TABLE 5.

Environmental and Genetic Factors Associated With URI in the First 6 Months (n = 239 Infants)

Factor	n	HR (95% CI)	P
Cigarette exposurea	54	1.15 (0.89–1.49)	.28
Day care attendanceb	67	1.74 (1.44–2.11)	<.0001
One or more sibling(s) in the homec	86	1.07 (1.01–1.14)	.032
Breastfeeding exclusively for at least 6 mod	22	0.63 (0.40–0.99)	.049
Length of breastfeeding, moe	95	0.96 (0.93–0.99)	.0075
Length of time to exclusive formula feeding, mo	268	0.96 (0.93–0.98)	.0009
Length of time to other feeding, mof	271	0.97 (0.93–1.00)	.070
Born after February 2010g	220	0.84 (0.75–0.93)	.0012
TNFα−308 polymorphismh	81	1.19 (0.69–1.01)	.063
IL-6–174 polymorphismh	127	1.06 (0.89–1.27)	.50

CI, confidence interval

^aAny smoking in the household.

^bYes/no, any length of time.

^cLinear function, taking into account the number of siblings.

^dThe length 6 mo was chosen because it optimized the model fit to the data (ie, maximized the likelihood).

^eLength of breastfeeding, not necessarily exclusively.

^fOther food than breast milk or formula.

^gHeptavalent PCV (7) was given before February 2010; all subjects received PCV13 thereafter. Of the subjects completing the study, 73% had received 4 doses of PCV vaccines, 18% received 3 doses, 5% received 2 doses, and 3% received only 1 dose.

^hHomozygous and heterozygous.