Interim Guidance on Case Definitions for Investigations of Human Infection with Highly Pathogenic Avian Influenza A (H5N1) Virus in the United States
This guidance pertains to Asian H5N1, a virus associated with severe disease in humans, primarily in Asia and Africa.
This document provides interim guidance for state and local health departments conducting investigations of human infections with highly pathogenic avian influenza A (H5N1) viruses. The following definitions are for the purpose of investigations of confirmed and probable cases, and cases of highly pathogenic avian influenza A (H5N1) virus infection under investigation. CDC is requesting notification of all confirmed and probable cases of highly pathogenic avian influenza A (H5N1) virus infection within 24 hours of identification. State health departments are encouraged to investigate all persons who meet testing recommendations for avian influenza A (H7N9) virus infection in the United States, to determine their case status.
Confirmed Case: Highly pathogenic avian influenza A (H5N1) virus infection in a patient that is confirmed by CDC’s Influenza Laboratory or a CDC certified public health laboratory using methods agreed upon by CDC and CSTE. Confirmation of infection with avian influenza A (H5N1) viruses may be made by public health laboratories following CDC-approved protocols for detection of avian influenza A (H5N1) virus, or by laboratories using an FDA-authorized test specific for detection of avian influenza A (H5N1) virus.
Probable Case: Illness compatible with influenza in a patient meeting the exposure criteria below and for whom laboratory diagnostic testing is positive for influenza A, negative for H1, negative for H1pdm09, and negative for H3 by real-time reverse transcription polymerase chain reaction (RT-PCR) and therefore unable to be subtyped.
Case Under Investigation: Illness compatible with influenza in a patient meeting any of the exposure criteria below and for whom confirmatory laboratory test results are not known or pending.
- Patients with recent travel (within <10 days of illness onset) to areas where human cases of highly pathogenic avian influenza A (H5N1) virus infection have become infected or to areas where highly pathogenic avian influenza A (H5N1) viruses are known to be circulating in animals.1
- Patients who have had recent close contact (within <10 days of illness onset) with confirmed or suspected3 cases of human infection with avian influenza A (H5N1) virus. Close contact may be regarded as coming within about 6 feet (2 meters) of a confirmed or suspected case while the case was ill (beginning 1 day prior to illness onset and continuing until resolution of illness). This includes healthcare personnel providing care for a confirmed or suspected case, family members of a confirmed or suspected case, persons who lived with or stayed overnight with a confirmed or suspected case, and others who have had similar close physical contact.2
- Unprotected exposure to live highly pathogenic avian influenza A (H5N1) virus in a laboratory.
1Outbreaks of Highly Pathogenic Avian Influenza (subtype H5N1) in poultry notified to the OIE from the end of 2003 to 2 January 2014 [143 KB, 1 page] and Cumulative Number of Confirmed Human Cases for Avian Influenza A(H5N1) Reported to WHO, 2003-2013 [40 KB, 2 pages].
2 Limited non-sustained person-to-person transmission of highly pathogenic avian influenza A (H5N1) virus has been reported in several countries only following close, prolonged unprotected physical contact with a severely ill H5N1 patient.
3 Suspected cases of influenza A (H5N1) virus infection include probable cases, cases under investigation, and other patients for whom available clinical and epidemiologic information support a diagnosis of infection with highly pathogenic avian influenza A (H5N1) virus.
- Page last reviewed: January 10, 2014
- Page last updated: January 26, 2016
- Content source:
- Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases (NCIRD)
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