On Dec. 18, 2024, the U.S. Centers for Disease Control and Prevention (CDC) reported that a patient has been hospitalized with a severe case of avian influenza A(H5N1) virus (“H5N1 bird flu”) infection in Louisiana. This marks the first instance of severe illness linked to the virus in the United States. The case was confirmed by the Centers for Disease Control and Prevention (CDC) on December 13.

Since April 2024, there have been a total of 61 reported human cases of H5 bird flu reported in the United States. Partial viral genome data of the H5N1 avian influenza virus that infected the patient in Louisiana indicates that the virus belongs to the D1.1 genotype related to other D1.1 viruses recently detected in wild birds and poultry in the United States and in recent human cases in British Columbia, Canada, and Washington state. This H5N1 bird flu genotype is different than the B3.13 genotype detected in dairy cows, sporadic human cases in multiple states, and some poultry outbreaks in the United States. Additional genomic sequencing and efforts to isolate virus from clinical specimens from the patient in Louisiana are underway at CDC.

While an investigation into the source of the infection in Louisiana is ongoing, it has been determined that the patient had exposure to sick and dead birds in backyard flocks. People with work or recreational exposures to infected animals are at higher risk of infection and should follow CDC’s recommended precautions when around animals that are infected or potentially infected with H5N1 avian influenza virus.