The New Avian Influenza A (H7N9) Virus: What Clinicians Should Know

Alicia M. Fry, MD, MPH


May 09, 2013

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Case Investigation and Testing

Interim recommendations for clinicians and state and local health departments for case investigation and testing for suspected infections with novel influenza A (H7N9) viruses can be found in Health Alert Network Advisory: Human Infections with Novel Influenza A (H7N9) Viruses.

The HAN Advisory includes the following recommendations:

Patients with illness compatible with influenza who also meet either of the exposure criteria below should be candidates for reverse-transcription polymerase chain reaction (RT-PCR) testing for influenza.

Exposure criteria (as of April 24, 2013):

   ♦ Patients with recent travel to countries where human cases of novel H7N9 virus infection have recently been detected, especially if there was recent direct or close contact with animals (such as wild birds, poultry, or pigs) or where novel H7N9 viruses are known to be circulating in animals.

   ♦ Patients who have had recent contact with confirmed human cases of infection with novel H7N9 virus.

Clinicians should obtain a nasopharyngeal swab or aspirate from these patients, place the swab or aspirate in viral transport medium, and contact their state or local health department to arrange transport and request a timely diagnosis at a state public health laboratory or CDC. Patients with pneumonia may require a lower respiratory specimen (eg, endotrachial aspirate or bronchoalveolar lavage). Visit the CDC Website for more information on specimen collection and diagnostic testing.

If infection with H7N9 virus is suspected based on current clinical and epidemiologic screening criteria recommended by public health authorities, specimens should be collected with appropriate infection control precautions for novel virulent influenza viruses and sent to the state or local health department for testing. Viral culture should not be attempted in these cases.

All unsubtypable influenza A virus specimens should be submitted to CDC immediately for additional diagnostic testing. At this time, confirmatory testing for H7N9 will be conducted at CDC.

Commercially available rapid influenza diagnostic tests (RIDTs) may not detect avian or variant influenza A viruses in respiratory specimens. Therefore, a negative RIDT result does not exclude infection with influenza viruses. In addition, a positive test result for influenza A cannot confirm variant or avian influenza virus infection because these tests cannot distinguish between influenza A virus subtypes (they do not differentiate between human influenza A viruses and avian or variant viruses). Therefore, when RIDTs are positive for influenza A and there is concern for novel influenza A virus infection, respiratory specimens should be collected and sent for RT-PCR testing at a state public health laboratory. Clinical treatment decisions should not be made on the basis of a negative RIDT result because the test has only moderate sensitivity for seasonal flu and unknown sensitivity for novel H7N9 viruses.