2Moura FEA, Perdigao ACB, Siqueira MM. Seasonality of influenza in the tropics: a distinct pattern in Northeastern Brazil [ J]. Ame Soc Trop Med Hygiene ,2009,81 ( 1 ) : 180 - 183.
3Christoph Scholtissek. Molecular evolution of influenza viruses[J] 1995,Virus Genes(2-3):209~215