Box 1.

: Definitions for recruitment

• Patients aged ⩾16 years who were previously well and not under supervision or management for an underlying disease (for example, no pre-existing asthma, chronic obstructive pulmonary disease, heart disease, and diabetes)

• Lower respiratory tract illness required all of:Acute illness present for 21 days or lessCough as the main symptomAt least one other lower respiratory tract symptom (sputum production, dyspnoea, wheeze, chest discomfort or pain)No alternative explanation (for example, not sinusitis, pharyngitis, a new presentation of asthma)