Influenza epidemics affect all age groups, although children, the elderly and those with underlying medical conditions are the most severely affected. Whereas co-morbidities are present in 50 % of fatal cases, 25-50 % of deaths are in apparently healthy individuals. This suggests underlying genetic determinants that govern infection severity. Although some viral factors that contribute to influenza disease are known, the role of host genetic factors remains undetermined. Data for small cohorts of influenza-infected patients are contradictory regarding the potential role of chemokine receptor 5 deficiency (CCR5-D32 mutation, a 32 bp deletion in the CCR5 gene) in the outcome of influenza virus infection. We tested 171 respiratory samples from influenza patients (2009 pandemic) for CCR5-D32 and evaluated its correlation with patient mortality. CCR5-D32 patients (17.4 %) showed a higher mortality rate than WT individuals (4.7 %; P50.021), which indicates that CCR5-D32 patients are at higher risk than the normal population of a fatal outcome in influenza infection. Influenza A viruses are a major source of acute respiratory infections and continue to be an important cause of acute illness and death worldwide. They cause annual epidemics and occasional pandemics with potentially fatal outcome. The mean global burden of seasonal influenza is more than 600 million cases, with 3 million cases of severe illness and almost 500 000 deaths per year worldwide (http://www. who.int/en/). A new H1N1 subtype influenza A virus emerged in 2009 [A(H1N1)pdm09], which was highly transmissible with relatively low virulence and caused the first pandemic of the 21st century (Neumann et al., 2009).Differences in disease severity can be due to pre-existing health conditions, predisposing host genetic factors, differences in the virulence of circulating viruses or a combination of these factors. The co-morbid conditions for A(H1N1)pdm09 include chronic metabolic disease, primarily diabetes mellitus and renal disease, chronic lung and cardiac disease, immunosuppressive conditions, neoplasms, obesity and pregnancy (Falagas et al., 2011; Louie et al., 2011;Singanayagam et al., 2011).Although co-morbidities are present in half of fatal cases, one-third of fatal cases have no co-morbid conditions (http://www.cdc.gov/h1n1flu/estimates_2009_h1n1.htm), suggesting that host genetic variation accounts for the distinct disease severity of A(H1N1)pdm09 infection. Several potential genetic determinants associated with A(H1N1)pdm09 infection have been described, including TNF (Antonopoulou et al., 2012), IFN-inducible transmembrane (Everitt et al., 2012), killer-cell immunoglobulin-like receptor (Aranda-Romo et al., 2012), complement regulatory protein CD55 (Zhou et al., 2012) and Toll-like receptor 3 (Esposito et al., 2012). Data relating to the role of chemokine receptor 5 (CCR5) in severe A(H1N1)pdm09-infected patients are contradictory and have been debated (Keynan et al., 2010;Rodriguez et al., 2013;Sironi et al., 2014).CCR5 regulates various aspec...