Table 5.

Risk ratios ratios (RRRs) and 95% confidence intervals (CIs) from multinomial logistic regression models between air pollution at residence and severity of COVID-19 disease among the total COVICAT population and subgroups with serological testing and positive antibodies for SARS-CoV-2 infection.

Population/air pollutant	Mild cases	Severe/critical cases
	RRR (95% CI)a	RRR (95% CI)a
Total population ($n=\mathrm{9,605}$: 9,124 noncases, 413 mild cases, 68 severe/critical cases)
${\mathrm{NO}}_2$	1.12 (0.97, 1.30)	1.26 (0.89, 1.79)
${\mathrm{PM}}_{2.5}$	1.13 (0.98, 1.30)	1.51 (1.06, 2.16)
BC	1.02 (0.90, 1.17)	0.84 (0.62, 1.15)
${\mathrm{O}}_3$	0.94 (0.83, 1.06)	0.81 (0.59, 1.11)
Participants with serology ($n=\mathrm{4,103}$: 3,918 noncases, 160 mild cases, 25 severe/critical cases)
${\mathrm{NO}}_2$	1.27 (1.01, 1.61)	1.83 (1.01, 3.31)
${\mathrm{PM}}_{2.5}$	1.24 (0.98, 1.57)	2.12 (1.13, 3.96)
BC	0.95 (0.77, 1.17)	1.21 (0.70, 2.09)
${\mathrm{O}}_3$	0.84 (0.68, 1.04)	0.59 (0.33, 1.06)
Participants with SARS-CoV-2 infection ($n=743$: 622 noncases, 100 mild cases, 21 severe/critical cases)
${\mathrm{NO}}_2$	1.18 (0.85, 1.65)	1.84 (0.94, 3.58)
${\mathrm{PM}}_{2.5}$	1.13 (0.80, 1.59)	2.03 (0.99, 4.17)
BC	1.05 (0.79, 1.39)	1.21 (0.68, 2.16)
${\mathrm{O}}_3$	0.94 (0.70, 1.25)	0.59 (0.31, 1.14)

Note: Associations reported per interquartile range. Severe COVID-19 was defined as having been admitted to the hospital or ICU, or having had oxygen therapy without having been admitted to the hospital. Mild cases included any other COVID-19 case. Noncases were the reference group. BC, black carbon; COVICAT, COVID-19 cohort in Catalonia study; ICU, intensive care unit; ${\mathrm{NO}}_2$, nitrogen dioxide; ${\mathrm{O}}_3$, ozone; ${\mathrm{PM}}_{2.5}$, particulate matter.

^a Adjusted for age, sex, education (less than primary/primary/secondary/university), 2011 census deprivation index (quintiles), population density and type of survey (online/telephone).