Table 5.

Results of unadjusted and adjusted regression analysis with Cox proportional hazards model to evaluate the risk of in-hospital mortality

Variable	Univariable analysis		Multivariable analysis
	HR (95% CI)	p value	HR (95% CI)	p value
Age	1.028 (1.025–1.031)	< 0.001	1.027 (1.023–1.030)	< 0.001
Male sex	1.145 (1.065–1.230)	< 0.001	1.306 (1.212–1.407)	< 0.001
PM10 concentration increase of 1 ppm compared to previous year	0.981 (0.971–0.990)	< 0.001	0.980 (0.970–0.989)	< 0.001
Ozone concentration increase of 0.001 ppm compared to previous year	1.040 (1.017–1.064)	0.002	1.022 (0.999–1.046)	0.064
Income, decile	1.010 (1.000–1.020)	0.049	1.000 (0.991–1.010)	0.963
Charlson comorbidity index > 4	2.298 (1.881–2.809)	< 0.001	1.116 (0.898–1.387)	0.322
Disability	1.206 (1.115–1.304)	< 0.001	1.109 (1.023–1.201)	0.012
Admission to ICU due to pulmonary disorder	1.749 (1.628–1.879)	< 0.001	1.450 (1.384–1.604)	< 0.001
Admission through emergency room	0.879 (0.817–0.946)	< 0.001	0.888 (0.824–0.956)	0.002
High ICU patient volume	0.612 (0.514–0.729)	< 0.001	0.684 (0.573–0.816)	< 0.001

HR, hazard ratio; CI, confidence interval; PM10, particulate matter 10 μm or less in diameter; ppm, parts per million; ICU, intensive care unit.