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2009 MAY–JUNE No. 368
May 13, 2009 [posted]

2009 H1N1 Flu ("Swine Flu") Terminology

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During the recent outbreak of H1N1 influenza in humans, the term "swine flu" has become prevalent in the professional literature and especially the public media. The inherent ambiguous nature of this expression leads to major confusion. Despite the name, the new influenza virus has been mostly isolated from infected humans, though many of its genes are derived from pig viruses.

On April 30, 2009, the Centers for Disease Control and Prevention officially designated the name of the virus as Swine-origin Influenza A (H1N1) Virus.

MeSH® Headings

On May 1, 2009, MeSH added the new term to an existing descriptor:

Existing Descriptor: INFLUENZA A VIRUS, H1N1 SUBTYPE
         New entry term: Swine-Origin Influenza A H1N1 Virus

Additionally, to avoid confusion, MeSH deleted the entry term "Swine Influenza Virus" from the descriptor INFLUENZA A VIRUS. This referred to the classical swine flu virus which has evolved since developing in pigs during the 1918 Spanish flu pandemic.


If an article on "swine flu in humans" refers to the H1N1 subtype, the indexing will be: INFLUENZA, HUMAN + INFLUENZA A VIRUS, H1N1 SUBTYPE + HUMANS

An article on "swine flu of the H1N1 subtype in swine" will be indexed as: INFLUENZA A VIRUS, H1N1 SUBTYPE + ORTHOMYXOVIRIDAE INFECTIONS + SWINE. Since other viral subtypes besides H1N1 can cause swine flu in swine, index with other subtypes as appropriate or with INFLUENZA A VIRUS if no specific subtype is stated or implied by the article.

Some articles with "swine flu" in the title include no discussion of a specific virus at all. Such articles are often about the general probability of an upcoming human influenza pandemic and its prevention and control. Indexing for such articles will include:

INFLUENZA, HUMAN + HUMANS (and possibly DISEASE OUTBREAKS (entry term = PANDEMICS); QUARANTINE; PATIENT ISOLATION; or INTERNATIONAL COOPERATION; (if these concepts are substantively discussed).

Searching PubMed®

PubMed will map the search query, i.e., swine flu, to both INFLUENZA, HUMAN and SWINE. Including the phrase H1N1 in your query, swine flu H1N1, will achieve more precise retrieval.

Searchers may also consider using swine flu [tw] in their strategy to retrieve articles that are about potential pandemic in humans, but do not include a substantive discussion of a specific virus or the disease in swine.

By Allan Savage
MeSH Section

Savage A. 2009 H1N1 Flu ("Swine Flu") Terminology. NLM Tech Bull. 2009 May-Jun;(368):e5.