The CDC is deploying a team to Washington state to assess the health of farm workers who culled poultry suffering from bird flu after four workers are presumed to have been infected by the virus, U.S.

All of the state's cases have been linked to contact with infected dairy cows, officials said. No human-to-human transmission has been documented.

During the monitoring period, after the seasonal influenza period had ended, 59 wastewater treatment plants showed increases in the H5 gene in bird flu that coincided with the recorded emergence of highly pathogenic avian influenza H5N1 in dairy cattle.

Bird flu is presumed to have infected four poultry workers in Washington state, making it the sixth U.S. state to identify human cases this year, according to the Washington State Department of Health.

However, there is urgent concern over dairy cows. In California’s Central Valley, the carcasses of dead cattle have been piling up, a phenomenon documented in videos taken by a local veterinarian. According to the CDC, there have been confirmed infections in more than 300 herds of cattle in the U.S. in 14 states since March.

Washington state health officials are investigating after four agricultural workers tested presumptively positive for bird flu, marking the first presumed human cases in the state, the Washington State Department of Health announced Sunday.

In this photo provided by the U.S. Department of Agriculture, a researcher performs a rapid antigen test on milk from a dairy cow inoculated against bird flu in a containment building at the National Animal Disease Center research facility in Ames, Iowa, on Monday, July 29, 2024.

Cows in California are dying at much higher rates from bird flu than in other affected states, industry and veterinary experts said, and some carcasses have been left rotting in the sun as rendering plants struggle to process all the dead animals.

Four people have reportedly developed symptoms of avian influenza after working with infected poultry in Franklin County.