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Variant Influenza Virus Infections

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Variant Influenza Virus Infections – Recommendations for Identification, Treatment, and Prevention for Summer and Fall 2022

Health advisory

September 2, 2022

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  • Be aware that human infections with variant influenza viruses which usually spread in pigs were reported to the Centers for Disease Control and Prevention (CDC) in August 2022
  • Ask patients with suspected influenza if they have any recent exposure to swine 
  • Clinicians who suspect influenza in persons with recent exposure to swine should:
    • Obtain a nasopharyngeal swab or aspirate from the patient, 
    • Place the swab or aspirate in a viral transport medium, and 
    • Immediately report suspect variant influenza to Public Health – Seattle & King County at 206-296-4774 and request approval for testing at the Washington State Public Health Lab
  • Recommend antiviral treatment in patients with suspected or confirmed variant influenza virus infection who are hospitalized, have severe illness, or are in a group considered at increased risk for complications from influenza 
  • Consider antiviral treatment for those not at increased risk based on clinical judgement and if treatment can be initiated within 48 hours of illness onset
  • Practice appropriate infection control and adhere to droplet and standard precautions for suspected or confirmed cases

Five cases of human infection with influenza viruses that usually spread only in pigs, also known as variant influenza virus infections, were reported to CDC in August 2022. These cases include three infections with influenza A(H3N2) variant (A(H3N2)v) virus and two infections with influenza A(H1N2)v virus. These cases were identified in West Virginia (3), Oregon (1), and Ohio (1). Four of the five cases reported exposure to pigs or attendance at an agricultural fair prior to illness, and one reported no contact with pigs or attendance at an agricultural fair prior to illness. Clinical characteristics of these cases have been similar to those of seasonal influenza infections and have included fever, cough, pharyngitis, myalgia, and headache. No hospitalizations or deaths have occurred among these five cases, and all patients are recovering or have recovered from their illnesses. To date, no person-to-person spread associated with the five recent variant influenza virus infections has been identified.

Since 2005, 504 variant influenza virus infections (of different influenza A virus subtypes) have been identified in the United States; most of these infections have been associated with exposure to pigs or attendance at an agricultural fair prior to illness onset. CDC anticipates that state health departments may identify more cases of infection with variant influenza viruses in 2022 as the agricultural fair season continues. Testing for variant influenza viruses should focus primarily on persons with exposures known to be associated with variant influenza virus infection (e.g., agricultural fair attendance or workers in the swine industry). Novel influenza A virus infections, which include those caused by variant influenza viruses, are notifiable conditions in the United States, and all confirmed cases should be reported to CDC within 24 hours.

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