Table 3.

Risk factors for 667 contacts to have latent TB infection

Variates	No. of LTBI casesa in each category of the contact (%)	Univariable			Multivariable
		OR	95% CI	P value	Adjusted OR	95%CI	P value
Contacts of index caseb
No	222/565 (39.3)	1.0			1.0
Yes	80/102 (78.4)	5.6	3.4‐9.3	<.0001	4.9	2.9‐8.1	<.0001
Contact under CO2 level >1000 ppm
No	57/179 (31.8)	1.0			1.0
Yes	45/488 (50.2)	2.2	1.5‐3.1	<.0001	1.6	1.1‐2.3	.014

Abbreviations: CO₂, carbon dioxide; LTBI, latent TB infection; OR, odds ratio; ppm, parts per million; TB, tuberculosis.

^aNumber of latent TB infection cases, defined as a positive tuberculin skin test using a cutoff point of 10 mm.

^bAll 102 contacts of the index case were exposed under poorly ventilated environment (CO₂ levels >1000 ppm).