Subgroup analysis – calculated RR stratified by concentration of air pollutants and patient age
As a subgroup analysis, we calculated the RR values ​​according to the concentration of air pollutants (Table 3). From this, the concentrations of air pollutants NO2 and SO2 were not correlated with COPD exacerbation risk, nor were the environmental factors WS and SS. Only PM10 showed an increase in HR with concentration: 1.0253 at 30 µg/m3, 1.0704 at 80 µg/m3, and 1.1370 at 150 µg/m3(Table 3, Figure 3A, B).
In addition, we examined the RR values for COPD exacerbation according to patient age by time series (Table 4). Individuals aged under 20 years (preschool, school age) did not have significant RR values ​​for any of the air pollutants or environmental factors. In adults (20–59 years), PM10 at lag day 3 (which was significant from lag day 3 to 4) had an RR value of 1.0372 and NO2 at lag day 0 had a significant RR value of 1.4613. For the environmental factors, WS and SS had significant RR values ​​at lag day 0 (1.1320, 0.9444, respectively). This pattern was the same in the elderly over 60 years of age. In the case of air pollutants, PM10 at lag day 3 (which was significant from lag day 6) had an RR value of 1.0372, and NO2 at lag day 6 had a significant RR value of 1.0774. SO2 did not show significant RR values ​​in any of the age groups. For the environmental factors, WS and SS in the elderly group had significant RR values ​​at lag day 0 (1.1320 and 0.9444, respectively).