Background Interventions 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. Methods We 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. Findings The 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. Interpretation Although 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.

The authors have declared no competing interest.

https://wellcomeopenresearch.org/articles/6-120

This study received financial and administrative support from the Respiratory Syncytial Virus Consortium in Europe (RESCEU).

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The study was initially exempted from ethical review in keeping with the Control of Patient Information Notice (COPI) under a Covid-19 Notice (Regulation 3(4) of the Health Service Control of Patient Information Regulations 2002) with University Hospitals of Leicester NHS Trust as the Study Sponsor. Following a query raised about the study being adopted onto the English National Institute for Health Research (NIHR) Clinical Research Network (CRN) portfolio the study was formally reviewed by the London City and East Ethics Committee and granted permission to recruit patients without formal consent (Reference 21/REC/1844). The study is registered on ClinicalTrials.gov (NCT04959734). The use of Hospital Episode Statistics data was approved by the Health and Social Care Information Centre/NHS Digital (DARS-NIC-393510-D6H1D-v1.11). SMR01 data was provided by Public Health Scotland. Statistical disclosure control was applied to ensure patient confidentiality in line with the PHS Statistical Disclosure Protocol.

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All data produced in the present study are available upon reasonable request to the authors