Risk factors for disease severity among hospitalised patients with 2009 pandemic influenza A (H1N1) in Spain, April – December 2009 Santa-Olalla Peralta, P and Cortes-García, M and Vicente-Herrero, M and Castrillo-Villamandos, C and Arias-Bohigas, P and Pachon-del Amo, I and Sierra-Moros, M J and on behalf of the Surveillance Group for New Influenza A(H1N1) Virus Investigation and Control Team in Spain, Eurosurveillance, 15, 19667 (2010), https://doi.org/10.2807/ese.15.38.19667-en