The common cold is a viral infection of the lining of the nose, sinuses, throat, and large airways.

Common colds are among the most common illnesses. Many different viruses cause colds, but the rhinoviruses (of which there are 100 subtypes) are implicated more often than others. Colds caused by rhinoviruses occur more commonly in the spring and fall; different viruses cause colds during other times of the year.

Colds mainly spread when a person's hands come in contact with nasal secretions from an infected person. These secretions contain cold viruses. When the person touches his mouth, nose, or eyes, the viruses gain entry to the body and produce a new cold. Less often, colds are spread when a person breathes air that contains droplets that were coughed or sneezed out by an infected person. A cold is most contagious in the first 1 or 2 days after symptoms develop. Becoming chilled does not cause colds, nor does it increase a person's susceptibility to infection. A person's general health and eating habits also do not seem to affect susceptibility to infection, nor does having an abnormality of the nose or throat (such as enlarged tonsils or adenoids).

Symptoms and Diagnosis

Symptoms of the cold start 1 to 3 days after infection. Usually, the first symptom is discomfort in the nose or throat. Later, the person starts sneezing, has a runny nose, and feels mildly ill. Fever is not common, but a mild fever may develop at the beginning of the illness. At first, the secretions from the nose are watery and clear and can be annoyingly plentiful; eventually they become thicker, opaque, yellow-green, and less abundant. Many people also develop a cough. Symptoms usually disappear in 4 to 10 days, although a cough often lasts into the second week.

Complications may prolong the illness. Rhinovirus infection often triggers asthma attacks in people with asthma. Some people develop bacterial infections of the middle ear (otitis media) or sinuses because of a cold. These infections develop because congestion in the nose blocks the normal drainage of those areas, allowing bacteria to grow in collections of blocked secretions. Other people develop bacterial infections of the lower airways (secondary bronchitis or pneumonia).

Doctors are usually able to diagnose a cold from the typical symptoms. A high fever, severe headache, rash, difficulty breathing, or chest pain suggests that the infection is not a simple cold. Laboratory tests usually are not needed to diagnose a cold. If complications are suspected, doctors may order blood tests and x-rays.

Prevention

Because so many different viruses cause colds and because each virus changes slightly over time, an effective vaccine has not yet been developed. The best preventive measure is practicing good hygiene. Because many cold viruses are spread through contact with the secretions of an infected person, both the sick person and the people in his household and office should wash their hands frequently. Sneezing and coughing should be done into tissues, which should then be carefully disposed of. When possible, the sick person should sleep in a separate room. People who are coughing or sneezing from a cold should not go to work or school where they might infect others. Cleaning shared objects and surfaces can also help to reduce the spread of common cold viruses.

Despite their popularity, echinacea and high-dose vitamin C (up to 2,000 milligrams per day) have not been shown to prevent colds. When sprayed into the nose, the substance interferon reduces the chance of acquiring a rhinovirus cold. However, interferon causes irritation and bleeding of the nose and does not work against other cold viruses. Interferon nasal spray is not commercially available in the United States.

Treatment

A person with a cold should stay warm and comfortable and try to avoid spreading the infection to others. Anyone with a fever or severe symptoms should rest at home. Drinking fluids and inhaling steam or mist from a vaporizer may help to keep secretions loose and easier to expel.

Currently available antiviral drugs are not effective against colds. An experimental antiviral drug called pleconaril (PICOVIR) reduces the duration and severity of cold symptoms and may become available in the near future. Antibiotics do not help people with colds, even when the nose or cough produces colored mucus.

Echinacea (see Medicinal Herbs and Nutraceuticals: Echinacea), zinc preparations, and vitamin C have been suggested as therapy for colds. Small studies have shown them to be effective, but the effectiveness has not been confirmed in rigorous, large clinical studies.

Several popular nonprescription remedies that help the symptoms of a cold are available (see Over-the-Counter (OTC) Drugs: Cold Remedies). Because they do not cure the infection, which usually resolves after a week anyway, doctors feel that their use is optional, depending on how bad the person feels. Several different types of drugs are used to relieve cold symptoms: decongestants help open clogged nasal passages, antihistamines help dry a runny nose, and cough syrups make coughing easier by thinning secretions or suppressing cough. These drugs are most often sold as combinations but can also be obtained individually. Antihistamines can cause drowsiness and are particularly problematic in older people.

Aspirin is generally not recommended for children because in that age group it is associated with an increased risk of Reye's syndrome. Cough suppressants are not routinely recommended because coughing is a good way to clear secretions and debris from the airways during a viral infection. However, a severe cough that interferes with sleep or causes great discomfort can be treated with a cough suppressant.

Courtesy: The Merck Manuals