A Louisiana man has become the first person in the United States to die of avian influenza, state health officials reported Monday. The patient, who was older than 65 and had underlying medical conditions, was hospitalized weeks ago in critical condition with severe respiratory illness related to the H5N1 bird flu virus. The patient, whom people familiar with the investigation have identified as a man, had been in contact with sick and dead birds in backyard flocks on his property, state health officials said in a statement.