A Trial of Placebo Versus Macrolide for Mycoplasma Pneumoniae Childhood Pneumonia: MYTHIC Study

Inclusion criteria for screening phase: * Children aged 3-17 years (from 3rd up to 18th birthday) presenting to the emergency department (ED) who will be managed ambulatory or will be admitted to general ward. * Clinical diagnosis of CAP: 1. Diagnosis defined as the treating physician's documented diagnosis of CAP; AND 2. Fever ≥38.0°C (measured by any method \[i.e., ear, axillary, rectal, or forehead site\] in the ED or via parent report observed in the last 24h); AND 3. Tachypnea (defined as respiratory rate (RR) above age-specific reference value) during the assessment in ED (triage or clinical examination). * Written screening consent for participation in screening phase signed by parents/legal guardians and the patient if ≥14 years of age. Additional inclusion criteria for intervention phase: * Positive Mp screening test result with the Mp IgM lateral flow assay (LFA) (grade 2 or 3). * Written informed consent for participation in intervention phase signed by parents or legal guardians and the patient if ≥14 years of age. Exclusion criteria: Exclusion criteria for screening phase: • None. Exclusion criteria for intervention phase: * Contraindication to azithromycin: Documented allergy to azithromycin; cardiovascular disease, including bradycardia, arrhythmias, and/or QT-interval prolongation\*; myasthenia gravis. \*Co-medication with arrhythmogenic or QT-interval-prolonging drug (www.qtdrugs.org) is no exclusion criteria but will be discussed with the local investigators and/or trial management team (TMT). * Underlying comorbidities: Cystic fibrosis or other chronic lung disorders (excluding asthma), primary or secondary immunodeficiency, sickle-cell anemia, or severe cerebral palsy. * History of recurrent pneumonia (two or more episodes) or severe pneumonia (ICU admission or complications of CAP such as lung abscess, effusion, and empyema) in lifetime. * Antibiotic treatment against Mp within the previous 7 days, including macrolides, tetracyclines, or fluoroquinolones. * Referral to ICU directly from the ED. * Inability to take oral medication. * Parents are unlikely to reliably complete follow up (FUP) visits and questionnaires (e.g., due to language barriers or living far from the study site).