Interim Guidance on Case Definitions for Investigations of Human Infection with Avian Influenza A (H7N9) Virus in the United States

This document provides updated interim guidance for state and local health departments conducting investigations of human infections with avian influenza A (H7N9) viruses. The following definitions are for the purpose of investigations of confirmed and probable cases, and cases of avian influenza A (H7N9) virus infection under investigation. CDC is requesting notification of all confirmed and probable cases of avian influenza A (H7N9) 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.

Case Definitions

Confirmed Case: Avian influenza A (H7N9) 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 avian influenza A (H7N9) virus infections may be made by public health laboratories following CDC-approved protocols for detection of avian influenza A (H7N9) virus, or by laboratories using an FDA-authorized test specific for detection of avian influenza A (H7N9) virus.

Probable Case: Illness compatible with influenza in a patient meeting any of 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 avian influenza A (H7N9) virus infection have become infected or to areas where avian influenza A (H7N9) viruses are known to be circulating in animals (poultry).¹

OR

• 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 (H7N9) 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 case, family members of a confirmed case, persons who lived with or stayed overnight with a confirmed or suspected case, and others who have had similar close physical contact.²

OR

• Unprotected exposure to live avian influenza A (H7N9) virus in a laboratory.

¹ As of January 10, 2014, China was the only country where avian influenza A (H7N9) viruses were known to be circulating in animals (poultry) or where human cases have become infected. For more information, including updates on countries affected, please see the CDC Avian Influenza A (H7N9) Virus information page.

² Limited data are available for avian influenza A (H7N9) virus in which limited non-sustained person-to-person transmission could not be excluded in some family clusters; limited non-sustained person-to-person transmission of highly pathogenic avian influenza A (H5N1) virus has been reported in several countries following close, prolonged unprotected contact with a severely ill H5N1 patient, including in household and hospital settings.

³ Suspected cases of avian influenza A (H7N9) virus infection include probable cases, cases under investigation, and other patients for whom available clinical and epidemiologic information support a diagnosis of infection with avian influenza A (H7N9) virus.