Test tubes are seen labelled "Bird Flu" words in this illustration taken, June 10, 2024.

The U.S. Centers for Disease Control and Prevention said on Wednesday that a patient has been hospitalized with a severe case of H5N1 infection in Louisiana, marking the first known instance of a severe human illness linked to the bird flu virus in the United States.

The agency said it confirmed the case on Friday.

The CDC said that a sporadic case of severe H5N1 bird flu illness in a person is not unexpected as has previously been experienced in other countries during 2024 and prior years, including in cases that led to death. The agency said its assessment of risk to the public remains low.

CDC said that partial viral genome data from the infected patient shows that the virus belongs to the D1.1 genotype, recently detected in wild birds and poultry in the United States and in recent human cases in British Columbia, Canada, and Washington state.

This genotype of the virus is different from the B3.13 genotype detected in dairy cows, human cases in multiple states, and some poultry outbreaks in the country, CDC said.

There have been a total of 61 human cases of H5 bird flu reported in the United States since April, according to the CDC.

The Louisiana case is the first to be linked to backyard, non-commercial poultry, said Demetre Daskalakis, director of CDC's National Center for Immunization and Respiratory Diseases, on a call with reporters.

The virus has infected more than 860 dairy herds in 16 states since March and has killed 123 million poultry since the outbreak began in 2022.

There has not been evidence of dairy herds being reinfected once they have cleared the virus, said U.S. Department of Agriculture Deputy Under Secretary Eric Deeble on the press call.

The agency has enrolled 13 states in its newly launched national bulk milk bird flu testing plan, representing nearly half of the nation's milk supply, Deeble said.