Introduction
During the COVID-19 epidemic, Japan experienced an unprecedented outbreak of respiratory syncytial virus (RSV) in the summer of 2021 like other nations1), and many infants who visited hospitals were diagnosed with acute bronchiolitis. Acute bronchiolitis caused by RSV is a common disease in infants, but some cases are turned severe2). Furthermore, infants who have the RSV-induced acute bronchiolitis suffer from subsequent episodes of recurrent wheezes at a constant rate3). According to the recent reports, RSV-induced acute bronchiolitis is considered to be a trigger for the onset of childhood asthma4), and there is some concern that it may have a significant impact on the future respiratory function of patients5).
Of note, no specific treatment for acute bronchiolitis has been established. Although the efficacy of inhaled β2agonists, adrenaline and hypertonic saline and systemic steroids continues to be discussed6, 7), no satisfactory conclusions with clinical efficacy have yet been obtained. One serious problem concerning therapy for acute bronchiolitis is the difficulty of assessing the severity of acute bronchiolitis in the acute phase8), which is related to the difficulty in performing objective lung function tests, such as a spirogram, due to patient tolerance issues, as acute bronchiolitis typically has an onset under two years of age9).
Recently, the utility of a breath sound analysis as a simple, safe and non-invasive lung function test has been studied, and technological progress in this field has been remarkable10, 11). Clinically, current reports have suggested that new breath sound analyses can be used in the clinical evaluation of airway changes12), and have evaluated the lung function using breath sound analyses in children13). The possibility to objectively evaluate the airway condition in infants has also been reported 14, 15). In the present study, we have examined the characteristics of breath sounds in infants under two years old with RSV-induced acute bronchiolitis and investigated the relationship between various breath sound parameters and the severity scores and clinical symptoms in these patients.