A Michigan farmworker has been diagnosed with bird flu -- the second human case associated with an outbreak in U.S. dairy cows.
The patient had mild symptoms, Michigan health officials said in . The person had been in contact with cows presumed to be infected, and the risk to the public remains low, officials said.
In a statement, the CDC noted that an initial nasal swab turned up negative for influenza, but an eye swab sent to the agency tested positive for influenza A(H5) virus. Similar to the other U.S. case reported earlier this year, the Michigan patient only had eye symptoms.
The first case happened in late March, when a farmworker in Texas was diagnosed in what officials called the first known instance globally of a person catching this version of bird flu from a mammal. That patient reported eye inflammation and was treated with an antiviral drug.
"CDC has been watching influenza surveillance systems closely, particularly in affected states, and there has been no sign of unusual influenza activity in people, including in syndromic surveillance," the agency said, adding that the new Michigan case "does not change CDC's current H5N1 bird flu human health risk assessment for the U.S. general public, which the agency considers to be low."
Since 2020, a bird flu virus has been spreading among more animal species -- including dogs, cats, skunks, bears, and even seals and porpoises -- in scores of countries. The detection in U.S. livestock earlier this year was an unexpected twist that sparked questions about food safety and whether it would start spreading among humans.
That hasn't happened, although there's been a steady increase of reported infections in cows. As of Wednesday, the virus had been confirmed in 51 dairy herds in nine states, according to the U.S. Agriculture Department.
Fifteen of the herds were in Michigan. Health officials there have declined to say how many people exposed to infected cattle have been tested or monitored.
The new human case "underscores the importance of recommended precautions in people with exposure to infected or potentially infected animals," the CDC said.
The virus has been found in high levels in the raw milk of infected cows, but government officials say pasteurized products sold in grocery stores are safe because heat treatment has been confirmed to kill the virus.
The new case marks the third time a person in the U.S. has been diagnosed with what's known as Type A H5N1 virus. In 2022, a prison inmate in a work program picked it up while killing infected birds at a poultry farm in Montrose County, Colorado. His only symptom was fatigue, and he recovered. That predated the virus's appearance in cows.