2009 Influenza A (H1N1) virus


  • The H1N1 swine influenza A pandemic of 2009 was caused by a novel reassortant strain of influenza A, containing segments from multiple swine, human, and avian strains of influenza A.
  • With the exception of cases occurring in Mexico early in the pandemic, most cases are a relatively mild, self-limited febrile respiratory illness, similar to seasonal influenza.
  • As with seasonal influenza, infection control measures are critical to limiting the spread of this infection, including frequent handwashing, covering nose and mouth when coughing and sneezing, and using respiratory droplet isolation/contact precautions in the healthcare setting.
  • Testing is not necessary for all patients who present with influenza-like illness. If definitive diagnosis of H1N1 swine influenza must be made, the test of choice is real-time reverse transcriptase-PCR (rRT-PCR) of respiratory specimens or viral culture using panels that probe for human and swine influenza A.
  • Treatment is recommended for patients admitted to the hospital and for patients at higher risk of influenza complications (includes children, pregnant women, and those with comorbid conditions). Treatment should not be withheld in these patients while awaiting test results.

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