The worker are the first presumed human cases of the H5 bird flu virus 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.

Four agricultural workers in southeast Washington have preliminarily tested positive for bird flu after working around an infected poultry flock at a commercial egg farm. The cases, if confirmed, would be the first time people in Washington have contracted the virus since officials began tracking a notable rise of it in birds and other animals

Four agricultural workers tested “presumptively positive” for avian influenza, or bird flu, after working with infected poultry at a commercial egg farm in Franklin County, according to the Washington State Department of Health.