DENVER — A Colorado dairy worker has been diagnosed with bird flu, state health officials said Wednesday, becoming the fourth case tied to an unprecedented outbreak of highly pathogenic avian influenza among dairy cattle in the U.S.
Though this is the second confirmed infection of H5N1 in Colorado since the outbreak of HPAI H5N1 was first detected in March of 2022, Colorado health officials believe this is the first instance in which avian influenza was likely transmitted from a mammal to a human.
The dairy worker, who had direct exposure to dairy cattle infected with bird flu in northeast Colorado, had mild symptoms and reported only conjunctivitis, or pink eye, as his only symptom to state health officials. The dairy worker was tested for influenza at the State Public Health Laboratory and samples were then sent to the U.S. Centers for Disease Control and Prevention (CDC) for additional testing, which confirmed the infection, according to a spokesperson with the Colorado Department of Public Health and Environment (CDPHE).
The state provided the dairy worker antiviral treatment with oseltamivir in accordance with CDC guidance and has since recovered, the spokesperson said.
The CDPHE did not provide any information about when or how the man got infected, or whether testing had been expanded to other workers at the farm or to the man's family as a precaution.
“The risk to most people remains low. Avian flu viruses are currently spreading among animals, but they are not adapted to spread from person to person," said state epidemiologist Dr. Rachel Herlihy. "Right now, the most important thing to know is that people who have regular exposure to infected animals are at increased risk of infection and should take precautions when they have contact with sick animals."
The CDPHE is advising anyone who works with dairy cows that may have avian flu and who may start to feel sick, to call the state health department at 303-692-2700 (after normal business hours: 303-370-9395). Officials said the department can help those potentially exposed get a flu test and medicine if needed.
“We continue to work closely with the Colorado Department of Agriculture, local public health agencies, and CDC as we monitor this virus to protect all Coloradans,” said Scott Bookman, the senior director of public health readiness and response at the CDPHE in prepared remarks. “While it’s rare for people to become infected with avian flu viruses, direct exposure to infected animals increases that risk.”
So far, three other farm workers in the U.S. have contracted bird flu after coming into contact with sick cattle, according to the CDC, but none of the workers developed severe symptoms. Similar to the Colorado case, a Texas farm worker and the first of two Michigan cases developed pink eye from the infection. The third case — the second dairy farm worker in Michigan — developed more typical symptoms of acute respiratory illness, but all have since recovered.
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What’s my risk of catching bird flu?
Federal officials have stressed that the risk of catching bird flu for the general public is low, though risk depends on exposure, according to Herlihy, who said those in close contact with sick cattle or poultry are at greater risk of becoming infected with the virus.
So far, no human-to-human transmission of bird flu has been detected, according to the CDC.
The nation's top public health agency recommends that farm workers who come into contact with cattle suspected or confirmed to be infected with H5N1 wear disposable fluid-resistant coveralls, disposable gloves, boots or boot covers, vented safety goggles or a face shield, as well as an N95 respirator.
The general public should avoid contact with sick birds or other animals to reduce their chances of becoming infected with bird flu, Herlihy said. If you must handle sick or dead birds or animals, be sure to wear gloves, a high-quality mask such as a KN95 or N95 respirator, and eye protection. After handling the animal, double bag it and throw it away in your municipal trash can before thoroughly washing your hands with soap and warm water. If soap and water are not available, use an alcohol-based hand rub, the CDC recommends.
People should also avoid unprotected exposures to animal poop, bedding (litter), unpasteurized milk, or materials that have been touched by, or close to, birds or other animals with suspected or confirmed H5N1 infection, CDC officials said.
Can I catch bird flu from drinking milk or eating meat?
While early research lead by Federal Drug Administration (FDA) detected remnants of bird flu in retail milk, follow-up studies in which scientists tried to grow live virus from those grocery store samples did not yield any positive results.
Additional testing done by the FDA in mid-to-late April on nearly 300 dairy samples from 17 states also failed to detect any live, infectious virus, which they said reassured their previous statements that pasteurization is inactivating H5N1 in milk.
Other milk-related products that undergo pasteurization, such as cheeses, sour creams, yogurts, butters, etc., are also safe to eat, health officials said.
FDA officials have said the likelihood that eggs will contain H5N1 is low “due to the safeguards in place, which include testing of flocks and federal inspection programs,” that call for the disposal of eggs and meat from infected poultry. Proper egg storage and preparation “further reduce the risk,” they said.
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Though the agency “does not know at this time if the HPAI H5N1 virus can be transmitted to humans through consumption of raw milk and products made from raw milk from infected cows,” scientists are advising people to avoid raw milk and dairy products made from raw milk, as it does not go through the process of pasteurization, which inactivates harmful viruses and bacteria.
The warning came about a month after research showed a large number of cats who were fed raw milk in Texas suffered brain damage and later died, though scientists said they could not completely rule out if eating dead birds was how the cats came into contact with the virus in the first place.
In early June, the FDA sent a letter calling on state and tribal public health officials around the nation to curb the sale of raw milk and other raw milk products that may contain high levels of the virus.
Raw milk can't be sold in Colorado and a bill aimed at legalizing it for sale across the state died in the legislature this year, though Coloradans could still get it if they enter what's called a herd share agreement.
Though Colorado isn't testing swine and beef cattle for bird flu, ground beef appears to be safe for consumption after USDA researchers found no live virus in retail meat samples from states with ongoing outbreaks. The agency said it was confident that the meat supply was safe after at least three different safety studies found no viral particles in beef cattle, including one in which the meat was cooked to varying degrees of preparedness.
As of Monday, the Colorado Department of Agriculture had reported 27 of Colorado's 105 licensed dairies had been affected by outbreaks of H5N1 since the virus was first detected in the state in late April. More than 500 dairy workers were being monitored for possible exposure to bird flu as of this week, a CDPHE spokesperson said.
