I. Confirmation standard of Influenza A (H1N1) cases: Patients are considered to have contracted the virus if they present with influenza-like clinical manifestations and had one or more of the following laboratory test results: (1) Positive for S-OIV nucleic acid (through real-time RT-PCR and RT-PCR); (2) S-OIV is isolated and attained; and (3) Specific neutralizing antibody titers for serum S-OIV are increased four times or more.