​Four human cases of highly pathogenic avian influenza (HPAI) A(H5) (“H5 bird flu”) virus infection in the state of Colorado have been confirmed by the Centers for Disease Control and Prevention (CDC). Four human cases of highly pathogenic avian influenza (HPAI) A(H5) (“H5 bird flu”) virus infection in the state of Colorado have been confirmed by the Centers for Disease Control and Prevention (CDC).