“Riddles” of acute bronchiolitis; «Загадки» острого бронхиолита

The most common infectious disease of the lower respiratory tract in infants is acute bronchiolitis (AB). AB affects the bronchioles - a part of the respiratory tract between the bronchi and alveoli, so the disease has features of both bronchitis and pneumonia, which may be associated with difficulties in establishing a diagnosis and underdiagnosis in real clinical practice. The review, based on current literature data, research results and the authors' experience, presents modern information on the etiology, epidemiology, risk factors, pathogenesis, pathomorphology, clinical picture, and diagnosis of AB. Approaches to therapy and prevention of the disease are outlined from the standpoint of evidence-based medicine. The outcomes and consequences of acute bronchiolitis are described separately. © 2025 Elsevier B.V., All rights reserved.