Table 3.

Frequency (%) of chronic respiratory diseases in never-smokers in relation to toxic exposure

Characteristic	Total N = 732 (100%)	COPD N = 25 (3.4%)	P-value	Chronic bronchitis N = 86 (11.8%)	P-value
House close to a road full of cars			0.148		0.870
No	453	3.7%		12.0%
Yes	279	6.5%		12.4%
Ever lived close to a local power plant			0.637		0.178
No	536	5.1%		13.2%
Yes	196	4.1%		9.4%
Heating house by gas			0.241		0.002
No	524	5.4%		9.7%
Yes	208	2.9%		18.1%
Heating house by wood			0.133		0.018
No	550	4.0%		10.5%
Yes	182	7.5%		17.2%
Heating house by diesel			0.151		0.996
No	541	4.0%		12.2%
Yes	191	7.1%		12.2%
Heating house electrically			0.241		0.029
No	487	5.9%		14.1%
Yes	245	3.6%		8.4%
Heating house by hot air			0.154		0.589
No	669	5.4%		12.0%
Yes	63	0		14.3%
Heating house centrally			0.400		0.116
No	634	5.2%		12.9%
Yes	98	2.5%		7.3%
Cook on wood			1.000		0.190
No	681	5.1%		11.7%
Yes	51	3.1%		18.0%
Carbon monoxide in ppm M (SD)*	732	10.65 (4.48)	0.172	7.25 (4.39)	0.101

Note:

^*Mean for healthy individuals is 8.51 (SD = 5.40).

Abbreviations: COPD, chronic obstructive pulmonary disease; M, mean; SD, standard deviation.