Because of the range of severity of recent pandemic (H1N1) 2009 infections and the possible role for CCR5 in the pulmonary immune response, we sought to determine whether patients requiring intensive care admission and respiratory support for severe pandemic (H1N1) 2009 were more likely to carry the CCR5Δ32 allele than were members of the general population. The gene discussed is CCR5; the disease is infection.