RT Journal Article SR Electronic T1 Aetiology of acute respiratory infection in preschool children requiring hospitalisation in Europe—results from the PED-MERMAIDS multicentre case–control study JF BMJ Open Respiratory Research JO BMJ Open Resp Res FD British Thoracic Society SP e000887 DO 10.1136/bmjresp-2021-000887 VO 8 IS 1 A1 Malte Kohns Vasconcelos A1 Katherine Loens A1 Louise Sigfrid A1 Elias Iosifidis A1 Cristina Epalza A1 Daniele Donà A1 Veerle Matheeussen A1 Savvas Papachristou A1 Emmanuel Roilides A1 Manuel Gijon A1 Pablo Rojo A1 Chiara Minotti A1 Liviana Da Dalt A1 Samsul Islam A1 Jessica Jarvis A1 Aggeliki Syggelou A1 Maria Tsolia A1 Maggie Nyirenda Nyang’wa A1 Sophie Keers A1 Hanna Renk A1 Anna-Lena Gemmel A1 Carmen D’Amore A1 Marta Ciofi degli Atti A1 Carmen Rodríguez-Tenreiro Sánchez A1 Federico Martinón-Torres A1 Sigita Burokienė A1 Tessa Goetghebuer A1 Vana Spoulou A1 Andrew Riordan A1 Cristina Calvo A1 Despoina Gkentzi A1 Markus Hufnagel A1 Peter J Openshaw A1 Menno D de Jong A1 Marion Koopmans A1 Herman Goossens A1 Margareta Ieven A1 Pieter L A Fraaij A1 Carlo Giaquinto A1 Julia A Bielicki A1 Peter Horby A1 Michael Sharland YR 2021 UL http://bmjopenrespres.bmj.com/content/8/1/e000887.abstract AB Background Both pathogenic bacteria and viruses are frequently detected in the nasopharynx (NP) of children in the absence of acute respiratory infection (ARI) symptoms. The aim of this study was to estimate the aetiological fractions for ARI hospitalisation in children for respiratory syncytial virus (RSV) and influenza virus and to determine whether detection of specific respiratory pathogens on NP samples was associated with ARI hospitalisation.Methods 349 children up to 5 years of age hospitalised for ARI (following a symptom-based case definition) and 306 hospital controls were prospectively enrolled in 16 centres across seven European Union countries between 2016 and 2019. Admission day NP swabs were analysed by multiplex PCR for 25 targets.Results RSV was the leading single cause of ARI hospitalisations, with an overall population attributable fraction (PAF) of 33.4% and high seasonality as well as preponderance in younger children. Detection of RSV on NP swabs was strongly associated with ARI hospitalisation (OR adjusted for age and season: 20.6, 95% CI: 9.4 to 45.3). Detection of three other viral pathogens showed strong associations with ARI hospitalisation: influenza viruses had an adjusted OR of 6.1 (95% CI: 2.5 to 14.9), parainfluenza viruses (PIVs) an adjusted OR of 4.6 (95% CI: 1.8 to 11.3) and metapneumoviruses an adjusted OR of 4.5 (95% CI: 1.3 to 16.1). Influenza viruses had a PAF of 7.9%, PIVs of 6.5% and metapneumoviruses of 3.0%. In contrast, most other pathogens were found in similar proportions in cases and controls, including Streptococcus pneumoniae, which was weakly associated with case status, and endemic coronaviruses.Conclusion RSV is the predominant cause of ARI hospitalisations in young children in Europe and its detection, as well as detection of influenza virus, PIV or metapneumovirus, on NP swabs can establish aetiology with high probability. PAFs for RSV and influenza virus are highly seasonal and age dependent.The datasets generated and analysed for this report are available from the corresponding author upon reasonable request.