1. Introduction:
Bronchiolitis is the leading cause of hospitalization in infants in high-income countries, and
respiratory syncytial virus (RSV) is the most frequent cause of the disease, accounting for 60–80% of bronchiolitis presentations [1]. RSV infection usually occurs in children by 2 years of age, and, although most have mild respiratory symptoms, it may cause severe disease mainly in infancy and early childhood [2] representing the second most frequent cause of death in infants [3].
In temperate regions, bronchiolitis shows a seasonal pattern, characterized by an increase in number in late October, a peak in January/February, and an ending in April [4].
According to epidemiological models, seasonal RSV epidemics have been shown to follow a biennial oscillation pattern, likely driven by ecological factors and a transient population-level immunity against RSV of relatively short duration (in the range of six to twelve months) [5].
The COVID-19 pandemic has drastically changed the epidemiology of acute bronchiolitis worldwide [6], requiring modifications in prevention measures and monitoring systems.
Recent literature has shown a higher incidence of bronchiolitis in the post-pandemic period, but the reports regarding disease severity are conflicting [7,8,9]. A previous study by our group showed that in our setting the number of hospitalized bronchiolitis and the need for respiratory support increased over the last five years (2017-2022), probably due to a higher prevalence of RSV infections, although no significant changes were seen regarding the need for mechanical ventilation (MV) and intensive care admissions [10].
After the 2022-2023 season, concerns have been raised for the upcoming years, as a highly unpredictable pattern in intensive care admission rates for bronchiolitis may develop, potentially threatening critical healthcare capacity [11].
This single-center retrospective observational study was designed to describe the
epidemiology, disease severity, and microbiology of bronchiolitis during the 2022-2023
season compared to the previous five years, and to characterize patients who required
intensive care support.