Inclusion criteria:  Admission to the pediatric ICU with a confirmed diagnosis of RSV infection. RSV infection is based on a positive nasal swab for RSV fluorescent antibody or via multiplex assay or culture; Requiring intensive respiratory support defined as either mechanical ventilation or NIV (BiPAP or CPAP) or HFNC (at >1 L/kg/min of flow, with a minimum of 5L/min flow for children <5 kg); Enrollment into the study within 48 hours of ICU admission and placement on intensive respiratory support; Age: Neonates-2 years. For those less than 1 week of age, they must have been discharged home from the hospital after their birth.  Exclusion criteria:  AZM use within 7 days of ICU admission; Contraindication to AZM use including known hypersensitivity to AZM, erythromycin, any macrolide, or ketolide drug, patients with significant hepatic impairment (direct bilirubin >1.5 mg/dL); Patients with known cardiac disease, cardiac arrhythmia or with electrocardiogram QT interval corrected for heart rate (QTc) ≥ 450 milisecond (ms); Intensive respiratory support greater than 48 hours prior to ICU admission; Chronic ventilation or supplemental oxygen need at home; Immunosuppressive conditions such as those post heart or hematopoietic stem cell transplant or receiving chemotherapy and chronic steroids; History of pyloric stenosis; AZM is deemed necessary for clinical treatment (for instance, if patient has pertussis).