The Colorado Department of Public Health and Environment on Thursday announced three additional human cases of bird flu among poultry farm workers, bringing the total number of confirmed human cases in the US this year to 13, reported Reuters. 

The three new cases involved poultry farm workers who were killing infected chickens at a Weld County egg farm, the health department said. The workers are experiencing mild illness and have been offered antiviral drugs, said the US Centers for Disease Control and Prevention (CDC) in a statement.

Neither the state health department nor CDC provided the name of the egg farm.

The bird flu outbreak has infected poultry in nearly every US state since early 2022. Since March, the virus has been circulating among dairy cattle and has infected more than 170 herds in 13 states, according to the US Department of Agriculture.

Since April, four dairy farm workers and nine poultry farm workers have been infected with the virus in Colorado, Michigan and Texas.

The CDC said the risk to the general public from bird flu remains low, but that farm workers exposed to infected animals should use personal protective equipment (PPE).

Six workers culling infected chickens at a different Colorado chicken farm earlier this month were working without effective PPE, according to the CDC.

A CDC field team is deployed in Colorado to support its ongoing outbreak response, the agency said.