The worker are the first presumed human cases of highly pathogenic avian influenza, H5N1, under investigation in Washington state, the Washington state Department of Health said Sunday. The workers have had mild symptoms and have been offered antiviral medication by the Benton Franklin Health District. None have required hospitalization.

Four agricultural workers in Washington state have tested positive for bird flu, the first human cases of H5N1 virus to be reported in the state. Washington is the sixth state to report a human infection of avian flu.

Officials in Washington are investigating the state’s first-ever presumed human cases of avian influenza after four agricultural workers tested presumptively positive for the disease, the