A person in the United States has tested positive for the highly pathogenic avian influenza (HPAI) A(H5N1) virus, commonly known as H5N1 bird flu, according to reports from Texas and confirmation by the CDC. This individual was exposed to dairy cattle in Texas, and presumed to be infected with HPAI A(H5N1) viruses. The patient exhibited eye redness, consistent with conjunctivitis, as their only symptom and is currently recovering. The patient has been advised to isolate and is receiving treatment with an antiviral drug for flu.
Despite this infection, the H5N1 bird flu human health risk assessment for the general public in the U.S. remains low, as evaluated by the CDC. Nonetheless, individuals with close or prolonged, unprotected exposures to infected birds or animals (including livestock), or environments contaminated by such animals, are at a higher risk of infection. The CDC has issued interim recommendations for prevention, monitoring, and public health investigations of HPAI A(H5N1) viruses.
The CDC, in collaboration with state health departments, continues to monitor workers who may have been in contact with infected or potentially infected animals and is testing those who develop symptoms. Additionally, the CDC provides recommendations for clinicians regarding the monitoring, testing, and antiviral treatment of patients with suspected or confirmed avian influenza A virus infections.
This case marks the second person in the United States reported to have tested positive for influenza A(H5N1) viruses. The first case occurred in Colorado in 2022. Although human infections with avian influenza A viruses, including A(H5N1) viruses, are rare, they have occurred sporadically worldwide. The CDC has been vigilant in monitoring illness among individuals exposed to H5 virus-infected birds since outbreaks were first detected in U.S. wild birds and poultry in late 2021. Human illnesses caused by the H5N1 bird flu have varied from mild conditions, such as eye infections and upper respiratory symptoms, to severe illnesses, like pneumonia, which have resulted in fatalities in other countries.
H5 bird flu is widespread among wild birds in the U.S. and globally. These viruses have also led to outbreaks in commercial and backyard poultry flocks and sporadic infections in mammals. The presence of HPAI in dairy cattle was first identified in Texas and Kansas by the U.S. Department of Agriculture (USDA) on March 25, 2024. Unpasteurized milk from affected cattle collected from two dairy farms in Kansas and one in Texas, as well as a throat swab from a cow in another dairy in Texas, tested positive for HPAI A(H5) viruses of the genetic clade 2.3.4.4b, which matches the clade widespread among birds globally. On March 29, 2024, USDA’s National Veterinary Services Laboratories (NVSL) confirmed HPAI in a Michigan dairy herd that had recently received cows from Texas. The USDA Animal and Plant Health Inspection Service (APHIS) is providing ongoing updates on detections in dairy herds, along with information on epidemiological findings and biosecurity guidance for farmers and veterinarians. Preliminary analysis of the A(H5N1) viruses has not identified changes that would make these viruses resistant to current FDA-approved flu antiviral medications, suggesting these treatments are effective against these viruses. Candidate vaccine viruses (CVVs) developed against related clade 2.3.4.4b viruses are available for vaccine manufacturing if necessary, and preliminary analysis suggests they may offer reasonable protection against H5N1 influenza viruses. Seasonal flu vaccines do not offer protection against these viruses. Analysis of virus samples continues.
The CDC is closely working with state and federal agencies, including the USDA, the Food and Drug Administration (FDA), and local health authorities to further investigate and monitor this situation.
