Table 1.

Case Definitions for Respiratory Tract Illness and Lower Respiratory Tract Illness Based on Those Proposed by the World Health Organization Respiratory Syncytial Virus Vaccine Consultation Expert Group [20]

Variable	Case Definition
RSV-RTI	Runny nose or blocked nose or cough AND confirmed RSV infectiona
RSV-LRTI	History of cough or difficulty breathingb AND SpO2 <95%c or RR increased AND confirmed RSV infectiona
Severe RSV-LRTI	Meeting the case definition of RSV-LRTI AND SpO2 <93%c or lower chest wall indrawing
Very severe RSV-LRTI	Meeting the case definition of RSV-LRTI AND SpO2 <90%c or inability to feed or failure to respond/being unconscious
RSV hospitalization	Confirmed RSV infectiona AND hospitalized for acute medical conditione
All-cause RTI	Runny nose or blocked nose or cough
All-cause LRTI	History of cough or difficulty breathingb AND SpO2 <95%c or RR increased

Abbreviations: LRTI, lower respiratory tract illness; RR, respiratory rate; RSV, respiratory syncytial virus; RTI, respiratory tract illness; SpO₂, blood oxygen saturation measured by pulse oximetry.

^aRSV infection confirmed on nasal swab positive for RSV-A or RSV-B subtypes by quantitative reverse-transcription polymerase chain reaction.

^bBased on history reported by parent(s)/legally acceptable representatives; difficulty breathing as evident from, eg, signs of wheezing or stridor, tachypnea, flaring of nostrils, chest indrawing, or apnea.

^cFor SpO₂, the lowest monitored value was used. At high altitudes (>2500 m), SpO₂ <92% for LRTI, <90% for severe LRTI, and <87% for very severe LRTI.

^dRR increase was defined as >60 breaths/minute (<2 months of age), >50 breaths/minute (2–11 months of age), and >40 breaths/minute (12–24 months of age).

^eHospitalization was defined as admission for observation or treatment based on the judgment of a healthcare provider.