Washington state officials identify four new cases of bird flu, as H5N1 outbreak spreads

800,000 birds were killed in the wake of presumptive positive tests

Four people in Washington state are suffering from bird flu, prompting fears about the illness spreading to other agricultural workers in the U.S.

Also known as avian influenza A (H5N1), the disease recently tested presumptively positive in four agricultural workers in Washington state, according to the Washington State Department of Health (WADOH). The press release noted that the workers are employed on an egg farm in Franklin County.

"The individuals experienced mild symptoms and have been provided with antiviral medication," the statement read. "Testing of additional individuals on the farm is currently pending and the number of cases under investigation may change."

Washington state officials noted that these diagnoses mark the "first presumed human cases of H5 virus under investigation in Washington state." In response, more than three quarters of a million birds were killed.

"About 800,000 birds were euthanized after test results by the Washington State Department of Agriculture on Oct. 15 showed that they were infected with avian influenza," the statement read.

Washington state is the sixth U.S. state to identify a human infection of H5N1, which is a highly pathogenic avian influenza that has been detected in poultry, dairy cattle and wildlife.