The U.S. Centers for Disease Control and Prevention on Thursday confirmed two of the four presumptive positive bird flu cases among poultry farm workers in Washington state.

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.

Bird flu has possibly infected four agricultural workers in Washington state, according to the Washington State Department of Health. In a press release Sunday, the Washington State Department of Health said the “workers tested presumptively positive for avian influenza after working with infected poultry at a commercial egg farm in Franklin County.