['Host genetic factors are thought to modulated the severity of disease caused by infection with the 2009 H1N1 pandemic influenza virus (H1N1pdm09). The human CCR5 gene encodes a cytokine receptor important for cell-mediated immune response against H1N1pdm09. A 32-bp polymorphic deletion in the coding sequence of CCR5, the so-called CCR5Δ32 allele, segregates in populations of European ancestry with a frequency of 8-15%. A high proportion of CCR5Δ32 heterozygotes was reported in a sample of white Canadian critically-ill H1N1pdm09 infected subjects, suggesting an association with disease severity.', 'We recruited 29 H1N1pdm09 infected subjects from Southern Europe (mostly Italians) with a wide clinical spectrum of disease symptoms; the sample included 7 subjects who developed acute respiratory distress syndrome requiring extracorporeal membrane oxygenation. The CCR5Δ32 variant was genotyped in all subjects.', 'The CCR5Δ32 allele was found in one single subject, who developed a very mild form and was not hospitalized.'] Is the CCR5Δ32 allele a major predisposing factor for severe H1N1pdm09 infection?