Common cold

The common cold is a mild viral infectious disease of the nose and throat, the upper respiratory system. Its symptoms are sneezing, sniffing, running/blocked nose (often these occur simultaneously, or one in each nostril), scratchy, sore, or phlegmy throat, coughing, headache, and a general feeling of unwellness; they typically last for 3 to 10 days. It is the most common of all diseases.

The common cold belongs to the upper respiratory tract infections. It is different from influenza, a more severe viral infection of the respiratory tract that shows the additional symptoms of rapidly rising fever, chills, and body and muscle aches.

Pathology

The common cold is caused by numerous viruses (mainly rhinoviruses, coronaviruses and also certain echoviruses and coxsackieviruses). Several hundred cold causing viruses have been described. These are transmitted from person to person by droplets resulting from coughs or sneezes. The droplets are either inhaled directly, or, more commonly, transmitted from hand to hand via handshakes or door knobs, and then introduced to the nasal passages when the hand touches the face.

The virus enters the cells of the lining of the nose and throat, and multiplies inside them. Ninety-five percent of people exposed to a cold virus become infected, although only 75% show symptoms. The symptoms start 1-2 days after infection. They are a result of the body's defense mechanisms: sneezes, runny nose and coughs to expel the invader, and inflammation to attract and activate immune cells. The virus takes advantage of sneezes and coughs to infect the next person just in time before it is killed by the immune system. A sufferer is most infectious within the first three days of the illness.

After a common cold, a sufferer develops immunity to the particular virus encountered. Because of the large number of different cold viruses however, this immunity is of little use.

The term "cold" is misleading, if "cold" refers to climatic temperature, as the temperature does not appear to play a role, nor are any other factors known which affect the probability of infection. It is perhaps the case that "cold" refers to a "cold condition," i.e., the hot, cold, dry and wet "conditions" described by the ancient Roman physician Galen. Colds are somewhat more common in winter since during that time of the year people spend more time indoors in close proximity of others and ventilation is less, increasing the infection risk. Some factors influence the severity of symptoms, for instance psychological stress and position in the menstrual cycle. Also, weak health in general, or other pre-existing conditions such as allergies can be aggravated due to infection.

Complications

Bacteria that are normally present in the respiratory tract can take advantage of the weakened immune system during a common cold and produce a co-infection. In children, a middle ear infection is a frequent complication; another common coinfections is bacterial sinusitis.

Prevention

The best way to avoid a cold is to avoid close contact with existing sufferers, to thoroughly wash hands regulary, and to avoid touching the face. Anti-bacterial soaps have no effect on the cold virus - it is the mechanical action of hand washing that removes the virus particles. In some countries, such as Japan, people with the common cold wear surgical masks out of courtesy.

Because of the large variety of viruses causing the common cold, vaccination is impractical.

Treatment

There is no cure for the common cold, i.e. there is no treatment that directly fights the viruses. Available treatments therefore focus on relieving the symptoms.

For many people, even without these remedies, colds are relatively minor inconveniences and they can go on with their daily activities with a little discomfort. This discomfort has to be weighed against the price and possible side effects of the remedies.

Common treatments include: analgesics such as NSAIDs or acetaminophen as well as localised versions targeting the throat (often delivered in lozenge form), nasal decongestants which reduce the inflammation in the nasal passages by constricting local blood vessels, cough suppressants (which work like a narcotic to suppress the cough reflex of the brain or by diluting the mucus in the lungs), and first generation anti-histamines such as brompheniramine, chlorpheniramine, and clemastine (which reduce mucus gland secretion and thus combat blocked/runny noses but have a sleep-inducing effect). Second generation anti-histamines do not have a useful effect on colds.

A warm and humid environment and drinking lots of fluids, especially hot liquids, alleviate symptoms somewhat. Common home remedies include camomile tea, chicken soup, nebulized medicinal mixtures, hot compresses, mustard plasters, hot toddies, vitamin C, and Echinacea, although despite several scientific trials there is no evidence that the final two have a beneficial effect. Hot beer is also recommended, and though it probably does little to fight the infection directly, at least it can help to a good night of relaxed sleep.

Zinc-containing preparates have been claimed to be effective in the treatment of cold infections. However, this has been attributed to a placebo effect related to the strong and unpleasant taste of zinc preparates. There was no effect in a proper double-blind experiment in which the test persons could not recognize the preparate by taste. Reference: Farr et al. (1987)

Antibiotics are ineffective against the common cold and all other viral infections. They are useful in treating any secondary bacterial infections that sometimes occur, but treatment with antibiotics before these coinfections develop is counterproductive, as it produces drug resistance.

Societal Impact

Common colds interfere with school attendance and can cause lost days on the job, resulting in considerable costs to the economy. In addition, much money is spent on over-the-counter and home remedies.

History

Colds were known in ancient Egypt; there were hieroglyphs for cough and for the common cold. The Greek Hippocrates gave a description of the disease in the 5th century BC.

In the 18th century, John Wesley wrote a book about curing diseases; it advised cold baths as prevention and stated that chilling causes the common cold. The work was widely reprinted in the 19th century. Another book by William Buchan in the 18th century also gave wet feet and clothes as the cause of the common cold.

The idea of microscopic infectious agents causing disease arose in the second half of the 19th century. Initially, bacteria were suspected to be the cause of the common cold, and vaccines were produced based on this theory; these were still prescribed in the 1950s.

Viruses had been described beginning with the 1890s: infectious agents so small that they would pass through all filters and could not be seen under a microscope. In 1914, Walter Kruse, a professor in Leipzig, showed that viruses caused the common cold: nose secretions of a cold sufferer were diluted, filtered, and introduced into the noses of volunteers, producing colds in about half of the cases. These findings were not widely accepted, until they were repeated in the 1920s by Alphonse Dochez, first in chimpanzees, and then in human volunteers using a double-blind setup.

Yet in 1932 a major textbook on the common cold by David Thomson still presented bacteria as the most likely cause. Among laymen, the common assumption that cold or wet clothes or feet cause the common cold persists to this day.

In Britain, the Common Cold Unit was set up by the civilian Medical Research Council in 1946. The unit worked with volunteers who were infected with various viruses. The rhinoviruses were discovered there. In the late 1950s, it was shown how to grow one these cold viruses in tissue culture (it would not grow in fertilized chicken eggs, the method used for many other viruses). In the 1970s, it was also shown that treatment with interferon during the incubation phase of rhinovirus infection protects somewhat against the disease, but no practical treatment could be developed. The unit was closed in 1989.

Beginning in the 1960s, Nobel Prize winner Linus Pauling heavily advocated the intake of large doses of Vitamin C to prevent infection. In 1970 he wrote the bestseller Vitamin C and the Common Cold. However, several subsequent studies have shown that the vitamin does not have a protective effect against the common cold.

See also

• upper respiratory tract infection
• Robitussin, a liquid common-cold relieving medicine.

External links

• Commoncold.org edited by MDs
• Merck Manual on Respiratory Viral Diseases: Common cold
• Common Cold syllabus from Infectious Diseases, Medical Microbiology, by Neal Chamberlain, PhD. Kirksville College of Osteopathic Medicine
• Common Cold Links to health information from MedlinePlus

Further reading

• Cold Wars - The Fight Against the Common Cold, by David Tyrrell, former Director of the Common Cold Unit, and Michael Fielder, ISBN 019263285X