CDC: Interim Guidance on Case Definitions to be Used for Novel Influenza A (H7N9)

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CDC . . .

Interim Guidance on Case Definitions to be Used for Novel Influenza A (H7N9) Case Investigations in the United States

This document provides interim guidance for state and local health departments conducting investigations of infections with novel influenza A (H7N9) viruses. The following definitions are for the purpose of investigations of confirmed and probable cases, and cases of novel influenza A (H7N9) virus infection under investigation. CDC is requesting notification of all confirmed and probable cases of novel influenza A (H7N9) virus infection within 24 hours of identification. When possible, state health departments are encouraged to investigate all potential cases of novel influenza A (H7N9) virus infection further to determine case status.

Case Definitions

Confirmed Case: A patient with novel influenza A (H7N9) virus infection that is confirmed by CDC's Influenza Laboratory or a CDC certified public health laboratory using methods agreed upon by CDC and CSTE.¹

Probable Case: A patient with illness compatible with influenza for whom laboratory diagnostic testing is positive for influenza A, negative for H1, negative for H1pdm09, and negative for H3 by real-time reverse transcriptase polymerase chain reaction (RT-PCR), and therefore unsubtypeable.

Case Under Investigation: A patient with illness compatible with influenza meeting either of the following exposure criteria and for whom laboratory confirmation is not known or pending, or for whom test results do not provide a sufficient level of detail to confirm novel influenza A virus infection.

• A patient who has had recent contact (within ≤ 10 days of illness onset) with a confirmed or probable case of infection with novel influenza A (H7N9) virus.
  

OR

• A patient who has had recent travel (within ≤ 10 days of illness onset) to a country where human cases of novel influenza A (H7N9) virus have recently been detected² or where novel influenza A (H7N9) viruses are known to be circulating in animals.
  

Cases under investigation with severe respiratory illness (including radiographically-confirmed pneumonia, acute respiratory distress syndrome (ARDS), or other severe respiratory illness) of unknown etiology may be prioritized for diagnostic testing.

¹ Confirmation of all novel influenza A (H7N9) viruses will initially be performed by CDC's Influenza Laboratory. Once appropriate diagnostic testing methodology has been identified by CDC, confirmation may be made by public health laboratories following CDC-approved protocols for detection of novel influenza A (H7N9) virus, or by laboratories using an FDA-authorized test specific for detection of novel influenza A (H7N9) virus.

² Countries that have recently reported novel influenza A (H7N9) human cases include: China.

For more information, please see the CDC Avian Influenza A (H7N9) Virus information page.

http://www.cdc.gov/flu/avianflu/h7n9-case-definitions.htm