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Changes in the severity and age of RSV bronchiolitis hospital admission among infants in England: a population-based birth cohort study

Presented at the Neonatal Society 2011 Autumn Meeting (programme).

Murray J, Bottle A, Sharland M, Modi N, Aylin P, Majeed A, Saxena S

Imperial College London, UK

Background: Bronchiolitis is the most common lower respiratory tract infection among infants under 1 year, typically caused by respiratory syncytial virus (RSV). To date, no national studies have reported the burden of RSV bronchiolitis hospital admissions at a population level in the UK. The aim of this study was to examine hospital admission rates for RSV bronchiolitis among term and preterm infants in England and to identify risk factors for bronchiolitis admission.

Methods: We used the Hospital Episode Statistics (HES) database to develop a population-based birth cohort with follow-up to age 1 year. We identified individual birth records from financial year April 2007 to March 2008, from 71 NHS hospitals across England (where >90% of their birth records contained complete recording of key variables, birth weight and gestational age) and linked to subsequent hospital admission records. We calculated bronchiolitis hospital admission rates among term, preterm and at-risk infants.

Results: Among our birth cohort (n=296618) there were 7189 admissions to hospital with a primary diagnosis of bronchiolitis during the first year of life, 24.2 admissions per 1000 infants under 1 year (95% CI 23.7 to 24.8). The modal age group for bronchiolitis admissions was infants aged 1 month and the median age was 120 days (IQR = 61 to 209 days). The median length of stay was 1 day (IQR = 0 to 3) and 12% (880/7189) of infants admitted with bronchiolitis were born preterm. Admission rates were higher among infants born preterm (52.9 per 1000 infants (95% CI 49.5 to 56.5)) compared with those born at term (22.5 per 1000 infants (95% CI 22.0 to 23.1)). The relative risk (RR) of a bronchiolitis admission was higher among infants with known risk factors for severe RSV infection, including those born preterm (RR 2.3 (95% CI 2.2 to 2.5)), with congenital heart conditions (RR 5.2 (95% CI 4.6 to 5.8)) or chronic lung disease (RR 2.4 (95% CI 2.1 to 2.7)), compared with healthy infants without the risk factor. Other conditions also significantly increased risk of bronchiolitis admission, including Down's syndrome (RR 6.4 (95% CI 4.2 to 9.2)) and cerebral palsy (RR 4.4 (95% CI 2.5 to 7.2)).

Conclusion: Bronchiolitis remains an important cause of hospital admissions among infants in England. Several clinical subgroups are at increased risk of admission but most infants admitted to hospital with bronchiolitis in England were born at term, with no risk factors for severe RSV infection. Our study shows infants are admitted with RSV bronchiolitis at a much earlier age than previously reported and the majority are admitted for just 1 day. These findings have implications for both active and passive immunisation policies.

Corresponding author:

1. Deshpande SA, Northern V. The clinical and health economic burden of RSV disease among children under 2 years of age in a defined geographical area. Arch Dis Child 2003 December;88(12):1065-9
2. Nair H, Nokes DJ, Gessner BD, et al. Global burden of acute lower respiratory infections due to RSV in young children: a systematic review and meta-analysis. The Lancet 2010 May 1;375(9725):1545-55
3. Hall CB, Weinberg GA, Iwane MK, et al. The Burden of Respiratory Syncytial Virus Infection in Young Children. The New England Journal of Medicine 2009 February 5;360(6):588-98.

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