Introduction:
Acute lower respiratory infection (ALRI), comprising both bronchiolitis and pneumonia, is a global leading cause of morbidity and hospital admissions of infants and young children, with respiratory syncytial virus (RSV) being a major viral cause. Guidelines recommend a clinical diagnosis of bronchiolitis but do not advise how to distinguish between different viral aetiologies using clinical, laboratory, and radiological criteria.

Aim of the study:
The aim of this study was to provide clinical data that characterise RSV and non-RSV aetiology of bronchiolitis for the purpose of better defining the correlations between the viral aetiology and clinical characteristics as well as the risk factors of severe disease.

Material and methods:
We retrospectively reviewed 135 records of 116 infants and young children who were hospitalised due to bronchiolitis during one infectious season. A detailed analysis of patients’ medical history, clinical course of bronchiolitis, viral aetiology of infection, basic laboratory tests, as well as radiological findings was performed.

Results:
Children with RSV bronchiolitis more frequently demonstrated obstruction of the lower airways manifesting with diminished breath sounds and crackles on auscultation and more severe course of the disease than non-RSV patients, defined as hypoxaemia and desaturation, the need for supplemental oxygen, longer duration of oxygen therapy, and a longer hospitalisation.

Conclusions:
Clinical symptoms of obstruction of lower airways are more frequent and more severe in RSV than in non-RSV bronchiolitis. Because basic laboratory tests and chest radiographs are not helpful in distinguishing between RSV and non-RSV bronchiolitis, their use in uncomplicated cases should be limited. Therefore, careful clinical assessment and monitoring of children with bronchiolitis is of utmost importance in predicting the course of ALRI and in the implication of therapeutic decisions.