Researchers examined nearly 75,000 emergency department visits for asthma and COPD between February 2016 and December 2022. The study found the risk of an emergency visit increased as exposure to PM2.5, rose above 15 μg/m³ – the World Health Organization's 24-hour guideline level. Singapore experiences relatively low pollution levels compared with many heavily polluted cities, but it can also experience temporary increases during regional haze episodes.
For every 10 μg/m³ increase in PM2.5 above the reference level, the risk of an emergency visit for asthma or COPD combined rose by 3.2% over the same day and following two days. The increase was larger for asthma alone, at 4.4%.
The researchers found less certain evidence for COPD. Risk estimates increased at higher pollution levels, becoming statistically distinguishable from the reference level at around 55 μg/m³. The study also found no clear association between PM2.5 exposure and death within 30 days.
The findings suggest the effects of pollution can appear quickly. The researchers found that risk accumulated over the two days after exposure before levelling off.
The study is notable because much previous research on short-term air pollution exposure and emergency care has focused on temperate regions and places with substantially higher pollution levels. Singapore provides a different setting, with a tropical climate, relatively low average PM2.5 concentrations and occasional pollution spikes linked to transboundary haze.
The researchers analysed daily emergency department visits recorded at Singapore's public hospitals and compared them with national daily PM2.5 measurements, while accounting for factors including temperature, humidity, rainfall, seasonal patterns, holidays and the Covid pandemic period.
About 58% of the recorded emergency visits resulted in hospital admission, while 1.8% were followed by death within 30 days.
Dr Yohei Okada, corresponding author and Assistant Professor in the Prehospital and Emergency Research Centre at Duke-NUS Medical School, said: ‘Our findings show that respiratory effects can emerge even after relatively modest increases in PM2.5 and can have measurable impacts on respiratory health. This may only become apparent over the following couple of days. For people with asthma or other chronic respiratory conditions, this reinforces the importance of monitoring air quality advisories and taking precautions early rather than waiting until symptoms worsen.'
Paul Day is the editor of Healthcare Management sister title, Air Quality News.
