Table 3 Crude and adjusted hazard ratios for risk factors for hospitalization for lower respiratory tract infections in the first year of life

Tobacco smoke exposure

  Any

1.4 (1.0–2.1)

0.050

1.3 (0.9–1.9)

0.131

  Prenatal

    None

1

1

    Mother smoking ≤15 cigarette

1.3 (0.7–2.4)

0.476

1.0 (0.5–2.0)

0.964

    Mother smoking >15 cigarette

3.5 (1.5–8.1)

0.003

2.4 (1.0–5.7)

0.052

    Mother exposed to passive smoke

1.7 (1.1–2.6)

0.021

1.8 (1.1–2.9)

0.024

  Postnatal

    None

1

1

    Out of living environment

1.2 (0.8–1.8)

0.343

1.0 (0.6–1.5)

0.869

    In living environment

1.5 (0.7–3.1)

0.275

0.9 (0.4–1.9)

0.707

Socio demographic characteristics of parents

  Mother’s Age (y)

0.9 (0.8–1.1)

0.344

0.8 (0.7–1.0)

0.055

  Parents’ Educational Level

    Primary

1

1

    High

0.7 (0.5–1.2)

0.256

1.0 (0.6–1.7)

0.956

    Graduate

0.7 (0.4–1.3)

0.215

1.1 (0.6–2.3)

0.727

Gestational Age at birth

  Weeks

    33–34

1

1

    35–37

0.7 (0.5–1.1)

0.114

0.7 (0.4–1.0)

0.046

     > 37

0.5 (0.3–0.8)

0.002

0.5 (0.3–0.8)

0.002

Risk conditions

    Prenatal

3.4 (0.8–13.8)

0.086

2.3 (0.6–9.7)

0.242

    Perinatal

1.2 (0.7–2.2)

0.497

1.4 (0.7–2.5)

0.315

Environmental risk conditions

    Exposure to Epidemic Season

2.0 (1.3–3.0)

0.001

1.9 (1.2–2.8)

0.003

    Breastfeeding

2.0 (1.4–2.9)

0.000

1.8 (1.2–2.7)

0.003

    Siblings

3.0 (2.1–4.4)

0.000

3.2 (2.2–4.8)

0.000

    Crowded living Conditions

2.6 (1.7–4.1)

0.000

2.5 (1.6–3.9)

0.000

    Day care attendance

1.4 (0.9–2.2)

0.113

1.7 (1.1–2.7)

0.015