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.

The bird flu virus that brought a Canadian teen to the “brink of death” may have mutated while inside her body to become more efficient at spreading among humans. The case, and the death of a Louisiana resident over the age of 65 who was hospitalized with a severe H5N1 avian flu infection in December,