A Colorado man has tested positive for an H5 bird flu virus, the first such case in the U.S., health officials said April 28.
The Colorado health department said the man, who is younger than 40, had been working on a commercial farm with poultry that, according to the CDC, was presumably infected with H5N1. He reported fatigue as his only symptom and is now in isolation and being treated with the flu antiviral drug oseltamivir.
It's unclear whether the exposure resulted in an infection, according to statements from the health agencies. Officials from the Colorado health department said a positive test result came from a single nasal specimen. The CDC confirmed that result April 27, though it said repeat testing has been negative.
"Because the person was in close contact with infected poultry, the virus may have been present in the person's nose without causing infection," the Colorado health department said. The CDC said whether the positive test was the result of "surface contamination of the nasal membrane" cannot be determined now.
"The appropriate public health response at this time is to assume this is an infection and take actions to contain and treat," the CDC said, adding risk to the general public remains low.
The CDC has been monitoring H5N1 outbreaks among wild birds and poultry since late 2021. The agency said it has been tracking the health of more than 2,500 people with exposure to infected birds, and this marks the only detected case. The first such human infection caused by the predominant group of H5N1 viruses now circulating was reported in the U.K. in December.