UMEM Educational Pearls

Title: Making sense of the H s and N s this flu season

Keywords: influenza, China, Asia, Avian, Swine, Global (PubMed Search)

Posted: 1/12/2014 by Andrea Tenner, MD (Updated: 1/15/2014)
Click here to contact Andrea Tenner, MD

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