[Acute impact of persistent high ambient fine particulate matter exposures on hospital visits for respiratory diseases from 2013 to 2018 in the Beijing-Tianjin-Hebei region and surrounding areas].

Objective: To investigate the acute effects of persistent high exposure to atmospheric fine particulate matter (PM_2.5) on residents' outpatient visits for respiratory diseases. Methods: We collected daily outpatient records from 92 hospitals in 13 cities across the Beijing-Tianjin-Hebei region, along with daily PM_2.5, nitrogen dioxide (NO₂), and meteorological data from 2013 to 2018. Five persistent high PM_2.5 exposure scenarios were defined in terms of daily mean PM_2.5 concentrations (>75 μg/m³ and >150 μg/m³), duration (≥2 days and ≥3 days), and whether or not there was concurrent exposure to high levels of NO₂ (daily mean NO₂ concentration >50 μg/m³). A two-stage statistical analysis strategy based on a generalized linear model was applied to conduct a time-series analysis to assess the exposure-response relationship between persistent high PM_2.5 exposure scenarios and residents' outpatient visits for a variety of respiratory diseases, and to estimate excess outpatient visits. Results: During the period, M (Q₁, Q₃) PM_2.5 and NO₂ concentrations were 61.2 (42.3, 95.1) μg/m³ and 40.2 (31.4, 54.4) μg/m³, respectively, and the daily respiratory disease outpatient visits were 57 (52, 66) cases. When compared with non-permanent high PM_2.5 exposure periods, exposure scenarios with PM_2.5 >75 μg/m³ and lasting for ≥2 days caused an increased risk of outpatient visits for respiratory diseases by 2.10% (95%CI: 1.44%-2.77%), and resulted in 43 787 (95%CI: 30 025-57 757) excess visits; in this scenario, the concurrent exposure to high levels of NO₂ had a greater acute effect on respiratory disease visits than the absence of exposure to high levels of NO₂ (P<0.001). The risk of respiratory disease visits increased substantially by 4.41% (95%CI: 3.15%-5.68%) when the daily mean PM_2.5 concentration exceeded 150 μg/m³ for ≥2 days. Subgroup disease analyses showed that scenarios with daily mean PM_2.5 concentrations exceeding 75 μg/m³ for ≥3 days caused a significant increase in the risk of lower respiratory tract infections, chronic lower respiratory disease, and asthma visits. Conclusions: Sustained persistent high PM_2.5 exposure increases the risk of outpatient visits for various respiratory diseases; concurrent exposure to high concentrations of NO₂ leads to a greater risk of visiting the clinic, suggesting that the prevention and control of PM_2.5 pollution should be synchronized with the control of mobile source emissions, to synergistically manage the compound pollution of PM_2.5 and NO₂ in the atmosphere.