Conditions InDepth: Viral Upper Respiratory Infections (Colds and Influenza)
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Conditions InDepth: Viral Upper Respiratory Infections (Colds and Influenza)

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Viral upper respiratory infections come in every degree of severity and cause symptoms in the ears, sinuses, throat, and nose. This report will cover two of the most common respiratory infections: the common cold and influenza (the flu).

The Upper Respiratory Tract

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In the United States the broad category of viral respiratory illness is responsible for at least half of all acute illness, 60%-80% of all school absenteeism, and 30%-50% of all work absenteeism.

Influenza travels around the globe in yearly winter epidemics of varying magnitude. Major epidemics occur every 10-15 years and may kill upwards of 40,000 people in the United States alone each year. Minor epidemics kill "only" about 20,000 in an average year. Most of the deaths occur in people weakened by chronic illnesses, such as heart and respiratory diseases.

The Common Cold

The common cold is characterized by nasal congestion, a runny nose, sneezing, and perhaps a sore throat, headache, and malaise (not feeling well). A fever is unusual. Symptoms resolve on their own usually within 1-2 weeks.

There are at least 200 known viruses responsible for the symptoms of a common cold. Some of these may also affect the lower respiratory tract and cause other conditions. For instance, respiratory syncytial virus can cause severe pneumonia in infants.


Influenza is a very specific illness caused by a single group of influenza viruses. It has a characteristic seasonal cycle that peaks in the winter. It also has typical symptoms, although they vary greatly in severity among cases. It may feel similar to a common cold, but it usually causes a high fever (102°F-104°F), significant malaise, and a dry cough along with a runny nose, headache, muscle ache, and sore throat.

Influenza viruses are divided into three species: A, B, and C. Influenza A is the cause of the worst epidemics. This is because it changes its identity often, so that a person’s previously developed immunity does not recognize the new variation.

International organizations like the World Health Organization (WHO) Epidemic and Pandemic Alert and Response (CSR) team are constantly searching the world for new variations of influenza viruses. Each year they attempt to identify the strains most likely to cause epidemics and make recommendations for developing vaccines against them.

What are the risk factors for colds and influenza?
What are the symptoms of colds and influenza?
How are colds and influenza diagnosed?
What are the treatments for colds and influenza?
Are there screening tests for colds and influenza?
How can I reduce my risk of colds and influenza?
What questions should I ask my healthcare provider?
Where can I get more information about colds and influenza?


Beers MH, Berkow R. The Merck Manual of Diagnosis and Therapy . 17th ed. Hoboken, NJ: John Wiley and Sons; 1999.

Fauci AS, Braunwald E, Isselbacher KJ, et al. Harrison's Principles of Internal Medicine . 14th ed. New York, NY: The McGraw-Hill Companies; 2000.

National Center for Infectious Diseases. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/ncidod/ . Accessed February 1, 2006.

World Health Organization website. Available at: http://www.who.int/en/ . Accessed February 1, 2006.

Last reviewed January 2007 by Kari Kassir, MD

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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