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Influenza
Influenza ("flu") is a contagious viral infection mainly affecting the nose, throat, airways, and lungs. It is one of the most changeable viruses; changes can be small and continuous or abrupt. Flu outbreaks occur yearly, usually from November to March in the Northern Hemisphere. Approximately 5% to 20% of Americans are infected every flu season. Most people improve within a week, but for elderly people, infants and children, and people with some chronic diseases, influenza can be life-threatening. In the United States, seasonal influenza kills more than 36 000 people and hospitalizes 200 000 others yearly. The November 4, 2009, issue of JAMA includes several articles about influenza.
TYPES OF INFLUENZA
Influenza viruses are classified as type A, B, or C. Type A is the most common and causes most of the serious epidemics. It infects many animals, such as ducks, chickens, and pigs, as well as humans. Type B can cause epidemics but these are usually milder than type A influenza. Type C has never been associated with an epidemic. Influenza is not the same as the common cold. Similarly, "stomach flu" is not influenza. The H1N1 influenza virus, or "swine flu," is a new type A influenza virus, probably resulting from an abrupt change in virus structure. It is so different that no one knows how severe it will be in the general population; this leads to concern that it may be particularly virulent (extremely severe). It is currently causing global (pandemic) disease.
TRANSMISSION
Influenza is transmitted from person to person by droplets when infected people cough or sneeze. It is also possible to become infected after touching a surface that has been contaminated by someone who has flu. Those living in crowded conditions or in schools are at greatest risk of infection. People are infectious from one day before symptoms develop until up to five days after becoming sick.
TREATMENT AND PREVENTION
The best defense against influenza is the flu vaccine. A new vaccine is created yearly because influenza viruses change yearly. Flu vaccine for injection is made from killed virus and therefore cannot transmit flu. Side effects of the vaccination may include soreness at the injection site, fever, fatigue, and sore muscles. For vaccine recommendations see the Centers for Disease Control and Prevention Web site. This fall, a separate vaccine against the H1N1 virus will be offered in addition to the normal seasonal flu vaccine. Antiviral medications can be used to treat influenza if given within 48 hours of the first symptoms. Antivirals should not be used in place of flu vaccine. Antibiotics should not be used to treat influenza.
FOR MORE INFORMATION
INFORM YOURSELF
To find this and previous JAMA Patient Pages, go to the Patient Page link on JAMA's Web site at http://www.jama.com. Many are available in English and Spanish.
Sources: Centers for Disease Control and Prevention, National Institutes of Health, World Health Organization
The JAMA Patient Page is a public service of JAMA. The information and recommendations appearing on this page are appropriate in most instances, but they are not a substitute for medical diagnosis. For specific information concerning your personal medical condition, JAMA suggests that you consult your physician. This page may be photocopied noncommercially by physicians and other health care professionals to share with patients. To purchase bulk reprints, call 312/464-0776.
TOPIC: INFECTIOUS DISEASES
Huan J. Chang, MD, MPH, Writer;
Alison E. Burke, MA, Illustrator;
Richard M. Glass, MD, Editor
JAMA. 2009;302(17):1926.
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