Influenza testing of suspected US cases of avian influenza A H5N1 reported to the Centers for Disease Control and Prevention (CDC) from February 2003 through May 2006. *Of the 37 samples tested by CDC, 35 were respiratory samples, 1 was serum, and 1 was a lung specimen. All 35 respiratory samples received by CDC were tested for human influenza by reverse transcription–PCR, and the serum sample was tested by microneutralization assay. †CDC suspected H5N1 case definition, February 2, 2004–June 7,
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