Table 3. Unadjusted and adjusted Cox-proportional hazards model for risk factors that contribute to single and recurrent episodes of childhood wheezing (n=520).

Variables	Child wheezing
	Single wheezing (n=85)				Recurrent wheezing (n=57)
	Unadjusted HR(95% CI)	P value	Adjusted HR(95% CI)	P value	Unadjusted HR(95% CI)	P value	Adjusted HR(95% CI)	P value
Child gender
Male	1.27 (0.89 to 1.82)	0.192	1.14 (0.79 to 1.65)	0.483	1.27 (0.63 to 2.54)	0.493
Female	1				1
Antenatal ETS
Yes	1.53 (1.06 to 2.22)	0.024	1.69 (1.11 to 2.56)	0.014	2.28 (1.03 to 5.06)	0.043	3.76 (1.33 to 10.66)	0.013
No	1				1
Maternal alcohol consumption
Yes	1.45 (0.83 to 2.53)	0.195	1.27 (0.74 to 2.20)	0.408	1.77 (0.68 to 4.58)	0.241	1.07 (0.34 to 3.36)	0.914
No	1				1
Family history of asthma
Yes	1.30 (0.84 to 2.01)	0.234	1.36 (0.87 to 2.14)	0.179	0.55 (0.20 to 1.57)	0.264	0.59 (0.20 to 1.72)	0.332
No	1				1
Energy sources for cooking
Biomass or fossil fuels	0.96 (0.35 to 2.59)	0.932	1.00 (0.36 to 2.76)	0.998	3.37 (1.03 to 11.05)	0.045	3.09 (0.91 to 10.45)	0.069
Electricity	1				1
Birth month NO2*	1.01 (1.00 to 1.05)	0.291	1.02 (0.99 to 1.04)	0.206	1.04 (1.00 to 1.08)	0.080	1.03 (1.00 to 1.08)	0.146
First Trimester NO2*	0.98 (0.95 to 1.01)	0.127	0.97 (0.94 to 1.00)	0.078	0.97 (0.93 to 1.03)	0.346	0.95 (0.91 to 1.01)	0.071
Birth Month PM2.5*	1.01 (0.98 to 1.05)	0.390	1.02 (0.98 to 1.05)	0.292	1.04 (0.98 to 1.11)	0.210	1.04 (0.97 to 1.10)	0.282
First Trimester PM2.5*	0.97 (0.93 to1.01)	0.166	0.96 (0.92 to 1.01)	0.077	0.94 (0.86 to 1.01)	0.106	0.95 (0.87 to 1.03)	0.186

HR is significant at α=0.05.

Bold values are statistically significant.

^*Per one unit increase of pollutant ${\displaystyle \left(\mu g/m^3\right)}$.

ETSenvironmental tobacco smokeNO₂nitrogen dioxidePM_2.5particulate matter of 2.5 µm diameter