International Journal of Hygiene and Environmental Health
Cardiorespiratory hospitalizations associated with smoke exposure during the 1997 Southeast Asian forest fires
Introduction
In 1997, uncontrolled forest fires burned in the Indonesian states of Kalimantan and Sumatra. The fires, in combination with a severe drought, produced a regional air pollution episode that affected Malaysia, Singapore, Thailand, Brunei and the Philippines. During a continuous two-month period, an estimated 20 million people were exposed to ambient concentrations of particulate matter (PM10) that exceeded the US EPA's 24 h National Ambient Air Quality Standard of 150 μg/m3 (Brauer et al., 2001). On September 22, 1997, 24-h PM10 concentrations peaked at 852 μg/m3 in Kuching, the capital of the state of Sarawak, Malaysia. This peak concentration exceeded the US EPA's 24-h hazardous level of 500 μg/m3.
As population expansion into wildland environments continues, human exposures to forest fire smoke are likely to increase (US Centers for Disease Control and Prevention, 1999, US Centers for Disease Control and Prevention, 2001, US Centers for Disease Control and Prevention, 2002; Ward, 1999). A limited number of epidemiologic investigations suggest that population exposures to wood smoke are associated with increased self-reporting of respiratory symptoms (US Centers for Disease Control and Prevention, 2002; Larson and Koenig, 1994; Shusterman et al., 1993) and increased emergency department admissions for chronic obstructive pulmonary disease (COPD), bronchitis, asthma, and chest pain (US Centers for Disease Control and Prevention, 1999, US Centers for Disease Control and Prevention, 2001; Mott et al., 2002; Duclos et al., 1990). However, these health endpoints are influenced by individual perceptions and decisions to seek medical care. Thus they are somewhat subjective and can increase with the psychosomatic stress that is often associated with air pollution emergencies. Population densities of exposed communities have not commonly been large enough to produce sample sizes sufficient to assess epidemiologic relationships between poor air quality and more objective and severe indicators of morbidity such as hospitalizations for cardiorespiratory problems (US Centers for Disease Control and Prevention, 2001).
When dispensing intervention resources into smoke-exposed communities, public health professionals tend to assume that older persons, and persons with COPD, are most susceptible to the adverse health effects of forest fire smoke exposure (Mott et al., 2002). However, an assessment of cardiorespiratory health effects in cohorts of exposed and unexposed persons of different ages and disease histories has not been undertaken. The systematic identification of those most susceptible to forest fire smoke exposures remains necessary for the development of science-based recommendations for public outreach and targeted intervention.
In this study we investigate the cardiorespiratory health effects of the 1997 Southeast Asian forest fires among persons who were hospitalized at any of seven hospitals in the region of Kuching, Malaysia between January 1, 1995 and December 31, 1998. Specifically, this study has three objectives:
- 1.
To determine whether there was an increase in total hospitalizations, cardiovascular hospitalizations, and respiratory hospitalizations during the months of the forest fires in 1997 relative to the non-fire years of 1995 and 1996, adjusting for seasonal variation in admissions.
- 2.
To assess whether cohorts of persons with previous hospital admissions for cardiorespiratory diseases were more likely to be readmitted for the same condition during the forest fires of 1997 than during the same months during pre-fire years of 1995 and 1996.
- 3.
To assess the duration of any longer term post-fire health effects (in the form of longer term increases in re-hospitalization rates among persons with a history of disease) in cohorts of persons exposed to the forest fire smoke.
Hospitalization data provided by the Sarawak Health Department provided a unique opportunity to undertake this investigation as: (a) the population density of exposed persons was sufficient to permit cohort analyses of hospitalizations, and (b) the absence of significant industrial pollution permitted an independent assessment of the health effects of forest fire smoke exposure (Sastry, 2002).
Section snippets
Data source
Hospitalizations were selected from a database of all public hospital admissions that occurred in the state of Sarawak, Malaysia between January 1, 1995 and December 31, 1998. Analyses were limited to hospitalizations that occurred in the Kuching region, the area of Sarawak where air quality was most continuously monitored during the 1997 forest fires. The hospitals included in these analyses were Sarawak General Hospital, Lundu District Hospital, Bau District Hospital, Serian District
Descriptive analyses
There were 190,016 hospitalizations for any cause in the region of Kuching, Malaysia during the period of 1995 to 1998. Of these hospitalizations, 20,488 (10.8%) were for respiratory problems, 13,103 (6.9%) were for circulatory problems, 9816 (5.2%) were for COPD and 5558 (2.9%) were for asthma. The total number of hospitalizations was also evenly distributed across years (46,061 hospitalizations in 1995; 49,796 in 1996; 48,721 in 1997; and 45,258 in 1998) (Table 1).
Over 40% (80,605) of the
Discussion
These findings demonstrate that many communities exposed to forest fire smoke during the Southeast Asian forest fires of 1997 experienced short-term increases in cardiorespiratory hospitalizations. Significant increases in respiratory hospitalizations, particularly those due to asthma, were observed in the 19–39 and 40–64 age categories. Survival analyses indicated that persons over age 65 with prior hospitalizations for respiratory diseases were significantly more likely than others to be
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