December 18, 2024– A patient was hospitalized in Louisiana with a severe case of avian influenza A(H5N1) virus infection (“H5N1 Avian Influenza”). This is the first case of serious illness related to the virus in the United States. The case was confirmed by the Centers for Disease Control and Prevention (CDC) on Friday, December 13th. Since April 2024, a total of 61 human cases of H5 avian influenza have been reported in the United States.

Partial viral genomic data from the H5N1 avian influenza virus that infected the Louisiana patient suggests that the virus belongs to the D1.1 genotype and is related to other D1.1 viruses recently identified in wild birds and poultry in the United States States and recent human cases have been discovered in British Columbia, Canada and Washington state. This H5N1 avian influenza genotype is different from the B3.13 genotype that has been detected in dairy cows, sporadic human cases in several states, and some poultry outbreaks in the United States. Further genomic sequencing and efforts to isolate the virus from clinical samples from the Louisiana patient are underway at the CDC.

While an investigation into the source of the infection is ongoing in Louisiana, it was determined that the patient had contact with sick and dead birds in backyard flocks. This is the first case of H5N1 avian influenza in the United States that has been linked to exposure to a backyard flock. A sporadic case of severe H5N1 avian influenza illness in an individual is not unexpected; Infection with the avian influenza virus A(H5N1) has been linked to severe human illness, including fatal illness, in other countries as early as 2024 and in previous years. No human-to-human transmission of H5 avian influenza has been detected. This case does not change the CDC’s overall assessment of the immediate public health risk of H5N1 avian influenza, which remains low.

This case highlights that in addition to affected commercial poultry and dairy operations, wild birds and backyard flocks can also be a source of exposure. People who are occupationally or recreationally exposed to infected animals are at higher risk of infection and should follow CDC-recommended precautions when around animals infected or potentially infected with the H5N1 avian influenza virus. This means that backyard herd owners, hunters and other bird lovers should also take precautions.

The best way to prevent H5 bird flu is to avoid exposure if possible. Infected birds excrete avian influenza A viruses through their saliva, mucous membranes and feces. Other infected animals can shed avian influenza A viruses through respiratory secretions and other body fluids (e.g. in unpasteurized cow’s milk or “raw milk”).

• As a general precaution, people should avoid contact with sick or dead animals, especially wild birds and poultry, whenever possible.
• Wear recommended personal protective equipment (PPE) when in direct/close contact with wild birds, sick or dead poultry, or other animals. Wild birds can become infected with avian influenza A viruses even if they do not appear sick.
• Do not touch surfaces or materials (e.g., animal bedding or bedding material) that are contaminated with saliva, mucus, or animal feces from wild or domestic birds or other animals with confirmed or suspected avian influenza A virus infection.

For more information about H5 Avian Influenza in the United States and the CDC’s response, including regularly updated case numbers, visit the H5 Avian Influenza Current Situation page.