CDC Confirms First-Ever Severe Case of H5N1 Bird Flu in the United States

The Centers for Disease Control and Prevention (CDC) has confirmed the first severe case of H5N1 avian influenza in Louisiana, United States. Health officials in the state reported that the patient, now hospitalized, likely contracted the virus through contact with backyard poultry. Health officials reported this case on December 13, identifying it as part of a global pattern of severe illness linked to poultry exposure. 

H5N1 D1.1 Genotype Identified in Louisiana Patient, CDC to Isolate Virus from Clinical Specimens

Viral genome analysis conducted of the H5N1 avian influenza virus from the patient indicates it belongs to the D1.1 genotype. This genotype has been recently identified in wild birds, poultry in the United States, and human cases in British Columbia, Canada, and Washington state. 

The B3.13 genotype differs and has been detected in dairy cows, sporadic human cases across multiple states, and some poultry outbreaks in the U.S. Reports indicate that the B3.13 genotype causes mild symptoms such as conjunctivitis. The CDC is conducting further genomic sequencing and attempting to isolate the virus from the patient’s clinical specimens.

First U.S. Case of H5N1 Linked to Backyard Poultry Exposure in 2024

CDC officials are investigating the source of the H5N1 infection in Louisiana and have determined that exposure to sick and dead birds in backyard flocks infected the patient. This marks the first U.S. case of H5N1 linked to backyard poultry exposure. Sporadic severe cases of H5N1 in humans have occurred in other countries during 2024 and previous years, sometimes resulting in death. No evidence of person-to-person transmission of H5N1 has been detected. The CDC states that the immediate risk to public health from H5N1 remains low.

Demetre Daskalakis, MD, MPH, director of CDC’s National Center for Immunization and Respiratory Diseases, said, “The demonstrated potential for this virus to cause severe illness in people continues to highlight the importance of the joint coordinated U.S. federal response, the One Health response, to address the current animal outbreaks in dairy cows and poultry and limit the potential transmission of this virus to humans through animal contact.”

The CDC has reported seven probable cases of H5N1 as of this year. The total number of lab-confirmed infections since the start of the year remains at 60, including two cases with unknown exposure. H5N1 continues to affect dairy cows in at least 16 states, with 860 herds impacted as of December 17. To help control the situation, the U.S. Department of Agriculture introduced a new federal order on December 6 requiring bulk testing of raw milk from dairy cows.

Health Officials Report 60 Confirmed H5N1 Cases and 7 Probable Cases So Far This Year

Since April 2024, reports have confirmed a total of 61 human cases of H5 bird flu nationwide. Along with the Louisiana case, Delaware recently reported a probable H5N1 infection identified through routine state influenza surveillance. The infected individual did not have known contact with sick animals. Despite multiple tests, the CDC could not confirm the type of influenza A virus, classifying the case as “probable.” This follows at least two previous cases with no known exposure.

“These two cases do not change CDC’s current risk assessment for the general population. The large number of animals—birds and mammals—infected with H5 bird flu increases the risk of the virus potentially infecting people and potentially adapting to cause human-to-human spread, reemphasized Dimitri Daskalakis. 

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Denisse Sandoval