Retrospective observational study of the influence of the COVID-19 outbreak on infants' hospitalisation for acute bronchiolitis

Objectives: Acute bronchiolitis is a major public health issue with high number of infants hospitalised worldwide each year. In France, hospitalisations mostly occur between October and March and peak in December. A reduction of emergency visits for bronchiolitis has been observed at onset of the COVID-19 outbreak. We aimed to assess the pandemic effects on the hospitalisations for bronchiolitis during the 2020-2021 winter (COVID-19 period) compared with three previous winters (pre-COVID-19).

Design: Retrospective, observational and cross-sectional study.

Setting: Tertiary university paediatric hospital in Paris (France).

Participants: All infants aged under 12 months who were hospitalised for acute bronchiolitis during the autumn/winter seasons (1 October to 31 March) from 2017 to 2021 were included. Clinical and laboratory data were collected using standardised forms.

Results: During the COVID-19 period was observed, a 54.3% reduction in hospitalisations for bronchiolitis associated with a delayed peak (February instead of November-December). Clinical characteristics and hospitalisation courses were substantially similar. The differences during the COVID-19 period were: smaller proportion of infants with comorbidities (8% vs 14% p=0.02), lower need for oxygen (45% vs 55%, p=0.01), higher proportions of metapneumovirus, parainfluenzae 3, bocavirus, coronavirus NL63 and OC43 (all p≤0.01) and no influenza. The three infants positive for SARS-CoV-2 were also positive for respiratory syncytial virus, suggesting that SARS-CoV-2 alone does not cause bronchiolitis, despite previous assumptions.

Conclusion: The dramatic reduction in infants' hospitalisations for acute bronchiolitis is an opportunity to change our future habits such as advising the population to wear masks and apply additional hygiene measures in case of respiratory tract infections. This may change the worldwide bronchiolitis burden and improve children respiratory outcomes.