The flu is a contagious infection of the nose, throat, and lungs caused by the influenzavirus.
Alternative Names
Flu; Influenza A; Influenza B
Causes, incidence, and risk factors
In temperate climates, influenza A usually arrives between early winter and early spring. Influenza B can appear at any time of the year.
The most common way to catch the flu is by breathing in droplets from coughs or sneezes. Less often, it is spread when you touch a surface such as a faucet handle or phone that has the virus on it, and then touch your own mouth, nose, or eyes.
Symptoms appear 1 - 7 days later (usually within 2 - 3 days). Because the flu spreads through the air and is very contagious, it often strikes a community all at once, causing an epidemic illness. This creates a cluster of school and work absences. Many students become sick within 2 or 3 weeks of the flu's arrival in a school.
Tens of millions of people in the United States get the flu each year. Most get better within a week or two, but thousands become sick enough to be hospitalized. About 36,000 people die each year from complications of the flu.
Sometimes people confuse colds and flu, which share some of the same symptoms and typically occur at the same time of the year. However, the two diseases are very different. Most people get a cold several times each year, and the flu only once every few years.
Common cold (3 images)
Average Rating:
(Doctor-Reviewed information)
The common cold generally involves a runny nose, nasal congestion, and sneezing. You may also have a sore throat, cough, headache, or other symptoms. Reviewer: Linda Vorvick, MD, Family Physician, Seattle Site Coordinator, Lecturer, Pathophysiology, MEDEX Northwest Division of Physician Assistant Studies, University of Washington School of Medicine; and David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc. Date: 03/06/2009
Sore throat (2 images)(Doctor-Reviewed information)
A sore throat is discomfort, pain, or scratchiness in the throat. A sore throat often makes it painful to swallow.Sore throats are common. Reviewer: Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc. Date: 12/01/2008
Nasal congestion (1 image)(Doctor-Reviewed information)
Nasal congestion refers to a stuffy nose. Many people think that a nose gets congested(stuffy) from too much thick mucus. Reviewer: Daniel Rauch, M.D., FAAP., Director, Pediatric Hospitalist Program, New York University School of Medicine, New York, NY. Review provided by VeriMed Healthcare Network.Date: 10/23/2007
Cough (1 image)(Doctor-Reviewed information)
Coughing is an important way to keep your throat and airways clear. However, excessive coughing may mean you have an underlying disease or disorder.Some coughs are dry, while others are considered productive. Reviewer: David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc. Previously reviewed by Andrew Schriber, MD, FCCP, Specialist in Pulmonary, Critical Care, and Sleep Medicine, Virtua Memorial Hospital, Mount Holly, New Jersey. Review provided by VeriMed Healthcare Network (11/12/2007).Date: 01/18/2008
Influenza vaccine (2 images)(Doctor-Reviewed information)
This vaccine protects people against the flu.Vaccine- influenza; Immunization- influenza; Flu shot; Flu vaccine.The flu is a contagious respiratory disease caused by an influenza virus. In the U.S., flu outbreaks typically occur in winter mo...Reviewer: A.D.A.M. Editorial Team: David Zieve, MD, MHA, Greg Juhn, MTPW, David R. Eltz. Previously reviewed by David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine (6/18/2008).Date: 08/05/2008
Strep throat (2 images)(Doctor-Reviewed information)
Strep throat is caused by Group A Streptococcus bacteria. It is the most common bacterial infection of the throat.Pharyngitis- streptococcal; Streptococcal pharyngitis.Strep throat is most common in children between the ages of 5 and 15, although ...Reviewer: Linda Vorvick, MD, Family Physician, Seattle Site Coordinator, Lecturer, Pathophysiology, MEDEX Northwest Division of Physician Assistant Studies, University of Washington School of Medicine; and Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.Date: 03/14/2009
Fever (2 images)(Doctor-Reviewed information)
