A man in Colorado has tested positive for an H5 bird flu virus, state official and the Centers for Disease Control and Prevention said on Thursday, marking the first recorded human infection in the US of the highly contagious virus that is ripping through commercial flocks and wild birds, but that experts say poses little threat to humans.

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The Colorado Department of Public Health and Environment (CDPHE) said the man is incarcerated at a state correctional facility and was exposed to infected poultry while working at a commercial farm in Montrose County.

The man tested positive for an avian influenza A(H5) virus earlier this week and the CDC confirmed the result on Wednesday, the CDPHE said, though repeat testing was negative for influenza.

It’s possible the person may not have actually been infected with the virus, the CDPHE noted, suggesting the virus may have been present in his nose due to close contact with infected poultry but did not cause an infection.

The man—described as younger than 40, “largely asymptomatic” and reporting only fatigue—is now isolating and taking the antiviral drug oseltamivir, also known as tamiflu, the CDPHE said.

No other cases have been confirmed in humans in Colorado or the US, the CDPHE said.