Health officials are investigating the first presumed human cases of bird flu in Washington state after four agricultural workers tested positive for H5N1 last week. Why it matters: These are Washington's first presumed human cases of avian flu,

Four agricultural workers tested presumptively positive for avian influenza after working with infected poultry at a commercial egg farm.

Four agricultural workers in Washington state tested presumptively positive for avian influenza while working at a farm with an outbreak.