Swine Flu (Swine Influenza A (H1N1) Virus)
Key points
- The swine influenza A (H1N1) virus that has infected humans in the U.S. and Mexico is a novel influenza A virus that has not previously been identified in North America.
- Although uncomplicated influenza-like illness (fever, cough or sore throat) has been reported in many cases, mild respiratory illness (nasal congestion, rhinorrhea) without fever and occasional severe disease also has been reported.
- Persons with swine influenza A (H1N1) virus infection should be considered potentially contagious for up to 7 days following illness onset.
- A suspected case of swine influenza A (H1N1) virus infection is defined as a person with acute febrile respiratory illness with onset within 7 days of close contact with a person who is a confirmed case of swine influenza A (H1N1) virus infection.
What is the swine flu?
The swine influenza A (H1N1) virus that has infected humans in the U.S. and Mexico is a novel influenza A virus that has not previously been identified in North America. This virus is resistant to the antiviral medications amantadine (Symmetrel) and rimantadine (Flumadine), but is sensitive to oseltamivir (Tamiflu) and zanamivir (Relenza). Investigations of these cases suggest that on-going human-to-human swine influenza A (H1N1) virus is occurring.
What are the symptoms of swine flu?
Although uncomplicated influenza-like illness (fever, cough or sore throat) has been reported in many cases, mild respiratory illness (nasal congestion, rhinorrhea) without fever and occasional severe disease also has been reported. Other symptoms reported with swine influenza A virus infection include vomiting, diarrhea, myalgia, headache, chills, fatigue, and dyspnea. Conjunctivitis is rare, but has been reported. Severe disease (pneumonia, respiratory failure) and fatal outcomes have been reported with swine influenza A virus infection. The potential for exacerbation of underlying chronic medical conditions or invasive bacterial infection with swine influenza A virus infection should be considered.
Interm Recommendations
For clinical care or collection of respiratory specimens from a symptomatic individual (acute respiratory symptoms with or without fever) who is a confirmed case, or a suspected case (ill close contact of a confirmed case) of swine influenza A (H1N1) virus infection:
Infectious Period
Persons with swine influenza A (H1N1) virus infection should be considered potentially contagious for up to 7 days following illness onset. Persons who continue to be ill longer than 7 days after illness onset should be considered potentially contagious until symptoms have resolved. Children, especially younger children, might potentially be contagious for longer periods. The duration of infectiousness might vary by swine influenza A (H1N1) virus strain. Non-hospitalized ill persons who are a confirmed or suspected case of swine influenza A (H1N1) virus infection are recommended to stay at home (voluntary isolation) for at least the first 7 days after illness onset except to seek medical care.
Case definitions
A confirmed case of swine influenza A (H1N1) virus infection is defined as a person with an acute respiratory illness with laboratory confirmed swine influenza A (H1N1) virus infection at CDC by one or more of the following tests:
- real-time RT-PCR
- viral culture
- four-fold rise in swine influenza A (H1N1) virus-specific neutralizing antibodies
Written and revised by
David Cohen, M.D.
Our doctors write and review articles for accuracy and keep them up to date.
health.am provides general information, not medical advice. Always consult a qualified health professional about your own health.
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