The definitive diagnosis is made from isolation of the virus in culture from clinical specimens. This method not only provides the definitive diagnosis, but the viral isolate is now available for further testing, including pathogenicity, antiviral resistance, and DNA sequencing and analysis. Alternatively, antibody testing can be performed, with a standard four-fold titer increase to the specific subtype of avian influenza virus. Neutralizing antibody titer assays for H5, H7 and H9 are performed by the micorneutralization technique [72] . Western blot analysis with recombinant H5 is the confirmatory test for any positive microneutralization assay [59, 60, 72] . More recently, rapid diagnosis can be performed with reverse transcription-PCR on clinical samples with primers specific for the viral subtype [73] [74] [75] . This test should be performed only on patients meeting the case definition of possible avian influenza A infection.