Fourth Case of Avian Influenza Confirmed in US


The case occurred to a man in Colorado who had direct contact with cattle and state public health officials offer details on the patient as well as the risk to the public.

cattle together; Image credit: Annie Spratt, Unsplash

A fourth case was confirmed yesterday in a person who had direct contact with cattle.
Image credit: Annie Spratt, Unsplash

The fourth case of avian influenza in the United States was confirmed in Colorado yesterday. This case was in an employee at a dairy farm in the northeast part of the state and who had direct exposure to dairy cattle infected with avian flu. Specifically, the Colorado Department of Public Health and Environment, working in coordination with the Centers for Disease Control (CDC) and Prevention and Colorado Department of Agriculture, identified an adult man having a confirmed case. The man had mild symptoms, reporting only conjunctivitis (pink eye).1

He reported his symptoms to state health officials, who tested him for influenza at the State Public Health Laboratory. Specimens forwarded to CDC for additional testing were positive for avian flu.1

CDPHE gave the patient antiviral treatment with oseltamivir in accordance with CDC guidance. He has recovered.1

Another singular case of avian influenza was confirmed in Colorado back in 2022, and that patient recovered as well.1

Learn More: Deconstructing the Avian Flu

What You Need to Know

The latest avian influenza case is the fourth in the US, and it involves a Colorado farmworker exposed to infected dairy cattle. The Colorado Department of Public Health and Environment (CDPHE) confirmed this case in coordination with the CDC and state agriculture department.

Avian influenza is currently zoonotic in transmission, from animals to humans, in close contact with infected animals.

The CDC advises the public to avoid unprotected contact with sick or dead animals, raw milk, and uncooked animal products from potentially infected sources.

“Our partnership with the Colorado Department of Agriculture has been crucial in disseminating information to dairy farmers across the state,” said Jill Hunsaker Ryan, executive director, CDPHE. “Coloradans should feel confident that the state is doing everything possible to mitigate the virus.”1

What We Know So Far

In 3 of the 4 confirmed cases in the US, the patients have had conjunctivitis as the main presenting symptom. All patients have recovered and all were working with cows in traditional farm settings.

Right now, transmissibility is strictly zoonotic, so it is just occurring between cattle and people.

“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. 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,” said Rachel Herlihy, MD, MPH, state epidemiologist, CDPHE.1

Nonetheless, there are general public health concerns if transmissibility between humans should occur.

“When we think about this from a virus perspective, there does seem to be 2 different barriers to this virus, getting into humans—that’s first,” Richard Webby, PhD, director of the World Health Organization Collaborating Centre for Studies on the Ecology of Influenza in Animals and Birds and Department of Host-Microbe Interactions, Division of Virology, St. Jude Children's Research Hospital said in a recent interview with Contagion. “So, bird to human is a little bit lower [transmission] than that second, which is the human-to-human transmission. But now, that's why we get a little bit worried when we see mammals infected with this virus…In that environment, that's where we think the virus is going to get the most chances to make the changes it needs to successfully go human to human.”2

And when the jump goes from zoonotic then to human-to-human transmission there are mutations involved in the virus possibly making it more transmissible and vulnerable to a pandemic scenario, says Webby.2

Avian Influenza Prevention

For now, there are precautions people can perform. According to CDC, the general public should avoid unprotected exposure to sick or dead animals including wild birds, poultry, other domesticated birds, and other wild or domesticated animals (including cattle), as well as with animal carcasses, raw milk, feces, litter, or materials contaminated by birds or other animals with confirmed or suspected avian influenza infection.2

Additionally, people should not prepare or eat uncooked or undercooked food or related uncooked food products, such as unpasteurized (raw) milk, or products made from raw milk such as cheeses, from animals with confirmed or suspected HPAI A(H5N1)-virus infection.2


1.Colorado state health officials identify a human case of avian flu. CDPHE press statement. July 3, 2024. Accessed July 4, 2024.
2. Parkinson J. Deconstructing the Avian Flu. Contagion. April 9, 2024. Accessed July 4, 2024.
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