Clinical Predictors of Critical Lower Respiratory Tract Illness Due to Respiratory Syncytial Virus in Infants and Children: Data to Inform Case Definitions for Efficacy Trials

We analyzed data from 524 Argentinean infants hospitalized with lower respiratory tract illness (LRTI) due to respiratory syncytial virus (RSV) to inform selection of clinical end points for RSV vaccine efficacy trials. Cases of LRTI due to RSV that required a mask, continuous or bilevel positive airway pressure, or mechanical ventilation were classified as critical. Oxygen saturation of ≤90%, tachypnea, and tachycardia were each associated with an increased odds of critical LRTI due to RSV (adjusted odds ratios [ORs], 2.30 [95% confidence interval {CI}, 1.26–4.24; P = .007], 2.22 [95% CI, 1.19–4.16; P = .012], and 2.35 [95% CI, 1.22–4.50; P = .010], respectively). The odds of critical LRTI due to RSV increased substantially (OR, 8.57; 95% CI, 2.19–73.5; P = .001) among individuals with ≥2 indicators. Lower chest wall indrawing was not associated with critical disease.