Fever is the temporary increase in the body''s temperature, in response to some disease or illness.A child has a fever when their temperature is at or above one of these levels:.100.4°F(38°C) measured in the bottom(rectally) 99.5°F(3...Reviewer: A.D.A.M. Editorial Team: David Zieve, MD, MHA, Greg Juhn, MTPW, David R. Eltz. Previously reviewed by Rachel A. Lewis, MD, FAAP, Columbia Pediatric Faculty Practice, New York, NY. Review provided by VeriMed Healthcare Network (2/27/2008).Date: 04/17/2009
Sneezing (1 image)(Doctor-Reviewed information)
A sneeze is a sudden, forceful, involuntary burst of air through the nose and mouth.Reviewer: Stuart I. Henochowicz, MD, FACP, Associate Clinical Professor of Medicine, Division of Allergy, Immunology, and Rheumatology, Georgetown University Medical School. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.Date: 09/09/2008
Diarrhea (4 images)(Doctor-Reviewed information)
Diarrhea is loose, watery, and frequent stool. Diarrhea is considered chronic(long-term) when you have had loose or frequent stools for more than 4 weeks.Stools- watery; Frequent bowel movements; Loose bowel movements.Diarrhea in adults is usually...Reviewer: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc. Date: 02/19/2009
Sinusitis (2 images)(Doctor-Reviewed information)
Sinusitis refers to inflammation of the sinuses that occurs with a viral, bacterial, or fungal infection.Acute sinusitis; Sinus infection; Sinusitis- acute; Sinusitis- chronic; Rhinosinusitis.The sinuses are air-filled spaces in the skull(behind t...Reviewer: Alan Lipkin, MD, Otolaryngologist, Private Practice, Denver, Colorado. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.Date: 04/21/2009
Vitamin C and colds (1 image)(Doctor-Reviewed information)
Despite the popular belief that vitamin C can cure the common cold, the scientific evidence for this is conflicting.Large doses of vitamin C, for example, may help reduce the duration of a cold, but they do not appear to protect against one in the...Reviewer: Charlotte Grayson, MD, Private Practice specializing in Internal Medicine, Smyrna, GA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.Date: 08/08/2008
Flu and holidays(Doctor-Reviewed information)
Why is the flu more common during the winter holiday season?The combination of being indoors more frequently, being exposed to more people at social occasions, and being under increased stress during the winter holidays can explain the higher inci...Reviewer: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc. Date: 02/19/2009
Colds and flus - antibiotics(Doctor-Reviewed information)
Antibiotics will fight bacterial infections, but do not treat viral infections like colds and the flu. So unless you have a bacterial infection, do NOT take antibiotics. Reviewer: Rachel A Lewis, MD, FAAP, Columbia University Pediatric Faculty Practice, New York, NY. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.Date: 07/24/2008
Exercise - colds and flu (2 images)(Doctor-Reviewed information)
Yes. At least one study suggests that regular exercise can cut in half the number of days a person suffers from colds and the flu. Reviewer: Linda Vorvick, MD, Family Physician, Seattle Site Coordinator, Lecturer, Pathophysiology, MEDEX Northwest Division of Physician Assistant Studies, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.Date: 02/22/2009
Treatment - cold symptoms (1 image)(Doctor-Reviewed information)
Zinc lozenges may reduce the duration and intensity of cold symptoms, but reports are mixed. In general, each symptom of a cold may be treated separately.Reviewer: Linda Vorvick, MD, Family Physician, Seattle Site Coordinator, Lecturer, Pathophysiology, MEDEX Northwest Division of Physician Assistant Studies, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.Date: 02/22/2009
Avian influenza(Doctor-Reviewed information)
Avian influenza is flu infection in birds. The disease is of concern to humans, who have no immunity against it. Reviewer: Linda Vorvick, MD, Family Physician, Seattle Site Coordinator, Lecturer, Pathophysiology, MEDEX Northwest Division of Physician Assistant Studies, University of Washington School of Medicine; and David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc. Date: 03/06/2009
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