Key Points

• This review of four epidemic seasons confirms the public health burden posed by bronchiolitis outbreaks among children under 2 years of age, with 1,400 SOS Médecins calls, 5,000 emergency department visits, and 1,800 hospitalizations for bronchiolitis recorded from 2017 to 2021 in the Pays de la Loire region.

• The 2018–2019 bronchiolitis epidemic had the greatest health impact of the study period, with a higher number of emergency department visits and SOS Médecins calls for bronchiolitis in children under 2 years of age. The hospitalization rate was nevertheless comparable to that of the 2017–2018 season.

• The 2020–2021 bronchiolitis epidemic was atypical, with a longer duration (10 weeks vs. 6 to 8 weeks for the three previous seasons), a later onset than usually observed (a 13-week delay), and a peak in week 13 (vs. week 52 for the three previous seasons).

• During the 2020–2021 outbreak, a lower number of emergency department visits for bronchiolitis was observed compared to previous seasons, while the hospitalization rate for bronchiolitis was the highest in the study period. The number of SOS Médecins calls for bronchiolitis and the number of hospital samples testing positive for RSV, however, were similar.

• Bronchiolitis had a greater impact on boys during the seasons studied. Children under 2 years of age presenting to emergency departments for bronchiolitis were, on average, younger than children receiving SOS Médecins services.