Four new cases of bird flu were detected in farmworkers in Washington state this week. Human infections have cropping in six states as the virus spreads among farm animals.

Four farm workers who helped cull poultry on an commercial egg farm in Washington are presumed to have been infected with bird flu, making that state the sixth in the country to report human H5N1 infections this year.

Officials in Washington said four agricultural workers presumptively tested positive for avian flu, marking the first human cases of the disease in the state.