Colorado reports 5 human cases of H5N1 bird flu

Five poultry workers have been infected with H5N1 bird flu while working at a farm in northeast Colorado, an unusual cluster of human cases though only mild symptoms have been reported, according to state and federal officials.

The Colorado Department of Public Health reported the first three cases on Friday and confirmed two more on Sunday night. All of them were involved with the culling of poultry at a commercial egg laying operation where animals were infected with H5N1.

Those infected reported mild symptoms, including conjunctivitis (pink eye) and common respiratory infection symptoms, which may include fever, chills, coughing, sore throat and a runny nose. None of them were hospitalized.

“These preliminary results again underscore the risk of exposure to infected animals,” the CDC said in a statement on Friday. “There are no signs of unexpected increases in flu activity otherwise in Colorado, or in other states affected by H5 bird flu outbreaks in cows and poultry.”

LINK: A list of all human cases of H5N1 bird flu since 2021

The global spread of H5N1 clade 2.3.4.4b – and the recent spread to a growing number of mammals – has raised concern about the possibility of human-to-human transmission from a future variant, though so far only a few human cases have been found after contact with infected birds or cattle.

Nineteen human cases of H5N1 bird flu have been reported so far this year, including 9 in the U.S., 7 in Cambodia and one each in Australia, Vietnam and China. Only the U.S. cases – 6 in Colorado, 2 in Michigan and 1 in Texas – were caused by the newer variant, clade 2.3.4.4b. None of the U.S. cases were fatal.

Human bird flu cases in the U.S.