H5 Bird Flu: Latest Updates on Outbreaks and Human Cases

The H5 bird flu, also known as avian influenza A (H5N1), continues to spread globally, impacting wild birds, poultry, and, increasingly, mammals including dairy cows. Although the overall public health risk remains low, health officials are closely monitoring the situation, particularly as sporadic human cases emerge.

Current Situation in the United States

As of February 24, 2026, the Centers for Disease Control and Prevention (CDC) has confirmed 18 human cases of H5 bird flu in the United States since 2022, with 17 cases occurring in 2024 . Recently, a third human case was identified in California, linked to occupational exposure to infected dairy cows. Like the two previous cases in California, the individual experienced mild symptoms, specifically eye redness or discharge (conjunctivitis), and did not require hospitalization .

These three California cases, occurring on separate farms and among workers with no known contact, strongly suggest animal-to-human transmission. The CDC is currently awaiting confirmatory testing on two additional presumptive positive specimens from California .

Viral Characteristics and Monitoring

Sequencing of the first two California cases revealed the presence of clade 2.3.4.4b A(H5N1) viruses, closely related to those detected in dairy cattle. Whole genome sequencing of one case (A/California/135/2024) identified a B3.13 genotype virus. Importantly, no genetic changes were observed that would suggest increased transmissibility between humans or reduced susceptibility to antiviral medications . Sequencing is underway for the third confirmed case.

The CDC is actively monitoring the situation through its influenza surveillance systems, with data on human monitoring and testing available monthly . Data on highly pathogenic avian influenza (HPAI) detections in animals can be found on the U.S. Department of Agriculture (USDA) website.

Understanding Bird Flu

Bird flu, or avian influenza, is caused by a virus that can cause severe illness and even death in birds and mammals . Human infections are rare, but can occur through contact with infected birds or animals, or through inhalation of the virus .

Risk and Prevention

The CDC continues to emphasize the importance of precautions for individuals with exposure to infected or potentially infected animals. People with close or prolonged, unprotected contact with infected birds, other animals (including livestock), or contaminated environments are at higher risk of infection .

As of December 2024, Los Angeles County reported one human case of H5 bird flu .

Key Takeaways

• H5 bird flu is widespread in wild birds and poultry, with increasing cases in mammals.
• Human cases are rare and typically mild, but are being closely monitored.
• The current public health risk remains low.
• Precautions should be taken by those with exposure to infected animals.