A ny time a person catches H5N1, or bird flu, their infection is a chance for the virus to mutate in the wrong direction. When someone dies from the bird flu—as an elderly Louisiana man did on Jan. 6, becoming the first U.S. death from the disease—experts get especially concerned.

On Monday, Louisiana health officials announced that a person hospitalized last month with a severe case of avian influenza — also known as H5N1 bird flu — died. This is the first human death from bird flu in the U.S.