Table 4.

Chronic bronchitis in relation to air pollutants [particulate matter ${\mathrm{PM}}_{2.5}$, ${\text{NO}}_2$, and ${\mathrm{PM}}_{10}$] by smoking status (never/ever): odds ratios per interquartile range (IQR) increase in ${\mathrm{PM}}_{2.5}$ ($4.4{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$), ${\text{NO}}_2$ ($7.3\text{ppb}$), and ${\mathrm{PM}}_{10}$ ($5.8{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$).

Exposure and outcome	Never-smoker			Ever-smoker
	Cases	OR (95% CI)	p-Value	Cases	OR (95% CI)	p-Value	$p_{\text{Interaction}}$
${\mathrm{PM}}_{2.5}$
Incident chronic bronchitis	271	0.92 (0.77, 1.10)	0.382	367	0.95 (0.81, 1.11)	0.516	0.815
Prevalent (at baseline)
Chronic bronchitis	580	1.18 (1.04, 1.34)	0.011	771	0.96 (0.86, 1.07)	0.427	0.013
Chronic cough	1,802	1.07 (1.00, 1.15)	0.053	1,947	1.02 (0.95, 1.10)	0.545	0.345
Chronic phlegm	1,362	1.08 (1.00, 1.17)	0.059	1,414	1.00 (0.92, 1.09)	0.956	0.189
Chronic cough or phlegm	2,632	1.06 (0.99, 1.12)	0.077	2,639	1.03 (0.97, 1.10)	0.292	0.638
${\text{NO}}_2$
Incident chronic bronchitis	271	1.03 (0.91, 1.17)	0.609	367	0.97 (0.86, 1.10)	0.660	0.498
Prevalent (at baseline)
Chronic bronchitis	580	1.10 (1.01, 1.20)	0.029	771	1.00 (0.92, 1.08)	0.955	0.097
Chronic cough	1,802	1.10 (1.05, 1.16)	$<0.001$	1,947	1.01 (0.96, 1.06)	0.642	0.020
Chronic phlegm	1,362	1.07 (1.01, 1.14)	0.014	1,414	0.97 (0.92, 1.03)	0.359	0.017
Chronic cough or phlegm	2,632	1.09 (1.04, 1.13)	$<0.001$	2,639	0.99 (0.95, 1.04)	0.806	0.004
${\mathrm{PM}}_{10}$
Incident chronic bronchitis	271	1.04 (0.91, 1.18)	0.587	367	0.95 (0.83, 1.08)	0.458	0.359
Prevalent (at baseline)
Chronic bronchitis	580	1.09 (1.00, 1.20)	0.055	771	1.06 (0.98, 1.14)	0.131	0.597
Chronic cough	1,802	1.07 (1.01, 1.12)	0.015	1,947	1.02 (0.97, 1.08)	0.391	0.260
Chronic phlegm	1,362	1.10 (1.04, 1.17)	0.002	1,414	1.04 (0.98, 1.10)	0.179	0.189
Chronic cough or phlegm	2,632	1.08 (1.03, 1.13)	$<0.001$	2,639	1.02 (0.98, 1.07)	0.352	0.081

Note: For each case definition, the comparison group was all individuals without that outcome. The total number of participants with nonmissing data on all covariates was 38,006 (21,527 never-smokers and 16,479 ever-smokers) for the analysis of incident outcomes and 44,158 (24,894 never-smokers and 19,264 ever-smokers) for prevalent outcomes. Adjusted for age, race/ethnicity, body mass index, education, household income, occupational exposure to vapors/fumes or dust (ever), total pack-years, and environmental tobacco smoke exposure. Incident analysis additionally adjusted for length of follow-up time. CI, confidence interval; IQR, interquartile range; OR, odds ratio; PM, particulate matter.