Four agricultural workers in Washington state may be infected with highly pathogenic avian influenza, commonly known as bird flu, the Washington State Department of Health stated on Oct. 20.

The four cases emerged at a farm that was the site of an avian influenza outbreak in chickens earlier this month, according to the Department of Health.

Roughly 800,000 birds at the same farm were euthanized after test results by the Washington State Department of Agriculture on Oct. 15 showed that they were infected with the virus, officials stated.

According to the statement, the outbreak prompted testing of workers at the farm, with samples tested at the Washington State Public Health Lab and sent to the Centers for Disease Control and Prevention (CDC), where they await final confirmation and analysis of the virus.

All four workers experienced mild symptoms and have been provided with antiviral medication, the department stated. Testing of other people on the farm is currently underway, and the number of cases under investigation may change in the coming days and weeks it noted.

Local health authorities are working with the CDC in response to the outbreak, and workers on the farm have been given personal protective equipment, according to the statement.

Other employees at the farm are also being monitored for symptoms, and testing, vaccines, and treatment are being provided to symptomatic workers.

The disease spreads easily among birds through nasal and eye secretions and through manure, and it can prove deadly in domestic poultry.

Bird flu symptoms in humans can range from mild to severe and can include conjunctivitis, mild flu-like upper respiratory symptoms, fatigue, shortness of breath, and difficulty breathing.