Acute Bronchiolitis in Young Children: Special Focus on Respiratory Syncytial Virus Bronchiolitis

Before 2020, India observed a predictable RSV season, with cases peaking during the rainy season and cooler months from September to February in most regions.However, the COVID-19 pandemic brought major shifts.Public health interventions such as masking, school closures, and social distancing temporarily interrupted RSV transmission and markedly reduced circulation in 2020-2021.As restrictions eased, RSV rebounded with surprising intensity and irregular timing, with several states reporting off-season surges.This loss of seasonality has led to an "immunity debt," an increased pool of susceptible children and, consequently, potentially more severe infections.These profound and unprecedented changes in RSV dynamics pose new challenges in tackling RSV. 7introDuCtion Acute bronchiolitis is the inflammation of small airways of the lower respiratory tract due to viral infection in children younger than 2 years of age.Inflammation and edema of bronchioles with excessive mucus production result in partial or complete obstruction of airways, which causes wheezing and respiratory distress.Respiratory syncytial virus (RSV) has long been a leading cause of bronchiolitis in infants and young children worldwide.Other viruses that can cause bronchiolitis include rhinovirus, parainfluenza A and B, influenza A and B, human metapneumovirus, coronavirus, and adenovirus. 1 In India, where respiratory infections continue to contribute significantly to under-5 morbidity and mortality, RSV stands out as a silent but persistent threat. 2 RSV typically presents as bronchiolitis or viral pneumonia in infants, with peak severity during the first 6 months of life.It remains a leading cause of pediatric respiratory hospital admissions, particularly among children under 2 years of age, often causing cough, wheeze, and respiratory distress that necessitate oxygen therapy or intensive care support.It also contributes to longterm pulmonary sequelae. 3 The estimated global incidence of RSV-LRTI is 48.8 per 1,000 children annually, with rates differing between developed and developing countries (24.3 vs 51.6 per 1,000, respectively), resulting in nearly 60,000 deaths among children under 5 years of age. 1,4,5 Although the exact incidence of RSV infection in India is not well defined, various studies have reported a wide range, from 2.1 to 62.4%, reflecting regional and methodological variations. 3,6,7The onset and peak of RSV infection vary seasonally across different regions.