Fourth bird flu case in US in 2024 appears in Colorado, CDC says

A fourth person has been infected with bird flu this year as an outbreak among dairy cows continues across the U.S., federal health officials announced Wednesday. The four people who contracted the virus live in three states.

The case of a Colorado dairy worker is the state's first this year. Health officials identified the first U.S. case of avian influenza in 2022, in an incarcerated person who was exposed to infected chickens at a Colorado poultry farm. The first case in the 2024 outbreak was identified in Texas, and two cases in Michigan followed, according to the Centers for Disease Control and Prevention.

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Colorado health officials said the man, who worked on a dairy farm in northeast Colorado, had direct contact with cattle infected with avian influenza. He was being monitored because of his work exposure to H5N1 virus-infected cows. He did not have contact with the three people infected earlier this year in Texas and Michigan.

The Colorado man developed symptoms in late June, said Sasha Geffen, a spokesperson for the state Department of Public Health and Environment, in an email. The next day, the man reported his illness to state health officials, who found he had mild symptoms of conjunctivitis, or pinkeye, a condition present in other workers who became sick this year.

He was tested two days after symptoms began, but results of his infection by state laboratories were inconclusive, Geffen said. After officials sent specimens to the CDC for testing, the CDC learned on Tuesday the man tested positive for avian influenza. He received oseltmavir, an antiviral drug, and has recovered, CDC said.

Colorado officials maintain the current public health risk remains low. The CDC also said the Colorado case doesn’t change the federal health agency’s assessment that the overall risk to the general public is low. The subtype of the bird flu virus the Colorado man has will be determined after genetic sequencing, CDC officials said. That information could be released in the next couple of days and help officials identify changes to the virus and calculate the risk.

“Avian flu viruses are currently spreading among animals, but they are not adapted to spread from person to person,” Dr. Rachel Herlihy, state epidemiologist for Colorado's public health department, said in a statement. “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 people who tested positive for bird flu this year were all dairy workers at farms where cows had tested positive for bird flu, the CDC said. Officials said this underscores that it is crucial to take precautions if you have extensive exposure to infected animals. Working in these circumstances poses a greater risk of infection.

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Over 130 U.S. dairy herds have been found to have infected cattle in 12 states. Bird flu is common among wild birds, and officials believe the virus spilled over from wild birds to cows. The infected cows then transmitted it to four people in close contact with the animals.

There have been no human-to-human transmissions during this outbreak. Such a finding would stoke alarm among public health officials.

Earlier this week, federal officials announced plans to ramp up vaccine production for bird flu vaccines in case more humans become infected.

This article originally appeared on USA TODAY: Bird flu hits Colorado in fourth case in 2024, CDC says