| Characteristic | Data source | |
|---|---|---|
| Sociodemographic variables | ||
| Age | <2 years versus ≥2 years | Parent |
| Sex | Male versus female | Parent |
| Age of mother at child’s birth | ≤26 years versus >26 years | Parent |
| Breastfed for ≥3 months | Yes versus no | Parent |
| Mother smokes | Yes versus no | Parent |
| Children in the home | ≥2 versus <2 | Parent |
| IMD score | High, top quintile versus quintiles 1 to 4 | Parent |
| Ethnicity | White versus mixed, Asian or Asian British, black or black British, Chinese, or other ethnic groups | Parent |
| Past medical history | ||
| Consultations for RTI in the 12 months prior to baseline | ≥2 versus <2 | General practice medical notes |
| Asthma (current diagnosis) | Yes versus No | General practice medical notes |
| Chronic conditions (any) | Yes versus No | General practice medical notes |
| Asthma (previous diagnosis) | Yes versus No | General practice medical notes |
| Parent-reported symptoms (present during the illness) | ||
| Illness duration prior to baseline (days) | <3 versus 3 | Parent |
| Breathing faster than normal | Present versus absent | Parent |
| High parent illness severity score | ≥7 versus<7 | Parent |
| Low energy/fatigue/lethargy | Present versus absent | Parent |
| Fever | Present versus absent | Parent |
| Eating less | Present versus absent | Parent |
| Illness much worse recently | Yes versus no | Parent |
| Disturbed sleep | Present versus absent | Parent |
| Wheezing or whistling in the chest | Present versus absent | Parent |
| Chills/shivering | Present versus absent | Parent |
| Taken fewer fluids/milk feeds | Present versus absent | Parent |
| Productive wet cough | Present versus absent | Parent |
| Vomiting (including after a cough) | Present versus absent | Parent |
| Passing urine less often/drier nappies | Present versus absent | Parent |
| Change in cry | Present versus absent | Parent |
| Dry cough | Present versus absent | Parent |
| Diarrhoea | Present versus absent | Parent |
| Barking/croupy cough | Present versus absent | Parent |
| Blocked/runny nose | Present versus absent | Parent |
| Parent-reported symptoms (last 24 hours) | ||
| Change in cry (moderate/severe) | Present versus absent | Parent |
| Vomiting (moderate/severe) | Present versus absent | Parent |
| Disturbed sleep (severe) | Present versus absent | Parent |
| Taking fewer fluids/milk feeds (moderate/severe) | Present versus absent | Parent |
| Passing urine less often/drier nappies (moderate/severe) | Present versus absent | Parent |
| Productive wet cough (severe) | Present versus absent | Parent |
| Chills/shivering (moderate/severe) | Present versus absent | Parent |
| Eating less (severe) | Present versus absent | Parent |
| Low energy/fatigue/lethargy (moderate/severe) | Present versus absent | Parent |
| Wheeze (moderate/severe) | Present versus absent | Parent |
| Fever (severe) | Present versus absent | Parent |
| Breathing faster than normal (moderate/severe) | Present versus absent | Parent |
| Blocked/runny nose (severe) | Present versus absent | Parent |
| Dry cough (severe) | Present versus absent | Parent |
| Barking/croupy cough (moderate/severe) | Present versus absent | Parent |
| Diarrhoea (moderate/severe) | Present versus absent | Parent |
| Clinical signs | ||
| Inter/subcostal recession | Present versus absent | Clinician |
| Bronchial breathing (unilateral/bilateral) | Present versus absent | Clinician |
| Nasal flaring | Present versus absent | Clinician |
| Pallor | Present versus absent | Clinician |
| Wheeze (unilateral/bilateral) | Present versus absent | Clinician |
| Abnormal consciousness | Yes versus no | Clinician |
| High temperature | ≥37.8°C versus <37.8°C | Clinician |
| High respiratory rate (age-related cut-offs) | Present versus absent | Clinician |
| High pulse (age-related cut-offs) | Present versus absent | Clinician |
| Inflamed pharynx | Present versus absent | Clinician |
| Grunting | Present versus absent | Clinician |
| Crackles/crepitations (unilateral/bilateral) | Present versus absent | Clinician |
| Slow capillary refill time | ≥3 seconds versus ≤2 seconds | Clinician |
| Stridor | Present versus absent | Clinician |
| High clinician illness severity score | ≥4 versus <4 | Clinician |
| Clinician gut feeling that ‘something is wrong’ | Yes versus no | Clinician |
IMD = Index of Multiple Deprivation. RTI = respiratory tract infection.