Table 2.

Associations between secondhand smoke (SHS) exposure and serum cotinine level (ng/mL) among US adult smokers (ages ≥20), with stratification by smoking intensities, USA, 1999–2012

	All adult smokers (n=4547)				Light smokers* (n=2130)		Moderate/heavy smokers*(n=2417)
	Unadjusted β (95% Cl)	p Value	Adjusted† β (95% Cl)	p Value	Adjusted† β (95% Cl)	p Value	Adjusted† β (95% Cl)	p Value
SHS exposure
SHS exposure at work (reference=none)	0.132 (0.011 to 0.253)	0.032	0.065 (−0.025 to 0.154)	0.154	0.165 (−0.022 to 0.353)	0.084	−0.009 (−0.081 to 0.064)	0.814
SHS exposure at home (reference=none)	0.806 (0.699 to 0.913)	<0.001	0.483 (0.353 to 0.614)	<0.001	0.239 (0.098 to 0.380)	0.001	0.146 (0.083 to 0.208)	<0.001
Smoking behaviours
Mean cigarettes per day in previous 5 days (unit=1 cigarette per day)	0.066 (0.060 to 0.072)	<0.001	0.038 (0.032 to 0.446)	<0.001	–	–	–	–
Number of days smoked cigarettes in previous 5 days (unit=1 day smoked)	0.810 (0.753 to 0.866)	<0.001	0.578 (0.507 to 0.649)	<0.001	0.582 (0.510 to 0.654)	<0.001	0.291 (0.045 to 0.538)	0.021
Most recent cigarette smoked on the same day of examination (reference=most recent cigarette smoked 1–4 days before the examination)	1.508 (1.358 to 1.658)	<0.001	0.090 (0.021 to 0.201)	0.112	0.254 (0.096 to 0.412)	0.002	0.082 (−0.084 to 0.249)	0.329
Demographics
Age (10 years interval)	0.168 (0.130 to 0.206)	<0.001	0.059 (0.032 to 0.087)	<0.001	0.109 (0.061 to 0.158)	<0.001	0.038(0.017 to 0.059)	<0.001
Gender (reference=male)	−0.005 (−0.095 to 0.084)	0.906	−0.055 (−0.128 to −0.018)	0.137	−0.086 (−0.239 to 0.068	0.273	−0.084 (−0.133 to −0.029)	0.003
Education (reference=less than high school)
High school graduate or equivalent	0.028 to 0.063–0.119	0.545	−0.009 (−0.081 to 0.062)	0.793	−0.001 (−0.177 to 0.177)	0.997	−0.011 (−0.067 to 0.046)	0.713
Some college	−0.369 (−0.482 to −0.257)	<0.001	−0.103 (−0.169 to 0.037)	0.002	−0.108 (−0.250 to 0.034)	0.136	−0.084 (−0.160 to −0.008)	0.032
Race/ethnicity (reference=non-Hispanic white)
Non-Hispanic black	0.271 (−0.167 to 0.375)	<0.001	0.382 (0.307 to 0.456)	<0.001	0.471 (0.335 to 0.607)	<0.001	0.214 (0.141 to 0.287)	<0.001
Mexican American	−1.418 (−1.621 to −1.215)	<0.001	−0.574 (−0.731 to −0.416)	<0.001	−0.685 (−0.894 to −0.476)	<0.001	−0.184 (−0.297 to −0.071)	0.002
Other Hispanic	−0.733 (−0.951 to −0.516)	<0.001	−0.246 (−0.405 to −0.087)	0.003	−0.331 (−0.567 to −0.094)	0.007	−0.015 (−0.099 to 0.068)	0.715
Mixed race/other	−0.384–0.639 to −0.129)	0.004	−0.128 (−0.284 to 0.028)	0.106	−0.273 (−0.561 to 0.014)	0.062	−0.007 (−0.073 to 0.087)	0.870
Interaction
Cigarettes per day × home SHS exposure	–	–	−0.025	<0.001	–	–	–	–

Bolded values represent significance of the p Value <0.05.

^*Light smokers smoked 1–9 cigarettes per day on average over the previous 5 days, moderate/heavy smokers smoked 10+ cigarettes per day on average over the previous 5 days.

^†Models adjusted for all covariates listed in the table as well as survey year (not shown).