Table 1.

Study definitions and eligibility criteria

Definitions
Fast breathing for age	Children 2 to <12 months of age: RR ≥50 breaths per minute Children≥12 months of age: RR ≥40 breaths per minute
Severe respiratory distress	Grunting, nasal flaring and/or head nodding
WHO IMCI general danger signs	Lethargy or unconsciousness, convulsions, vomiting everything, inability to drink or breastfeed
Eligibility criteria
Inclusion criteria	Cases 2 through 23 months of age Cough <14 days or difficulty breathing Visible indrawing of the chest wall with or without fast breathing for age Ability and willingness of child’s caregiver to provide informed consent and to be available for follow-up for the planned duration of the study, including accepting a home visit if he/she fails to return for a scheduled study follow-up visit Controls 2 through 23 months of age Cough <14 days or difficulty breathing Ability and willingness of child’s caregiver to provide informed consent and to be available for follow-up for the planned duration of the study, including accepting a home visit if he/she fails to return for a scheduled study follow-up visit
Exclusion criteria	Cases Resolution of chest indrawing after bronchodilator challenge, if wheezing at screening examination Severe respiratory distress Arterial SpO2 <90% in room air, as assessed non-invasively by a pulse oximeter WHO IMCI general danger signs Stridor when calm Known or possible tuberculosis (history of a cough ≥14 days) Any medical or psychosocial condition or circumstance that, in the opinion of the investigators, would interfere with the conduct of the study or for which study participation might jeopardise the child’s health Living outside the study catchment area Controls Axillary temperature ≥38°C Fast breathing for age Visible indrawing of the chest wall SpO2 <95% in room air, as assessed non-invasively by a pulse oximeter WHO IMCI general danger signs Stridor when calm Known or possible tuberculosis (history of a cough ≥14 days) Any medical or psychosocial condition or circumstance that, in the opinion of the investigators, would interfere with the conduct of the study or for which study participation might jeopardise the child’s health Living outside the study catchment area

IMCI, Integrated Management of Childhood Illnesses; RR, respiratory rate; SpO₂, oxyhaemoglobin saturation.