Association of risk factors with wheeze in the second year of life: demographics, birth details, familial allergic disease, living environment and maternal education
| Unexposed % (n/N) | Exposed % (n/N) | Wheeze in unexposed % (n/N) | Wheeze in exposed % (n/N) | Unadjusted IRR (95% CI) (P value) | Primary model –adjusted IRR (95% CI) (P value) (n=3612) | Sensitivity model 1 – adjusted IRR (95% CI) (P value) (n=4227) | |
| Basic demographics and birth details | |||||||
| Male gender (vs female) | 48.6 (4263/8774) | 51.4 (4511/8774) | 6.6 (280/4263) | 8.9 (401/4511) | 1.35 (1.16 to 1.58) (<0.001) | 1.33 (1.03 to 1.70) (0.027) | 1.32 (1.06 to 1.64) (0.014) |
| Gestation (per week increase) | 1.04 (0.99 to 1.10) (0.105) | 1.02 (0.93 to 1.12) (0.700) | |||||
| Birth weight (per kg increase) | 1.24 (1.07 to 1.44) (0.004) | 0.88 (0.60 to 1.28) (0.495) | |||||
| Birth length (per cm increase) | 0.96 (0.94 to 0.99) (0.004) | 0.99 (0.92 to 1.06) (0.715) | |||||
| Apgar score at 5 min (per 1 point increase) | 0.94 (0.84 to 1.053) (0.282) | ||||||
| Multiple birth (vs single birth) | 97.9 (8577/8760) | 2.1 (183/8760) | 7.7 (663/8577) | 8.7 (16/183) | 1.13 (0.69 to 1.86) (0.626) | ||
| Caesarean delivery (vs vaginal delivery) | 75.4 (6587/8731) | 24.6 (2144/8731) | 7.7 (506/6587) | 8.1 (173/2144) | 1.05 (0.88 to 1.25) (0.577) | ||
| Non-Caucasian mother (vs Caucasian mother) | 95.4 (8330/8734) | 4.6 (404/8734) | 7.7 (640/8330) | 9.9 (40/404) | 1.29 (0.94 to 1.77) (0.120) | ||
| Non-Caucasian father (vs Caucasian father) | 94.8 (8255/8708) | 5.2 (453/8708) | 7.5 (622/8255) | 11.9 (54/453) | 1.58 (1.20 to 2.09) (0.001) | 1.44 (0.85 to 2.44) (0.180) | |
| Maternal age (per 1 year increase) | 1.00 (0.98 to 1.01) (0.691) | ||||||
| Paternal age, years (per 1 year increase) | 1.00 (0.99 to 1.01) (0.918) | ||||||
| Familial allergic disease | |||||||
| Maternal self-reported, doctor-diagnosed allergic disease | |||||||
| Any (yes vs no) | 73.7 (6435/8732) | 26.3 (2297/8732) | 6.0 (386/6435) | 12.6 (290/2297) | 2.11 (1.81 to 2.45) (<0.001) | 1.13 (0.84 to 1.52) (0.428) | |
| Asthma (yes vs no) | 90.8 (809/8760) | 9.2 (809/8760) | 6.8 (544/7951) | 16.7 (135/809) | 2.44 (2.02 to 2.95) (<0.001) | 1.30 (0.90 to 1.87) (0.158) | 1.47 (1.12 to 1.93) (0.006) |
| Allergic rhinitis (yes vs no) | 84.8 (7418/8749) | 15.2 (1331/8749) | 6.9 (511/7418) | 12.5 (166/1331) | 1.81 (1.52 to 2.16) (<0.001) | ||
| Eczema (yes vs no) | 88.1 (7706/8748) | 11.9 (1042/8748) | 7.0 (537/7706) | 13.4 (140/1042) | 1.93 (1.60 to 2.32) (<0.001) | ||
| Paternal self-reported, doctor-diagnosed allergic disease | |||||||
| Any (yes vs no) | 78.7 (6811/8652) | 21.3 (1841/8652) | 6.3 (427/6811) | 12.7 (234/1841) | 2.03 (1.73 to 2.38) (<0.001) | 1.32 (0.98 to 1.78) (0.067) | 1.31 (1.04 to 1.65) (0.020) |
| Asthma (yes vs no) | 92.9 (8083/8699) | 7.1 (616/8699) | 7.1 (571/8083) | 15.4 (95/616) | 2.18 (1.76 to 2.71) (<0.001) | 0.73 (0.46 to 1.15) (0.174) | |
| Allergic rhinitis (yes vs no) | 85.7 (7415/8657) | 14.4 (1242/8657) | 7.1 (528/7415) | 11.2 (139/1242) | 1.58 (1.30 to 1.90) (<0.001) | ||
| Eczema (yes vs no) | 93.8 (8153/8688) | 6.2 (535/8688) | 7.2 (587/8153) | 14.8 (79/535) | 2.05 (1.62 to 2.60) (<0.001) | ||
| Living environment | |||||||
| Rural housing (vs urban housing) | 83.8 (7352/8774) | 16.2 (1422/8774) | 7.9 (580/7352) | 7.1 (101/1422) | 0.90 (0.73 to 1.11) (0.330) | ||
| Mould in house (yes vs no) | 90.2 (7667/8503) | 9.8 (836/8503) | 7.5 (573/7667) | 9.5 (79/836) | 1.26 (1.00 to 1.60) (0.051) | 0.96 (0.64 to 1.44) (0.833) | |
| Pets | |||||||
| Any (yes vs no) | 63.9 (5594/8751) | 36.1 (3157/8751) | 7.8 (438/5594) | 7.6 (241/3157) | 0.98 (0.83 to 1.14) (0.752) | ||
| Cat (yes vs no) | 84.6 (7398/8751) | 15.5 (1353/8751) | 7.7 (566/7398) | 8.4 (113/1353) | 1.09 (0.89 to 1.34) (0.395) | ||
| Dog (yes vs no) | 83.9 (7343/8751) | 16.1 (1408/8751) | 8.3 (606/7343) | 5.2 (73/1408) | 0.63 (0.49 to 0.80) (<0.001) | 0.90 (0.60 to 1.33) (0.587) | |
| Maternal education | |||||||
| Basic not completed | 1.16 (0.77 to 1.74) (0.483) | ||||||
| Basic completed | Baseline comparator | ||||||
| Junior college/vocational | 1.15 (0.91 to 1.45) (0.255) | ||||||
| College/university | 1.20 (0.96 to 1.50) (0.114) | ||||||
Primary model: includes all variables with P<0.1 in univariate analysis (gender, gestation, birth weight, birth length, ethnicity of father, maternal allergy, maternal asthma, paternal allergy, paternal asthma, mould in house, dog ownership, day care attendance, respiratory tract infections and eczema), plus food allergy, variables related to feeding and smoke exposure and study centre.
Sensitivity model 1: This was generated by applying backward deletion to the primary model. It includes overlap of breast feeding/solids, mother smoking at 1-year follow-up, gender, day care attendance, LRTIs, eczema and study centre.
IRR, incidence rate ratio; LRTIs, lower respiratory tract infections; URTIs, upper respiratory tract infections.