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Highly Pathogenic Asian-Origin Avian Influenza A (H5N1) Virus

Highly pathogenic Asian-origin avian influenza A (H5N1) virus – referred to as HPAI H5N1 and sometimes shortened to H5N1 – is a virus that occurs mainly in birds, is highly contagious among birds, and can be deadly to them, especially domestic poultry. Though relatively rare, sporadic human infections with this virus have occurred in Africa, south-east and central Asia, Europe and the Middle East and caused serious illness and death.

Here's a map that shows Highly Pathogenic Avian Influenza (H5N1) Human Cases and Deaths Since 2003 [2.8 MB, 1 page] January 8, 2014

For Health Professionals Practicing in the United States

  • Avian influenza A viruses have rarely caused illness in humans in North America.
  • To date, there have not been any reports of HPAI Asian-origin H5N1 virus infections in people in the United States.
Highly Pathogenic Asian-Origin Avian Influenza (HPAI) A (H5N1)
  • Worldwide, the epidemiology of human infections with HPAI Asian-origin H5N1 virus has not changed significantly since the re-emergence of human cases with this virus infection in 2003.
  • The most common clinical syndrome is fever and cough which in some patients progresses rapidly to several viral pneumonia with shortness of breath, difficulty breathing, and hypoxia.1,2
  • Frequent complications include respiratory failure, acute respiratory distress syndrome (ARDS), multi-organ failure, and death.3
  • CDC continues to recommend that surveillance for suspected human cases of HPAI Asian-origin H5N1 virus infection in the United States remain at an enhanced level.
  • Successful identification of cases depends upon health care providers obtaining information from patients who present with respiratory illness about their recent travel outside of the U.S. and their activities while traveling.
  • CDC recommends that health care providers consider testing for persons that have both a clinical syndrome consistent with HPAI Asian-origin H5N1 disease and relevant possible exposure to HPAI Asian-origin H5N1 virus during the 10 days before the person’s illness onset. Clinicians should notify their state health department immediately when they decide to test a patient for HPAI Asian-origin H5N1 virus infection so that appropriate testing and follow up of contacts is initiated and so that arrangements can be made for properly handling and transporting the specimen to the state health department.
Interim Guidance Documents Specific to HPAI Asian-origin H5N1
Vaccination and Treatment for HPAI Asian-Origin H5N1 in Humans

When to Contact CDC

  • The Influenza Division, CDC, should be contacted immediately for the following things:
    • Any positive results of HPAI Asian-origin H5N1 virus testing.
    • Any questions related to HPAI Asian-origin H5N1 and specimen collection, laboratory testing, antiviral treatment, or infection control.
    • Laboratory results for human clinical specimens that test positive for HPAI Asian-origin H5N1 virus by reverse transcription-polymerase chain reaction (RT-PCR) at a laboratory in the United States should be confirmed immediately at the Influenza Division, National Center for Immunization and Respiratory Diseases, CDC, a designated WHO H5 Reference Laboratory located in Atlanta, Georgia.
    • Before sending specimens, state and local health departments should contact the CDC Influenza Division Epidemiology and Prevention Branch at (404) 639-3747 (Monday – Friday, 8:30 AM - 5:00 PM or the on-call epidemiologist at (770) 488-7100 (all other times).

Bird Importation

  • CDC supports USDA's Animal and Plant Health Inspection Service in its ongoing regulations to prohibit or restrict the importation of birds, poultry, and unprocessed birds and poultry products (such as eggs and feathers) from countries where highly pathogenic avian influenza Asian-origin (HPAI H5N1) has been confirmed in poultry. Visit Bringing a Bird into the United States for more information.


  1. Writing Committee of the Second World Health Organization Consultation on Clinical Aspects of Human Infection with Avian Influenza A (H5N1) Virus, Abdel-Ghafar AN, Chotpitayasunondh T, Gao Z, Hayden FG, Nguyen DH, de Jong MD, Naghdaliyev A, Peiris JS, Shindo N, Soeroso S, Uyeki TM. Update on avian influenza A (H5N1) virus infection in humans. N Engl J Med. 2008 Jan 17;358(3):261-73
  2. Uyeki TM. Human infection with highly pathogenic avian influenza A (H5N1) virus: review of clinical issues. Clin Infect Dis. 2009 Jul 15;49(2):279-90.
  3. World Health Organization Clinical management of human infection with avian influenza A (H5N1) virus. Updated advice 15 August 2007 [116 KB, 22 pages]