Colorado health officials said they provided personal protective equipment to the facility where the man worked.
“We are still gathering additional information about worker exposure and PPE use,” state epidemiologist Rachel Herlihy said in a statement.
None of the farmworker’s household contacts have developed symptoms and there is no evidence of human-to-human transmission, Herlihy said. Local and state health officials are conducting follow-up investigations and will conduct additional testing if necessary, Herlihy said.
Two other dairy workers infected earlier — in Texas in April and Michigan in May — also reported eye inflammation. A second Michigan worker infected in late May reported coughing and eye discomfort with watery discharge. That worker was the first to report more widespread respiratory and eye symptoms.
Colorado health officials said the worker developed symptoms in late June, reported his symptoms a day later and was tested two days after his symptoms began. Those initial tests were inconclusive. Additional testing by the Centers for Disease Control and Prevention confirmed the presence of bird flu.
In 2022, a Colorado poultry worker tested positive for the same strain of bird flu. Worldwide, cases of human illness range from mild infections to more serious illnesses, including pneumonia.
Federal health and agriculture officials have repeatedly stressed the importance of dairy farm owners ensuring their employees take precautions — such as wearing personal protective equipment — when working with infected cattle. Federal and state authorities have made supplies available to dairy farms but have not required their use.
Dairy farm workers typically hand-pump milk from cows’ teats before attaching milking equipment. A splash of contaminated milk can get directly into the eyes, or the virus can enter when workers touch their eyes with a contaminated hand. Eye infections have been linked to previous human infections of avian influenza.
Many public health experts have said the lack of testing in cattle is hampering the ability to understand and control the outbreak, which was officially detected in March but may have been present in cows since December.
A recent Department of Agriculture study of H5N1 in 15 dairy herds and eight poultry flocks in Michigan found three risk factors for local spread, including contaminated equipment or machinery, people carrying the virus on their clothing or boots, and the animals themselves.
Federal health officials said this week that their risk assessment has not changed. The threat to the public remains low, and while dairy farm workers and others who come into contact with infected animals are at higher risk, U.S. officials are not recommending vaccination for any group of people.
Earlier this week, federal officials announced plans to expand vaccination and testing capacity in case the current outbreak of avian influenza in dairy cows leads to a surge in human cases, if the virus evolves to spread more easily or cause more severe illness, or if cases arise that are not linked to an infected herd or person.
The U.S. government has stockpiled 4.8 million doses of bird flu vaccine, and those doses are expected to be available starting in mid-July. The U.S. government has also granted $176 million to Moderna to complete development and testing of an mRNA-based vaccine against the H5N1 virus.
