Clinlab Navigator

Influenza H7N9

Novel influenza A viruses are influenza viruses that are different from currently circulating human influenza A virus subtypes and include influenza viruses from predominantly avian and swine origin. In recent years, human infections with highly pathogenic avian influenza A (H5N1) virus in several Asian countries and Egypt, highly pathogenic avian influenza A (H7N3) virus in Mexico, and variant influenza A (H3N2)v viruses in the United States have been reported.

As of April 29, 2013, Chinese public health officials have reported 126 cases of human infection with a novel avian influenza A (H7N9) virus from eight different provinces in China. Most infections involve adults with a median age of 61 years. All patients were hospitalized with severe respiratory illness, and 21% have died of ARDS or multi-organ failure. These are the first human infections identified with an avian influenza A (H7N9) virus infection. No person-to-person transmission has been confirmed. At this time, no cases of human infection with avian influenza A (H7N9) viruses have been detected in the United States.

Chinese investigators have posted 19 partial or complete genome sequences from avian influenza A(H7N9) viruses to a publicly available database at the Global Initiative on Sharing All Influenza Data ( These studies indicated that the hemagglutinin gene (the 'H' in H7N9) and the neuraminidase gene (the 'N' in H7N9) appear to have come from wild ducks in the east Asian flyway that includes eastern China, South Korea, and Japan.The six internal genes of the virus that are named PB1, PB2, PA, NP, M, and NS – all cluster together with genes from at least two different H9N2 viruses isolated from chickens in China. Altogether, these findings suggest at least four sources and multiple re-assortments were needed to produce the current strain of H7N9 virus (Liu D, et al "Origin and diversity of novel avian influenza A H7N9 viruses causing human infection: phylogenetic, structural, and coalescent analyses" Lancet 2013; DOI: 10.1016/S0140-6736(13)60938-1).

Commercially available rapid influenza diagnostic tests may not detect avian or variant influenza A viruses in respiratory specimens. Therefore, a negative rapid influenza diagnostic test 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. Clinical treatment decisions should not be made on the basis of a negative rapid influenza diagnostic test result since the test has only moderate sensitivity.

When rapid influenza diagnostic tests are positive for influenza A and there is concern for novel influenza A virus infection, respiratory specimens should be collected with a nasopharyngeal swab or aspirate, placed in viral transport media and sent for RT-PCR testing. Patients with novel influenza A (H7N9) virus infections should have a positive RT-PCR for influenza A virus but not be subtypeable. All unsubtypeable influenza A virus specimens need to be submitted to CDC immediately for additional diagnostic testing. Suspected infections with novel influenza A (H7N9) viruses in the United States should be reported to CDC within 24 hours of initial detection.

CDC has developed a new H7 diagnostic test for use with the existing CDC influenza rRT-PCR kit. This new H7 test has been cleared by the Food and Drug Administration for use as an in vitro diagnostic test under an Emergency Use Authorization (MMWR, May 1, 2013 / 6;1-6).

For more information on how influenza viruses undergo reassortment to form novel viruses, see

AddThis Social Bookmark Button