Baseline characteristics of study subjects
| Characteristic | Cases (n=121) | Controls (n=240) | p Value |
|---|---|---|---|
| n (%)* | |||
| Age, months, median (IQR) | 21 (15–33) | 19 (11–28) | 0.97 |
| Male sex | 72 (60) | 120 (50) | 0.12 |
| No. of children in household, median (IQR) | 2 (1–2) | 2 (1–3) | 0.39 |
| Attending daycare | 91 (75) | 175 (73) | 0.77 |
| Breastfeeding | 20 (17) | 47 (20) | 0.39 |
| ≥1 parent smoking | 23 (19) | 24 (10) | 0.01 |
| Chronic diseases | 28 (24) | 9 (4) | <0.001 |
| Asthma and reactive airway disease | 21 (18) | 4 (2) | <0.001 |
| Other† | 7 (6) | 5 (2) | 0.09 |
| Ongoing antibiotic treatment | 15 (13) | 2 (1) | <0.001 |
| Antibiotic treatment last year | 55 (46) | 67 (28) | 0.002 |
| Influenza vaccination last year | 10 (9) | 1 (0.4) | 0.004 |
| Visit abroad last 3 months | 14 (12) | 53 (22) | 0.02 |
| University degree of ≥1 parent | 70 (58) | 166 (69) | 0.03 |
p Values calculated with conditional logistic regression.
*Expressed as absolute number and percentage if not otherwise specified.
†Urinary reflux, congenital heart disease, bronchopulmonary dysplasia, chromosomal abnormalities.