Summary
The Centers for Disease Control and Prevention (CDC) is issuing this Health Alert Network (HAN) Health Advisory to inform clinicians, state health departments, and the public of a recently confirmed human infection with highly pathogenic avian influenza (HPAI) A(H5N1) virus in the United States following exposure to presumably infected dairy cattle. The U.S. Department of Agriculture (USDA) recently reported detections of highly pathogenic avian influenza A(H5N1) virus in U.S. dairy cattle in multiple states. This Health Advisory also includes a summary of interim CDC recommendations for preventing, monitoring, and conducting public health investigations of potential human infections with HPAI A(H5N1) virus.

Background
A farm worker on a commercial dairy farm in Texas developed conjunctivitis on approximately March 27, 2024, and subsequently tested positive for HPAI A(H5N1) virus infection. HPAI A(H5N1) viruses have been reported in the area’s dairy cattle and wild birds. There have been no previous reports of the spread of HPAI viruses from cows to humans.

The patient reported conjunctivitis with no other symptoms, was not hospitalized, and is recovering. The patient was recommended to isolate and received antiviral treatment with oseltamivir. Illness has not been identified in the patient’s household members, who received oseltamivir for post-exposure prophylaxis per CDC Recommendations for Influenza Antiviral Treatment and Chemoprophylaxis. No additional cases of human infection with HPAI A(H5N1) virus associated with the current infections in dairy cattle and birds in the United States, and no human-to-human transmission of HPAI A(H5N1) virus have been identified.

CDC has sequenced the influenza virus genome identified in a specimen collected from the patient and compared it with HPAI A(H5N1) sequences from cattle, wild birds, and poultry. While minor changes were identified in the virus sequence from the patient specimen compared to the viral sequences from cattle, both cattle and human sequences lack changes that would make them better adapted to infect mammals. In addition, there were no markers known to be associated with influenza antiviral drug resistance found in the virus sequences from the patient’s specimen, and the virus is closely related to two existing HPAI A(H5N1) candidate vaccine viruses that are already available to manufacturers, and which could be used to make vaccine if needed.

This patient is the second person to test positive for HPAI A(H5N1) virus in the United States. The first case was reported in April 2022 in Colorado in a person who had contact with poultry that was presumed to be infected with HPAI A(H5N1) virus.

Currently, HPAI A(H5N1) viruses are circulating among wild birds in the United States, with associated outbreaks among poultry and backyard flocks and sporadic infections in mammals.

The current risk these viruses pose to the public remains low. However, people with job-related or recreational exposures to infected birds, cattle, or other animals are at higher risk of infection and should take appropriate precautions outlined in CDC Recommendations for Farmers; Poultry, Backyard Bird Flock, and Livestock Owners; and Worker Protection.

CDC continues to work with USDA, FDA, and state health departments to monitor people exposed to animals infected with HPAI A(H5N1) viruses. The FDA does not currently have concerns about the safety or availability of pasteurized milk products nationwide. Pasteurization has continually proven to inactivate bacteria and viruses, like influenza viruses, in milk and is required for any milk entering interstate commerce. Because influenza viruses constantly change, continued surveillance and preparedness efforts are critical. CDC is taking measures in case the public health risk assessment changes. This is a developing situation, and CDC will share additional updates as new relevant information becomes available.

No case of severe illness or death with HPAI A(H5N1) virus infection has been reported in the United States. Since 1997, more than 900 sporadic human cases of HPAI A(H5N1) have been reported in 23 countries, with more than half of these cases resulting in death. However, since 2015–2016, human cases have decreased substantially, and only a small number of sporadic human cases have been reported worldwide since 2022. Clinical illness with HPAI A(H5N1) virus infection has ranged from mild disease (e.g., conjunctivitis and upper respiratory symptoms) to severe or critical disease (e.g., pneumonia, multi-organ failure, and sepsis) and death.

Recommendations
CDC’s updated recommendations include instructions for infection prevention and control measures, using personal protective equipment (PPE), testing, antiviral treatment, patient investigations, monitoring of exposed persons (including persons exposed to sick or dead wild and domesticated animals and livestock with suspected or confirmed infection with HPAI A(H5N1) viruses), and antiviral chemoprophylaxis of exposed persons.