-ppb increase in daily 1-hour maximum O₃ was statistically significantly associated with estimated increases in daily all-cause mortality of 0.5-0.7% for all-age group (lag of 0-, 1-, 2- and 3-day) and 0.6-0.7% for the 55-79 age group (lag of 0- and 3-day). Daily O₃ concentrations were positively associated with daily mortality from cardiovascular diseases among both all-age group and the 55-79 age group, but this association was not significant. There was only a marginally significant association between daily O₃ concentration (lag of 2-day) and daily mortality from respiratory diseases in the 55-79 age group (2.1% increase per 10-ppb increment, 95% CI = 1.000, 1.043). The effects were the strongest for unclassified-cause mortality (1.3% increase per 10-ppb increment, 95% CI = 1.006, 1.021 for all-age group and 2.0% increase per 10 ppb increment, 95% CI = 1.008, 1.033 for the 55-79 age group) at current exposure (lag of 0-day).

Daily O₃ concentration (lag of 3-day) was statistically significantly associated with daily pneumonia admissions in the 55-79 age group (5% increase in pneumonia admissions per 10-ppb increment, 95% CI = 1.008, 1.095). Daily O₃ concentration (lag of 1-day) was statistically significantly associated with daily asthma admissions in the all-age group (3% increase in daily counts of asthma admissions per 10-ppb increment, 95% CI = 1.001, 1.061). The strongest effect was observed at current exposure (lag of 0-day) in children of 5-14 years (7.1% increase in daily counts of asthma admissions per 10-ppb increment, 95% CI = 1.001, 1.147). No statistically significant associations were found between daily O₃ concentrations and hospital admissions for COPD and MI at any lagged exposure. The cumulative effects of O₃ exposure produced asthma readmissions in < 5 age group. During a 21-day period, the readmissions for < 5 age group took place when average daily exposure was greater than 41.13 ppb. The cumulative effects of O₃ exposure on asthma readmissions were mixed in all-age, 5-14, 25-44, 45-64, and 65+ age groups.