The clinical impact of serious respiratory disease in children under the age of two during the 2021-2022 bronchiolitis season in the United Kingdom and Ireland

BackgroundInterventions introduced in 2020 to reduce the spread of SARS-CoV-2 led to a widespread reduction in childhood infections, including respiratory syncytial virus (RSV), in the subsequent year. However, from the spring of 2021 onwards the United Kingdom and Ireland began to experience an unusual out of season epidemic of childhood respiratory disease. MethodsWe conducted a prospective observational cohort study (BronchStart), enrolling children aged 0-23 months presenting with clinician-diagnosed bronchiolitis, lower respiratory tract infection or first episode of wheeze in 59 Emergency Departments (ED) across England, Scotland and Ireland from 1 May 2021 to 30 April 2022. We collected baseline data on patient demographics and clinical presentation, and follow-up data at 7 days. We used high-granularity BronchStart clinical data together with national English and Scottish admission datasets to infer the impact of RSV disease in a typical year before the Covid-19 pandemic, and to provide an up-to-date estimate of the annual impact of disease to inform implementation of anti-RSV interventions. FindingsThe BronchStart study collected data on 17,899 ED presentations for 17,179 children. Of these, 6,825 (38.1%) were admitted to hospital for further observation or treatment, 458 (2.6%) required care in a high dependency unit (HDU), and 154 (0.9%) were admitted to a paediatric intensive care unit (PICU). Of the 5,788 children admitted and tested for RSV, 41.8% of the overall study cohort, and 48.7% of those 0-11 months of age, were positive. Risk factors for hospital admission included prematurity and congenital cardiac disease. Patients with these risk factors were also more likely to receive oxygen therapy, or be admitted to a HDU or PICU. However, 84.5% of those admitted to an observation unit, 78.1% of those admitted to a ward, 67.7% of those admitted to HDU and 50.0 % of those admitted to PICU had no identified comorbidity. Using admissions data for England and Scotland we estimate that every year 12,167 infants with RSV infection receive low flow oxygen, 4,998 high flow oxygen and 6,198 a course of antibiotic therapy in secondary care. InterpretationAlthough RSV was the major pathogen in this cohort, 51.3% of admissions for serious respiratory viral infections in those aged <1 year of age were not associated with the virus. Whilst prematurity and congenital cardiac disease were risk factors for admission to hospital, HDU and PICU, the majority of these admissions, for all levels of care except PICU, were in previously healthy term born infants.