LACMA-Blog | CDC Health Advisory: Infecti Influenza Virus Variant


Five cases of human infection with influenza viruses that typically spread only in pigs, also known as variant influenza virus infections, were reported to the CDC in August 2022. These cases include three infections with variant influenza A(H3N2) (A(H3N2)v) virus and two infections with influenza A(H1N2)v virus. These cases have been 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. The clinical features of these cases are similar to those of seasonal influenza infections and include fever, cough, pharyngitis, myalgias 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 variants of influenza virus infection has been identified.

Early identification and investigation of influenza virus variants is important to determine if the virus is spreading effectively among people. Rapid detection and characterization of novel influenza A viruses and efforts to reduce transmission to others remain important components of national efforts to prevent the emergence of novel viruses that could have pandemic potential. To accomplish this, screening for influenza viruses and surveillance for new influenza A virus infections, including variants of influenza virus infection, should continue throughout the year. People, especially those at increased risk of complications from influenza, can take public health measures to limit their risk of infection (eg, limit exposure to infected animals). Clinicians are encouraged to consider variant influenza virus infection as a possible diagnosis when evaluating patients with acute respiratory illness and exposure to pigs or agricultural fairs prior to illness.

Since 2005, 504 variants of influenza virus infection (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. Agricultural fairs are held annually in the United States, primarily during the summer and early fall. Many fairs have pigsties, where pigs from different geographical areas come into close contact with each other and with people. These places can allow influenza viruses to spread among pigs and between pigs and humans. Infected pigs can spread influenza viruses even if they do not show symptoms (eg coughing or sneezing).

The CDC predicts 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 people whose exposure is known to be associated with infection with the variant influenza virus (for example, attendance at agricultural fairs or workers in the hog industry ). New influenza A virus infections, which include those caused by influenza virus variants, are reportable conditions in the United States, and all confirmed cases must be reported to the CDC within 24 hours.

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