The Louisiana patient who contracted what officials said was the nation’s first “severe” case of avian influenza has died, the state health department said Monday. The person who contracted the H5N1 strain of highly pathogenic bird flu in southwest Louisiana had been hospitalized since mid-December.

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

A person in Louisiana who contracted a severe case of avian influenza last month died Monday, marking the first case of a death in the U.S. following contraction of the virus.