Demographics, season of inclusion, treatment and outcome
| Groups | ARI | Control | P value |
| Total inclusions (N) | 349 | 306 | – |
| Sex (male, n, %) | 202 (57.9) | 200 (65.4) | <0.001 |
| Age in years (median, IQR) | 1.09 (0.42 to 2.49) | 1.80 (0.93 to 3.65) | <0.001 |
| Age range (n, %) | |||
| <12 months | 160 (45.9) | 83 (27.1) | <0.001 |
| 12–<36 months | 120 (34.4) | 114 (37.3) | |
| ≥36 months | 69 (19.8) | 109 (35.6) | |
| Inclusion by season (n, %) | |||
| October–December | 76 (21.8) | 85 (27.8) | <0.001 |
| January–March | 182 (52.2) | 115 (37.6) | |
| April–September | 91 (26.1) | 106 (34.6) | |
| Inclusion by country (n, %) | |||
| Greece | 144 (41.3) | 50 (16.3) | <0.001 |
| Italy | 85 (24.4) | 46 (15.0) | |
| Spain | 45 (12.9) | 45 (14.7) | |
| UK | 55 (15.8) | 94 (30.7) | |
| Other | 20 (5.7) | 71 (23.2) | |
| Symptom onset prior to inclusion in days (median, IQR) | 2 (1 to 4) | – | – |
| IVF during inpatient stay (n, %) | 184 (52.7) | – | – |
| Antibiotic treatment (n, %) | 207 (59.3) | – | – |
| PICU admission | 9 (2.6) | – | – |
| Length of hospital stay in days (median, IQR) | 3 (2 to 5) | – | – |
| Clinician diagnosis at discharge | |||
| URTI | 69 (19.8) | – | – |
| LRTI | 245 (70.2) | – | |
| Unspecified | 35 (10.0) | – | |
| Died (n, %) | 0 (0.0) | – | – |
P values were obtained using χ2 test or Wilcoxon rank-sum test as applicable.
ARI, acute respiratory infection; IQR, interquartile range; IVF, intravenous fluid; LRTI, lower respiratory tract infection; PICU, paediatric intensive care unit; URTI, upper respiratory tract infection.