CDC confirms first serious case of H5N1 bird flu in the United States

18 December 2024— 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 case of serious illness linked to the virus in the United States. The case was confirmed by the Centers for Disease Control and Prevention (CDC) on Friday, December 13. Since April 2024, a total of 61 human cases of H5 bird flu have been reported in the United States.

Partial viral genome data of the H5N1 avian influenza virus that infected the patient in Louisiana indicate 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 cases of people in British Columbia, Canada and Washington State. This H5N1 bird flu 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. Additional genomic sequencing and efforts to isolate virus from clinical samples 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 been exposed to sick and dead birds in backyard flocks. This is the first case of H5N1 bird flu in the United States linked to exposure to a backyard flock. A sporadic case of severe H5N1 avian influenza disease in a person is not unexpected; avian influenza A(H5N1) virus infection has previously been associated with severe human illness in other countries during 2024 and earlier years, including fatal illness. No person-to-person spread of H5 bird flu has been demonstrated. This case does not change CDC’s overall assessment of the immediate risk to public health from H5N1 avian influenza, which remains low.

This case highlights that in addition to affected commercial poultry and dairy operations, wild birds and backyard flocks may also be a source of exposure. People with occupational or recreational exposures to infected animals are at higher risk of infection and should follow the CDC’s recommended precautions when around animals infected or potentially infected with the H5N1 avian influenza virus. This means that owners of backyard herds, hunters and other bird enthusiasts should also take precautions.

The best way to prevent H5 bird flu is to avoid exposure whenever possible. Infected birds excrete avian influenza A virus in their saliva, mucus and feces. Other infected animals may shed avian influenza A virus in respiratory secretions and other body fluids (eg, in unpasteurized cow’s milk or “colostrum”).

• As a general precaution, people should, whenever possible, avoid contact with sick or dead animals, especially wild birds and poultry.
• For persons with direct/close contact with wild birds or sick or dead poultry or other animals, wear recommended personal protective equipment (PPE). Wild birds can become infected with avian influenza A virus even if they do not look sick.
• Do not touch surfaces or materials (eg animal waste or bedding) 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 bird flu in the United States and CDC’s response, including regularly updated case numbers, visit the H5 Bird Flu: Current Situation page.