By Wes Stubblefield, MD, MPH, FAAP
ADPH Medical Officer

H5N1 influenza, or “bird flu,” is a type of influenza that was first discovered in the 1950s. In 1996, a variant of H5N1 was documented overseas that resulted in a severe illness in birds and was designated as highly pathogenic avian influenza (HPAI). Since 2016, HPAI H5N1 has been detected in wild birds in the United States during screening efforts by wildlife authorities. 

H5N1 is currently known to be widespread among wild birds and is thought to be spread by migratory waterfowl. Occasionally, this may result in infections in domestic poultry resulting in large-scale culling operations or even localized infections in backyard flocks. To date, more than 160 million poultry are known to have been affected.

Since the 1990s, this type of influenza virus has been associated with sporadic crossover infections from birds to humans. Prior to the current U.S. cases in 2024-2025, H5N1 disease in humans had a high mortality rate of up to 50%. However, the 68 human cases in the U.S. since 2024, have primarily been very mild with symptoms consisting of conjunctivitis and upper respiratory symptoms with or without fever. There have been a few severe cases and one individual died with H5N1 infection. It is important to note that no human-to-human transmission has been documented in any of the cases.

Although the virus has been known to spread from birds to humans, current recent HPAI strains have caused widespread infections in domestic cattle and specifically among dairy cattle. This influenza infection primarily presents in cattle as decreased milk production, lethargy, and decreased appetite. Testing has found that high concentrations of the virus are found in the udder and milk and spread among cattle and from cattle to humans are likely due to milking operations. Numerous other mammal species are also known to have been infected such as cats and raccoons. 

Historically, only H1 and H3 types of influenza have resulted in epidemic or pandemic influenza and the current risk of H5N1 to humans is still considered to be low by CDC. For the infection to become highly contagious to and among people, considerable mutations to the virus’ binding sites would have to occur. Most of the documented infections have been associated with direct contact to infected birds or cattle with extremely high viral inoculations.

The Alabama Department of Public Health and the Alabama Department of Agriculture and Industries, along with the Centers for Disease Control and Prevention, the United States Food and Drug Administration, and the United States Department of Agriculture are monitoring this situation very closely and hold regular meetings on the subject. The CDC regularly sequences isolates for changes that may lead to antiviral resistance and/or increased infectivity. Also, CDC has provided a candidate vaccine virus to manufacturers for rapid production if needed.

For providers, it is highly encouraged to submit samples from hospitalized patients to a laboratory capable of identifying H5N1 if influenza is confirmed in the inpatient setting and H5N1 is suspected. These samples might include samples that are only identified as influenza “A” and as “non-H1/non-H3” on an enhanced assay. In the outpatient setting, this might include those with exposure-related risk factors and confirmed influenza. Several commercial laboratories are providing this service including Quest, LabCorp, ARUP and Mayo. The Bureau of Clinical Laboratories at ADPH is also providing testing but should be prioritized for patients that are underinsured or uninsured.

For the public, cautious monitoring is recommended. This might include watching backyard poultry for symptoms or reporting sick or dead birds. Sick or dead wild birds should be reported to the Alabama Department of Natural Resources and Conservation at 334-242-3469 and sick or dead domestic birds should be reported to the Agriculture Department’s Poultry Unit at 334-240-6584. Sick or dead birds should not be handled. Also, as raw milk is known to contain active H5N1 virus which is not found in pasteurized products, the consumption of raw milk is highly discouraged.

Finally, visit the website below for the latest information regarding isolation, treatment, and prophylaxis for those known or suspected to be infected or exposed to H5N1. This information has and is subject to change based on this evolving situation.

https://www.cdc.gov/bird-flu/situation-summary/index.html

https://www.alabamapublichealth.gov/flu/flua-acceleratedsubtyping-hospitals.pdf