A person in Louisiana has the first severe illness caused by bird flu in the U.S., health officials said Wednesday.

The patient had been in contact with sick and dead birds in backyard flocks, the U.S. Centers for Disease Control and Prevention (CDC) said. Agency officials didn’t immediately detail the person’s symptoms.

Previous illnesses in the U.S. had been mild and the vast majority had been among farm workers exposed to sick poultry or dairy cows.