Cold waves and fine particulate matter in high-altitude Chinese cities: assessing their interactive impact on outpatient visits for respiratory disease

Extreme weather events like heatwaves and fine particulate matter (PM_2.5) have a synergistic effect on mortality, but research on the synergistic effect of cold waves and PM_2.5 on outpatient visits for respiratory disease, especially at high altitudes in climate change-sensitive areas, is lacking.

we collected time-series data on meteorological, air pollution, and outpatient visits for respiratory disease in Xining. We examined the associations between cold waves, PM_2.5, and outpatient visits for respiratory disease using a time-stratified case-crossover approach and distributional lag nonlinear modeling. Our analysis also calculated the relative excess odds due to interaction (REOI), proportion attributable to interaction (AP), and synergy index (S). We additionally analyzed cold waves over time to verify climate change.

Under different definitions of cold waves, the odds ratio for the correlation between cold waves and outpatient visits for respiratory disease ranged from 0.95 (95% CI: 0.86, 1.05) to 1.58 (1.47, 1.70). Exposure to PM_2.5 was significantly associated with an increase in outpatient visits for respiratory disease. We found that cold waves can synergize with PM_2.5 to increase outpatient visits for respiratory disease (REOI > 0, AP > 0, S > 1), decreasing with stricter definitions of cold waves and longer durations. Cold waves’ independent effect decreased over time, but their interaction effect persisted. From 8.1 to 21.8% of outpatient visits were due to cold waves and high-level PM_2.5. People aged 0–14 and ≥ 65 were more susceptible to cold waves and PM_2.5, with a significant interaction for those aged 15–64 and ≥ 65.

Our study fills the gap on how extreme weather and PM_2.5 synergistically affect respiratory disease outpatient visits in high-altitude regions. The synergy of cold waves and PM2.5 increases outpatient visits for respiratory disease, especially in the elderly. Cold wave warnings and PM_2.5 reduction have major public health benefits.