The Common Cold
Source: National Institute of Allergy and Infectious Diseases, National Institutes of Health.
The problem. In the course of a year, individuals in the United States suffer one billion colds, according to some estimates. Adults average about two to four colds a year, although the range varies widely. Women, especially those aged 20–30 years, have more colds than men, possibly because of their closer contact with children. On average, individuals older than 60 have fewer than one cold a year. Colds are most prevalent among children, and seem to be related to youngsters' relative lack of resistance to infection and to contacts with other children in day-care centers and schools. Children have about six to ten colds a year. In families with children in school, the number of colds per child can be as high as 12 a year.
The causes: viruses. More than 200 different viruses are known to cause the symptoms of the common cold. Rhinoviruses (from the Greek rhin, meaning “nose”) cause an estimated 30% to 35% of all adult colds, and are most active in early fall, spring and summer. More than 110 distinct rhinovirus types have been identified. Coronaviruses are believed to cause a large percentage of all adult colds. They induce colds primarily in the winter and early spring. Of the more than 30 isolated strains, three or four infect humans.
Does cold weather cause a cold? Although many people are convinced that a cold results from exposure to cold weather, or from getting chilled or overheated, these conditions in fact have little or no effect on the development or severity of a cold.
How cold viruses cause disease. Viruses cause infection by overcoming the body's complex defense system. The body's first line of defense is mucus, produced by the membranes in the nose and throat. Mucus traps the material we inhale: pollen, dust, bacteria, and viruses. When a virus penetrates the mucus and enters a cell, it commandeers the protein-making machinery to manufacture new viruses, which, in turn, attack surrounding cells.
Cold symptoms: the body fights back. Cold symptoms are probably the result of the body's immune response to the viral invasion. Virus-infected cells in the nose send out signals that recruit specialized white blood cells to the site of the infection. In turn, these cells emit a range of immune system chemicals such as kinins. These chemicals probably lead to the symptoms of the common cold by causing swelling and inflammation of the nasal membranes, leakage of proteins and fluid from capillaries and lymph vessels, and the increased production of mucus.
How colds are spread. Depending on the virus type, any or all of the following routes of transmission may be common:
Prevention. Handwashing is the simplest and most effective way to keep from getting rhinovirus colds. Not touching the nose or eyes is another. Individuals with colds should always sneeze or cough into a facial tissue, and promptly throw it away. Because rhinoviruses can survive up to three hours outside the nasal passages on inanimate objects and skin, cleaning environmental surfaces with a virus-killing disinfectant might help prevent spread of infection.
Treatment. Only symptomatic treatment is available for uncomplicated cases of the common cold: bed rest, plenty of fluids, gargling with warm salt water, applying petroleum jelly to a raw nose, and taking aspirin or acetaminophen to relieve headache or fever. Nonprescription cold remedies, including decongestants and cough suppressants, may relieve some cold symptoms but will not prevent, cure, or even shorten the duration of illness.
Antibiotics do not kill viruses. These prescription drugs should be used only for rare bacterial complications, such as sinusitis or ear infections, that can develop as secondary infections. The use of antibiotics “just in case” will not prevent secondary bacterial infections.
Does vitamin C have a role? Many people are convinced that taking large quantities of vitamin C will prevent colds or relieve symptoms. To test this theory, several large-scale, controlled studies involving children and adults have been conducted. To date, no conclusive data have shown that large doses of vitamin C prevent colds. The vitamin may reduce the severity or duration of symptoms, but there is no definitive evidence.