Three poultry workers tested positive for bird flu and more who showed symptoms of infection are being tested, state health officials announced Friday evening.
The outbreak of human cases, if confirmed, is the largest in the United States from the strain of bird flu — also known as highly pathogenic avian influenza — currently circulating across the globe.
The workers who tested positive were responding to an outbreak of bird flu at a commercial egg-laying operation in Weld County, where nearly 1.8 million chickens were being culled following the virus’s discovery. None of the workers required hospitalization. Their symptoms ranged from pink eye to what the state described in a news release as “common respiratory infection symptoms.”
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Samples taken from the workers tested positive at the state lab. They have now been sent to the federal Centers for Disease Control and Prevention for official confirmation.
The Colorado Department of Public Health and Environment wrote in a news release that “additional samples from symptomatic workers” will be tested over the weekend.
Before Friday, there had been only five known human cases of bird flu in the United States since 2022. One of those, the first discovered in the country from the current strain, was in a worker at a poultry farm in Montrose County in 2022. Another was identified last week in a dairy worker in Weld County. There have also been three other infections discovered in dairy workers in Texas and Michigan.
So far, every person infected in the United States has experienced mild symptoms and recovered with the help of antiviral medication.
Colorado has emerged as the epicenter of the bird flu epidemic in the United States. In addition to its at least five human cases, Colorado now has the nation’s worst outbreak of bird flu among dairy cattle.
State agriculture officials identified eight new infected dairy herds this week, bringing the state’s total number of cases in dairy cattle to 35 since April. That places Colorado first among states, seven cases ahead of Idaho, which like most other states with large numbers of outbreaks has a far larger dairy industry than Colorado. About a third of Colorado’s dairy herds have now been infected.
Bird flu, as the name indicates, typically circulates in birds, and it can be particularly devastating if it infects domestic poultry. But the current strain circulating the globe has distinguished itself by its ability to infect a wide variety of animals. Bears, mountain lions, seals, skunks, cats and more have all died from bird flu in recent years.
Humans have occasionally been infected by bird flu in the past — with some strains carrying a high fatality rate — but there has never been sustained person-to-person transmission of the virus. Instead, infections tend to occur following close contact with infected animals, which is what state health officials speculate occurred for the newest human outbreak in Weld County.
There has been no documented instance in the U.S. of person-to-person transmission from the current bird flu strain, and health officials believe the risk to the general public remains low.
“Where we need to ramp up the level of concern in the population is when we see those … workers get infected and spread it to their families,” Elizabeth Carlton, an epidemiologist at the Colorado School of Public Health, told The Colorado Sun earlier this month.
Eating poultry, eggs or beef remains safe, so long as they are cooked to the appropriate temperature. Drinking milk is also safe, so long as it is pasteurized.
People who work with cows or poultry should be especially vigilant about hand-washing and other good-hygiene practices. If they start to feel sick, they should seek medical attention or call CDPHE at 303-692-2700 or 303-370-9395 after normal business hours.