Table 2.

Associations of smoking and second-hand smoke exposure status with risk of chronic obstructive pulmonary disease

	Cases	Incidence (per 10,000 person-years)	HR (95% CI)
			Model 1	Model 2
Never/Occasional smoker
Non-weekly SHS exposure	2,472	17.0	1.00	1.00
Weekly SHS exposure	3,549	16.3	1.07 (1.02, 1.14)	1.06 (1.01, 1.12)
Former smoker	406	28.2	1.19 (1.06, 1.33)	1.18 (1.05, 1.32)
Current regular smoker a	5,398	37.0	1.85 (1.74, 1.96)	1.79 (1.68, 1.90)

Cox models were stratified by 5-year age groups, sex, and study regions; model 1 was adjusted for marital status, education, household income, and occupation; model 2 was additionally adjusted for dietary habit (consumption frequency of fresh fruit, fresh vegetable, grains, and red meat), physical activity, drinking status, solid fuel use for cooking, solid fuel use for heating, stoves with chimney/extractor, body mass index, and waist circumference

HR hazard ratio, CI confidence interval, SHS second-hand smoke

^aThose who quit smoking due to illness were classified as current regular smokers