Effects of smoke haze on respiratory clinic visits in Central Kalimantan, Indonesia according to different haze characteristics.

BACKGROUND: Smoke haze is a common air-pollution issue in Southeast Asia. Studies have suggested an elevated respiratory risk due to smoke-haze exposure. However, relevant studies have applied different exposure assessments in addressing haze effects and there is no unified definition of haze due to differences in its characteristics by location. The present study aimed to examine the effects of haze on respiratory health outcomes by analysing local fire activity and duration. METHODS: Data for daily respiratory visits in Central Kalimantan were collected at local primary healthcare centers ('puskesmas') during the period spanning 2015-2019, encompassing two major haze episodes in the region. Particulate matter with aerodynamic diameter <10 μm and fire hotspot counts were used to determine haze days, including fire-haze and non-fire-haze days. A space-time-stratified case-crossover design was used through a conditional quasi-Poisson regression model to examine the effects of haze vs. non-haze days in each subdivision, with lags of up to five  days, for different haze definitions and durations. RESULTS: The risk of respiratory visits was prominent during haze days but varied by haze characteristics. There was a 36.6% (95% confidence interval: 10.2%, 69.3%) and 74.4% (18.9%, 164.6%) increased risk of respiratory visits in Pulang Pisau Regency during haze and fire haze, respectively. The risk was pronounced when the haze was characterized by longer durations. CONCLUSION: Our findings suggest inconclusive effects of haze on respiratory visits to primary healthcare centers, although they appeared to be prominent in the area mainly dominated by fire haze. Haze characteristics should be analysed carefully for differences in risk patterns according to location.