Patient characteristics
| Factor | ≥5 MSIs | 1–4 MSIs | 0 MSIs | Overall p-value |
| Subjects | 27 | 207 | 54 | |
| MSIs during infancy# | 5 (5–6) | 2 (1–3) | 0 (0–0) | |
| Month/yr of birth | Feb 1999 to Apr 2000 | Nov 1998 to Apr 2000 | Nov 1998 to Mar 2000 | |
| Birth weight kg | 3.5±0.6 | 3.5±0.5 | 3.6±0.6 | 0.23 |
| Male | 18 (67) | 116 (57) | 27 (50) | 0.35 |
| Wheezed during infancy | 23 (85) | 65 (32) | 1 (2) | <0.0001+ |
| Wheezing episodes | 3 (1–4) | 0 (0–1) | 0 (0–0) | <0.0001+ |
| ≥1 hospitalisation for wheezing | 2/27 (7) | 5/204 (2) | 0/54 (0) | 0.15 |
| ≥1 systemic corticosteroid course | 10/27 (37) | 18/202 (9) | 0/53 (0) | <0.0001§ |
| ≥1 antibiotic treatment | 26/27 (96) | 138/204 (68) | 17/54 (31) | <0.0001ƒ |
| Atopic dermatitis during infancy | 11 (41) | 89 (44) | 22 (41) | 0.91 |
| Sensitisation at year 1 | 9 (33) | 56/198 (28) | 13/53 (25) | 0.70 |
| Food | 9 (33) | 48/198 (24) | 10/53 (19) | 0.36 |
| Aeroallergen | 5 (19) | 24/198 (12) | 6/53 (11) | 0.61 |
| Total IgE at year 1 kU·L−1 | 17.6 (7.0–31.8) | 13.6 (5.2–32.4) | 15.5 (5.6–26.8) | 0.82 |
| Blood eosinophil count¶ at year 1 ×109·L−1 | 2.0 (1.0–3.5) | 2.0 (1.0–4.0) | 2.0 (1.0–4.0) | 0.95 |
| Breast feeding | 9 (33) | 64 (31) | 18 (33) | 0.95 |
| Older sibling or day care | 27 (100) | 168 (82) | 34 (63) | 0.0002## |
| Asymptomatic infection per visit | 28/60 (47) | 20/90 (22) | 12/43 (28) | 0.0058¶¶ |
| Mixed viral infection per illness or asymptomatic visit | 36/150 (24) | 45/414 (11) | 3/187 (2) | <0.0001++ |
| Smoke exposure | 7 (26) | 54 (26) | 10 (19) | 0.48 |
| Cat at home | 9 (33) | 62 (30) | 13 (24) | 0.60 |
| Dog at home | 9 (33) | 69 (34) | 23 (43) | 0.47 |
Data are presented as median (interquartile range), n (%), mean±sd or n positive/N all studied (%), unless otherwise stated. Data analysed using one-way ANOVA, Kruskal-Wallis ANOVA or Chi-squared test. MSI: moderate-to-severe illness; Ig: immunoglobulin. #: defined as respiratory symptom score ≥5; ¶: 16 infants with ≥5 MSI, 155 infants with 1–4 MSI, 32 infants without MSI; +: ≥5 versus 1–4 MSIs and ≥5 versus 0 MSIs, p<0.0001 for both; §: ≥5 versus 1–4 MSIs (p = 0.0003), ≥5 versus 0 MSIs (p<0.0001), 0 versus 0–4 MSIs (p = 0.029); ƒ: ≥5 versus 1–4 MSIs (p = 0.0012), ≥5 versus 0 MSIs (p<0.0001), 0 versus 0–4 MSIs (p<0.0001); ##: ≥5 versus 1–4 MSIs (p = 0.018), ≥5 versus 0 MSIs (p = 0.0003); ¶¶: ≥5 versus 1–4 MSIs (p = 0.0030), ≥5 versus 0–4 MSIs (p = 0.0030), there were 193 asymptomatic scheduled visits where multiplex PCR-based assay had been carried out; ++: ≥5 versus 1–4 MSIs (p = 0.0001), ≥5 versus 0 MSIs (p<0.0001), 0 versus 1–4 MSIs (p = 0.0002).