Severe cases of bronchiolitis in children have been on the rise in recent years, and variants of the respiratory syncytial virus (RSV) responsible for the disease have contributed to the increase. This is the conclusion of a study published in the Journal of Infection by virologists from Sapienza University of Rome in collaboration with the Department of Infectious Diseases of the Istituto Superiore di Sanità.

Bronchiolitis is a disease often associated with RSV infection that can lead to respiratory failure, especially in children under one year of age. It is important to understand why some of them develop very severe clinical forms requiring hospitalisation and intensive care. The characterisation of these cases, including the identification of viral strains that cause a severe course of infection, is of paramount importance for better clinical and therapeutic management of patients and for the targeted use of prophylactic measures that are already available or will soon be available, such as monoclonal antibodies and anti-RSV vaccines.

The research, funded by a CCM project of the Ministry of Health, analysed cases of bronchiolitis admitted to the Maternity and Paediatric wards of the Umberto I General Hospital in Rome in the seasons before, during and after the pandemic, using data from the ISS's RespiVirNet surveillance platform.

The results showed that there were almost twice as many hospitalisations for RSV bronchiolitis in the autumn of 2021 compared to pre-pandemic periods, probably due to the relaxation of virus containment measures. The disease was mainly caused by RSV subtype A strains that were circulating before the COVID-19 pandemic, and the severity was similar to previous seasons. In contrast, hospitalisations for bronchiolitis in 2022-2023 were similar in number to the previous year but were mainly caused by new genetic variants of RSV subtype B, which were associated with a higher severity of disease compared to previous seasons, mainly due to the high need for respiratory support and intensive care hospitalisation.

"A strength of our research," says Guido Antonelli of Sapienza University, "is that we performed a detailed virological analysis of a large number of paediatric patients hospitalised with bronchiolitis during the last six winter seasons, from 2018-2019 to 2022-2023. All hospitalised children underwent molecular characterisation and sequencing of the RSV strain and a detailed statistical analysis of demographic and clinical data associated with an increased risk of severe forms of bronchiolitis".

"Our study", say Alessandra Pierangeli and Carolina Scagnolari, coordinators of the research carried out in close collaboration with the group of paediatricians led by Fabio Midulla and the coordination of the Department of Infectious Diseases of the Istituto Superiore di Sanità directed by Anna Teresa Palamara, "adds new elements to the understanding of the pathogenetic mechanisms associated with the RSV variants circulating in the post-pandemic period. It seems that the increased severity of disease and the increase in ICU admissions observed in cases of RSV subtype B in 2022-2023 cannot be explained solely by the immune debt associated with the lockdown periods".

"The study," emphasises Palamara, "highlights the need to strengthen national epidemiological surveillance of RSV, as well as other respiratory viruses circulating particularly in the winter months, and genomic sequencing projects integrated with studies that can monitor the infectivity and pathogenicity of viral variants. Using data such as those highlighted in this study, it is possible to predict the intensity of seasonal peaks in bronchiolitis cases, in order to rationalise healthcare resources".

Further Information

Guido Antonelli 
Department of Molecular Medicine
guido.antonelli@uniroma1.it