Increased bronchiolitis burden and severity after the pandemic: a national multicentric study

Background: The coronavirus 2019 (COVID-19) related containment measures led to the disruption of all virus distribution. Bronchiolitis-related hospitalizations shrank during 2020-2021, rebounding to pre-pandemic numbers the following year. This study aims to describe the trend in bronchiolitis-related hospitalization this year, focusing on severity and viral epidemiology. Methods: We conducted a retrospective investigation collecting clinical records data from all infants hospitalized for bronchiolitis during winter (1st September-31th March) from September 2018 to March 2023 in six Italian hospitals. No trial registration was necessary according to authorization no.9/2014 of the Italian law. Results: Nine hundred fifty-three infants were hospitalized for bronchiolitis this last winter, 563 in 2021-2022, 34 in 2020-2021, 395 in 2019-2020 and 483 in 2018-2019. The mean length of stay was significantly longer this year compared to all previous years (mean 7.2 ± 6 days in 2022-2023), compared to 5.7 ± 4 in 2021-2022, 5.3 ± 4 in 2020-2021, 6.4 ± 5 in 2019-2020 and 5.5 ± 4 in 2018-2019 (p < 0.001), respectively. More patients required mechanical ventilation this winter 38 (4%), compared to 6 (1%) in 2021-2022, 0 in 2020-2021, 11 (2%) in 2019-2020 and 6 (1%) in 2018-2019 (p < 0.05), respectively. High-flow nasal cannula and non-invasive respiratory supports were statistically more common last winter (p = 0.001 or less). RSV prevalence and distribution did not differ this winter, but coinfections were more prevalent 307 (42%), 138 (31%) in 2021-2022, 1 (33%) in 2020-2021, 68 (23%) in 2019-2020, 61 (28%) in 2018-2019 (p = 0.001). Conclusions: This study shows a growth of nearly 70% in hospitalisations for bronchiolitis, and an increase in invasive respiratory support and coinfections, suggesting a more severe disease course this winter compared to the last five years.