A dairy in Weld County has tested positive for highly pathogenic avian influenza, marking Colorado's first case of bird flu in dairy cattle since August 2024. The dairy, which state officials have not named, is now under quarantine, with milk cows barred from leaving the property and strict biosecurity protocols required across the farm.
The case came to light after a routine bulk milk tank test returned a presumptive positive result, according to The Denver Post. The U.S. Department of Agriculture's lab confirmed highly pathogenic avian influenza in the milk on October 24, while testing performed at Colorado State University's veterinary lab first detected the virus, with the finding later confirmed by the National Veterinary Services Laboratory, according to The Colorado Sun.
Quarantine Rules and Weekly Testing
The quarantine order requires the dairy to undergo weekly bulk milk tank testing until it produces two consecutive negative results at least a week apart, the Sun reported. Colorado's agriculture department had described the initial test result as presumptive positive for HPAI, according to a news release from the Colorado Department of Agriculture. State agriculture officials said they are working closely with the Colorado Department of Public Health and Environment and local agencies, and are working to protect workers at the dairy.
Colorado Agriculture officials said the detection reinforces why the state's testing program matters in the first place. “This detection underscores the importance of our routine bulk milk tank testing to keep our herds healthy and our food supply secure,” the department said, per the Sun's reporting.
Why Officials Say Milk Remains Safe
State health officials maintain that the risk to the general public remains low and that pasteurization kills the virus before milk reaches store shelves. “When milk is pasteurized, the process would kill the virus,” officials said, according to the same account. People face the greatest risk of infection through direct contact with infected birds or animals, not through drinking pasteurized milk, officials added.
This is not Colorado's first brush with the virus in dairy herds. An outbreak that began in April 2024 eventually spread to 64 dairies statewide, prompting Colorado to become the first state in the nation to institute mandatory bulk milk tank testing for commercial dairies that year. That testing program ultimately cleared the virus from all affected herds, and every dairy in the state had been released from quarantine by December 2024, state officials said.
A National Pattern of Renewed Spread
Colorado isn't alone in confronting a fresh round of the virus this fall. Avian flu has spread to 27 dairy farms in Washington state within the past three weeks, the Sun reported. In Washington, a dairy affected by the virus has employed strict biosecurity measures while veterinarians work to treat sick cows, according to a release from the Washington State Department of Agriculture. That release also noted that pasteurized milk products remain safe for consumers and that milk supply shortages are not expected.
For now, the Weld County dairy remains under quarantine as weekly testing continues. State officials have not released the dairy's name or additional details about the scope of the infection within the herd.
