Table 1.

Complete inclusion and exclusion criteria

Case group	Control group
Inclusion criteria
Age <6 years old on the day of admission
Clinical suspicion of a new episode of ARI within the last 7 days	One of the following Attending for an elective or semielective procedure requiring general anaesthesia or moderate-deep sedation (including, eg, surgery, radiological examinations etc). Well and otherwise healthy children attending an outpatient clinic for a non-emergency clinical assessment.
The attending physician has decided that the child requires hospitalisation
Primary reason for hospital admission was clinical suspicion of a new episode of ARI
Temperature ≥38°C measured by any method (reported within 24 hours or at presentation)	Afebrile on the day of enrolment
And at least two of the below (with at least one of 1 or 2): Signs of lower respiratory tract infection: cough, abnormal sounds on chest auscultation (crackles, reduced breath sounds, bronchial breathing, wheezing), dyspnoea (chest indrawing, nasal flaring, grunting). Signs of upper respiratory tract infection: coryza, nasal congestion, sore throat, pharyngitis, myringitis, acute otitis media. Signs of respiratory dysfunction: tachypnoea for age or brady/apnoea or decreased oxygen saturation (<92% in room air). Signs of reduced general state: poor feeding, vomiting, lethargy/drowsiness.	No evidence of severe infection as judged by attending physician
Exclusion criteria
Inpatient care for 24 hours or more for any condition within the previous 30 days, except for routine postnatal care
Immunocompromised infant (stem cell transplant, solid organ transplant, HIV, AIDS, immunosuppressive therapy, primary immunodeficiency, haemodialysis)
Presence of complex chronic comorbidities39
Body weight <3 kg on day of assessment and/or corrected gestational age <37 weeks
Aetiology other than infection (such as trauma, autoimmune disorder, malignancy) is suspected to be the primary cause of the current illness episode	Temperature ≥38°C or <36°C
Any signs and symptoms suggesting a clear primary focus of infection, such as urinary tract infection, open wounds, indwelling catheters, reactivation of previously diagnosed infectious or inflammatory condition
Dehydration due to previous illness episode such as diarrhoea and vomiting

ARI, acute respiratory infection.