• Highlights
• Introduction
• Diagnosis
• Complications
• Risk Factors
• Prevention
• Treatment
• Medications
• Resources
• References

Colds and the flu

Description

An in-depth report on the diagnosis, treatment, and prevention of colds and flu.

Alternative Names

Influenza; Strep throat; Bird flu; Avian influenza

Introduction

Upper respiratory tract infections affect the airways in the nose, ears, and throat.

The infections can be caused by viruses, bacteria, or other microscopic organisms. In most cases, these infections lead to colds or mild influenza (flu) and are temporary and harmless. In rare cases, flu can be severe, or the infections may turn into pneumonia.

Organisms that cause these upper respiratory tract infections are generally spread by:

• Direct contact (such as hand-to-mouth)
• Coughing or sneezing

The Common Cold

The common cold (medically known as infectious nasopharyngitis) is the most common upper respiratory tract infection. More than 200 viruses can cause colds. The most common cause is the rhinovirus, which is responsible for about half of all colds. Symptoms usually develop 1 - 3 days after being exposed to the virus.

A cold usually progresses in the following manner:

• It nearly always starts rapidly with throat irritation and stuffiness in the nose.
• Within hours, full-blown cold symptoms usually develop, which can include sneezing, mild sore throat, fever, minor headaches, muscle aches, and coughing.
• Fever is low-grade or absent. In small children, however, fever may be as high as 103° F for 1 or 2 days. It should go down after that and be normal by the 5th.
• Nasal discharge is usually clear and runny the first 1 - 3 days. It then thickens and becomes yellow to greenish.
• The sore throat is usually mild and lasts only about a day. A runny nose usually lasts 2 - 7 days, although coughing and nasal discharge can persist for more than 2 weeks.

Influenza (The "Flu")

Symptoms. Patients usually feel sick 1 - 4 days after exposure to the influenza (flu) virus. The flu usually involves:

• Abrupt onset of severe symptoms, which include headache, muscle aches, fatigue, and high fever (up to 104° F).
• Cough (which is usually dry but can be severe) and sometimes a runny nose and sore throat.
• Children may experience vomiting, diarrhea, and ear infections, as well as other flu symptoms.
• The symptoms usually resolve in 4 - 5 days, although some people can experience coughing and feelings of illness for more than 2 weeks. In some cases, flu can become more severe or make other conditions worse.

Transmitting the Virus. The virus is spread primarily when a person with the flu coughs or sneezes near someone else. Adults with flu typically spread it to someone else from 1 day before symptoms start to about 5 days after symptoms develop. Children can spread the infection for more than 10 days after symptoms begin, and young children can transmit 6 days or even earlier before the onset of symptoms. People with severely compromised immune systems can transmit the virus for weeks to months.

Flu Strains. A virus is a cluster of genes wrapped in a protein membrane, which is coated with a fatty substance that contains molecules called glycoproteins. Strains of the flu are identified according to the number of membranes and type of glycoproteins present.

The two major flu strains are referred to as A and B:

• Influenza A is the most widespread and can even infect animals and humans. Influenza A is the cause of the major pandemics (worldwide epidemics) of influenza that have occurred. It is usually further categorized by two subtypes based on two substances that occur on the surface of the viruses: hemagglutinin (H) and neuraminidase (N).
• Influenza B infects only humans. It is less common than Type A, but is often associated with specific outbreaks, such as in nursing homes.

Based on a final analysis of the 2001 - 2002 flu season, nearly 90% of flu cases were type A, and about 10% were type B. Influenza A usually causes more severe disease than type B. There is some concern, however, that since influenza B has been less common in the past few years, some people, particularly small children, may have fewer antibodies to it and so may be at higher risk for severe infection.

Avian Influenza (Bird Flu)

Although the risk of lethal viruses is generally low, scientists are greatly concerned about a particular virus called H5N1, which causes avian influenza (bird flu). Since 1997, the H5N1 virus has triggered deadly outbreaks in poultry across Southeast Asia. As of January 22, 2007, 269 people had been infected with the bird flu in 11 countries. More than half of these people have died, according to the World Health Organization. No cases have been seen in the United States.

So far, the virus has spread from birds to humans. The virus does not seem to be easily spread from person to person. However, scientists and public health officials are monitoring the spread of H5N1 and working to contain it. Efforts include slaughtering infected birds, developing new vaccines, and stockpiling antiviral drugs such as oseltamivir (Tamiflu). Many poor nations have limited resources and already contend with other serious health problems, including HIV-AIDS. If H5N1 does mutate and spread, the consequences could be especially severe for these countries.

• Review Date: 3/6/2007
• Reviewed By: A.D.A.M. Editorial Team: Greg Juhn, M.T.P.W., David R. Eltz, Kelli A. Stacy. Previously reviewed by Harvey Simon, MD, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital (12/4/2006).

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