Aetiology of acute respiratory infection in preschool children requiring hospitalisation in Europe-results from the PED-MERMAIDS multicentre case-control study by Kohns Vasconcelos, M, Loens, K, Sigfrid, L, Iosifidis, E, Epalza, C, Donà, D, Matheeussen, V, Papachristou, S, Roilides, E, Gijon, M, Rojo, P, Minotti, C, Da Dalt, L, Islam, S, Jarvis, J, Syggelou, A, Tsolia, M, Nyirenda Nyang'wa, M, Keers, S, Renk, H, Gemmel, A-L, D'Amore, C, Ciofi Degli Atti, M, Rodríguez-Tenreiro Sánchez, C, Martinón-Torres, F, Burokienė, S, Goetghebuer, T, Spoulou, V, Riordan, A, Calvo, C, Gkentzi, D, Hufnagel, M, Openshaw, PJ, de Jong, MD, Koopmans, M, Goossens, H, Ieven, M, Fraaij, PLA, Giaquinto, C, Bielicki, JA, Horby, P, Sharland, M