Fourth human bird flu case linked to US dairy cattle outbreak

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Colorado health officials have identified the state’s first human case of bird flu, linked to an ongoing outbreak in dairy cattle.


A fourth person in the United States has tested positive for H5 avian influenza, as part of an ongoing outbreak among dairy cattle across the country.

The Colorado Department of Public Health and Environment announced Wednesday that it has identified the state’s first human case of H5 avian influenza tied to the multistate outbreak of the virus in dairy cattle. The case is the fourth identified nationwide in connection with the outbreak; two other human cases have been reported in Michigan and one in Texas.

More than a quarter of Colorado’s dairy herds have reported cases of bird flu, according to data from the state health department. Through Wednesday, federal data shows that seven states have confirmed cases in the past 30 days, and 40% of those are in Colorado — more than any other state.

The infected person in Colorado had mild symptoms and reported only conjunctivitis or pink eye as a symptom, according to state health officials. He worked on a dairy farm in northeastern Colorado and had direct exposure to dairy cattle infected with bird flu.

After testing positive, the man was immediately treated with the antiviral drug oseltamivir and has recovered, the state health service said.

“The risk to most people remains low. Avian influenza viruses are currently spreading among animals, but they are not adapted to be spread from person to person. At this time, the most important thing to know is that people who regularly come into contact with infected animals are at increased risk of infection and should take precautions when in contact with sick animals,” Dr. Rachel Herlihy, state epidemiologist at CDPHE, said in Wednesday’s announcement. The last human case of H5N1 in Colorado was in 2022 in a person exposed to infected poultry.

In the current outbreak linked to infected dairy cattle, the first two human cases identified in the United States also reported eye-related symptoms and eye infections or conjunctivitis. The third human case in the US reported more respiratory symptoms, including coughing, congestion, sore throat and watery eyes. None of the three individuals had contact with each other, but all worked with cattle, suggesting that these are cases of cow-to-human transmission of the virus.

Nationally, the U.S. Centers for Disease Control and Prevention said it continues to closely monitor the situation, using its flu surveillance systems to watch for H5N1 activity in humans. The agency said Wednesday that the human case in Colorado “does not change CDC’s current H5N1 avian influenza risk assessment for the U.S. population, which the agency considers to be low.”

However, the case underscores “the importance of recommended precautions for people exposed to infected animals,” the CDC said. “People who have close or prolonged, unprotected exposure to infected birds or other animals (including livestock), or to environments contaminated by infected birds or other animals, are at greater risk of infection.”

The CDC has repeatedly recommended that dairy farmers wear personal protective equipment to reduce their risk. The U.S. Department of Agriculture has offered financial assistance to farms with infected animals to protect workers. Research continues into how infections are transmitted between cows and from cows to people who work with them.

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CDC officials said Tuesday that the United States has enough H5 bird flu tests to combat the outbreak.

“We have an ample supply of H5-specific tests in the public health system for the current outbreak. There are approximately 750,000 H5-specific tests available right now, and another 1.2 million such tests will come online in the next two to three months,” Dr. Nirav Shah, deputy director of the CDC, said at a news conference Tuesday.

“This is in addition to a robust supply of influenza A testing, the general testing that is available in doctor’s offices across the country,” Shah said. “The way our system works is that if someone tests positive for influenza A at the doctor’s office, their sample is sent to a public health lab for what’s called subtyping. That tells us whether the influenza A virus is a common seasonal virus, or a rarer version like H5N1. That subtyping is more common than you might think.”

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