Long-lasting effects of COVID-19 pandemic on hospitalizations and severity of bronchiolitis
Authors: Milani Gregorio Paolo , Ronchi Andrea , Agostoni Carlo , Marchisio Paola , Chidini Giovanna , Pesenti Nicola , Bellotti Anita , Cugliari Marco , Crimi Riccardo , Fabiano Valentina , Pietrasanta Carlo , Pugni Lorenza , Mosca Fabio ,   IRIDE study group, Barachetti Roberta , Pagliotta Claudia , Gulden Silvia , Risso Francesco Maria , Colpani Michael , Aversa Salvatore , Tagliabue Paolo , Cattaneo Federico , Corbetta Roberta , Ventura Maria Luisa , Ghirardello Stefano , De Lucia Ilaria , Garofoli Francesca , Mancini Luca , Pattarino Giulia Angela Carla , De Giacomo Costantino , Barberi Salvatore , Vernich Mario , Veronelli Elisabetta , Brazzoduro Emanuela , Bottino Ilaria , Varisco Tiziana , Calzi Patrizia , Porta Alessandro , Alga Paola , Cozzi Laura , Lizzoli Francesca , D’Antiga Lorenzo , Mangili Giovanna , Mazza Angelo , Di Stasio Fabiana , Marseglia Gian Luigi , Mascolo Amelia , Jankovic Matea , Decembrino Lidia , Pantaleo Dario , Vimercati Chiara , Faraguna Martha Caterina , Cattaneo Francesca , Lepri Irene , Pogliani Laura , Vimercati Chiara , Bevilacqua Liana , Bernardo Luca , Arrigoni Sergio , Mercurio Giuseppe , Paramithiotti Costanza , Salvatici Elisabetta , Banderali Giuseppe , Podestà Alberto Fabio , Dusi Elisa , Vivaldo Teresa , Bianchini Sonia , Barera Graziano , Del Barba Paolo , Aracu Claudia , Martinelli Stefano , Proto Alice , Fossati Marco , Rossi Lorella , Palumbo Emilio , Odoni Marta , Dalla Verde Ilaria , Kantar Ahmad , Sindico Paola , Morandi Grazia , Fasolato Valeria , Viscogliosi Germana , Managanelli Nunzia Pia , Riva Giuseppe , Tzialla Chryssoula , Giacchero Roberta , Sabatini Caterina , Rossi Elena , Ghitti Cesare Antonio , Pacati Ilaria , Badolato Raffaele , Dotta Laura , Meini Antonella , Bresesti Ilia , Francone Antonio , Plebani Anna Maria , Agosti Massimo , Rossi Lorella , Sala Marco , Santucci Simona , Cuzzupè Chiara , Bellan Cristina , Pontiggia Federica , Romero Alice , Perazzi Chiara , Banfi Anna , Zuccotti Gianvincenzo , Lista Gianluca 
Published: January 2024

Bronchiolitis is a common cause of hospitalization in infants. The long-lasting impact of hygiene and social behavior changes during the pandemic on this disease is debated. We investigated the prevalence of hospitalized cases, clinical severity, and underlying risk factors before and during pandemic. The study was conducted in 27 hospitals in Italy and included infants hospitalized for bronchiolitis during the following four periods: July 2018-March 2019, July 2020-March 2021, July 2021-March 2022, and July 2022-March 2023. Data on demographics, neonatal gestational age, breastfeeding history, underlying chronic diseases, presence of older siblings, etiologic agents, clinical course and outcome were collected. A total of 5330 patients were included in the study. Compared to 2018–19 (n = 1618), the number of hospitalizations decreased in 2020–21 (n = 121). A gradual increase was observed in 2021–22 (n = 1577) and 2022–23 (n = 2014). A higher disease severity (need and length of O2-supplementation, need for non-invasive ventilation, hospital stay) occurred in the 2021–22 and, especially, the 2022–23 periods compared to 2018–19. This tendency persisted after adjusting for risk factors associated with bronchiolitis severity.

   Conclusions: Compared to adults, COVID-19 in infants is often asymptomatic or mildly symptomatic and rarely results in hospitalization. This study indicates that the pandemic has indirectly induced an increased burden of bronchiolitis among hospitalized infants. This shift, which is not explained by the recognized risk factors, suggests the existence of higher infant vulnerability during the last two seasons.

What is known:• The pandemic led to a change in epidemiology of respiratory diseases• Large data on severity of bronchiolitis and underlying risk factors before and during COVID-19 pandemic are scarce

What is new:• Compared to pre-pandemic period, hospitalizations for bronchiolitis decreased in 2020–21 and gradually increased in 2021–22 and 2022–23• Compared to pre-pandemic period, higher disease burden occurred in 2021–22 and, especially, in 2022–23. This tendency persisted after adjusting for risk factors associated with bronchiolitis severity• The interplay among viruses, preventive measures, and the infant health deserves to be further investigated