A person in Louisiana who was hospitalized with a severe case of bird flu has died. The hospitalization, first announced Dec. 13, marked the first severe case of H5N1 bird flu in the United States. H5N1 is a subtype of bird flu that's been circulating among wild birds and poultry in the U.

The patient, who was older than 65 and had underlying medical conditions, was hospitalized weeks ago in critical condition with severe respiratory illness.