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General Information:
The H’s and N’s refer to hemagglutinin and neuraminidase—two proteins on the surface of the Influenza A virus that help it attach. Here’s a quick breakdown of important emerging strains of influenza:
Avian flu:
- H5N1 (aka. Highly Pathogenic Avian Influenza A): Case Fatality Rate (CFR) 60%, no sustained person to person transmission, primarily in Asia and Middle East--first death in the Americas occurred in Canada last week (returned traveller from China)
- H7N9: new strain of avian influenza identified this year, 135 cases so far, CFR 33%, no sustained person to person transmission, found in China
Swine flu:
- H1N1: pandemic flu of 2009 making a comeback. causes more severe disease in young and middle-aged adults, predominant this season in the US (of subtyped virus tests ~98% were H1N1)
Relevance to the EM Physician:
As the frontline against the flu virus, we should know what to expect. H1N1 has predominated this flu season—so far 60% of hospitalizations occurred in patients aged 18-64, which is unusual. H7N9 is new on the scene but might be imported, and H5N1 has arrived.
Bottom Line:
Expect to see more severe illness in the 18-64 y/o age group due to H1N1. Watch for more deadly flu imports--obtain a travel history and notify the CDC of severe influenza-like illness in returned travellers.
University of Maryland Section of Global Emergency Health
Author: Andi Tenner, MD, MPH, FACEP
References
http://www.cdc.gov/flu/avianflu/h5n1-people.htm
http://www.cdc.gov/flu/weekly/summary.htm
http://www.cdc.gov/flu/avianflu/h7n9-virus.htm