Common cold

For the Codename: Kids Next Door character with this name, see Common Cold.

The common cold is a mild viral infectious disease of the nose and throat; the upper respiratory system. Symptoms include sneezing, sniffling, running/blocked nose (often these occur simultaneously, or one in each nostril); scratchy, sore, or phlegmy throat; coughing; headache; and tiredness. Colds typically last between three to five days, with residual coughing lasting up to three weeks. As its name implies, it is the most common of all human diseases, infecting subjects at an average rate of slightly over one infection per year per person. Infection rates greater than three infections per year per person are not uncommon in some populations. Children and their caretakers are at a higher risk, probably due to the high population density of schools and the fact that transmission to family members or caretakers is highly efficient.

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. While the common cold itself is hardly life threatening, its complications, such as pneumonia, can very well be.

Pathology

The common cold is caused by numerous viruses (mainly rhinoviruses, coronaviruses and also certain echoviruses, paramyxoviruses and coxsackieviruses) infecting the upper respiratory system. Several hundred cold-causing viruses have been described, and a virus can mutate to survive, ensuring that any cure is still a long way off. The viruses are transmitted from person to person by droplets resulting from coughs or sneezes. The droplets or droplet nuclei are either inhaled directly, or, transmitted from hand to hand via handshakes or objects such as door knobs, and then introduced to the nasal passages when the hand touches the nose, or eyes.

The virus enters the cells of the lining of the nasopharynx (the area between the nose and throat), and rapidly multiplies. The major entry points are the nose and eyes, through the nasolacrymal duct drainage into the nasopharynx. The mouth is not a major point of entry and transmission does not usually occur with kissing or swallowing. The nasopharynx is the central area infected. The reasons that the virus concentrates in the nasopharynx rather than the throat may be the low temperature and high concentration of cells with receptors needed by the virus.

The virus enters the cell by binding to ICAM-1 receptors in these cells. The presence of ICAM-1 affects whether a cell will be infected. Its concentration can also be affected by various other factors, including allergic rhinitis and some other irritants including rhinoviruses themselves. ICAM-1 has been a major focal point in drug research into cold treatments.

Some factors, such as psychological stress and a woman's position in the menstrual cycle, influence the severity of symptoms. Also, generally poor health or other pre-existing conditions such as allergies can be aggravated by a cold infection.

"Cold" as misnomer

The term "cold" (as it relates to climatic temperature) is somewhat misleading. Climate may affect transmission by some means, such as by causing people to stay indoors and increasing the proximity to infected persons, but the cause of the infection remains primarily viral. Some allergies, bacterial respiratory infections, and even climate changes can also cause common-cold-like symptoms that can last for days. It is not definitely known whether cold weather or a humid climate can affect transmission by other means, such as by affecting the immune system, or ICAM-1 receptor concentration, or simply increasing the amount and frequency of nasal secretions and frequency of hand to face contact. A person can best avoid colds by avoiding those who are ill and objects that they touch, as well as keeping their immune system in top form by getting enough sleep, reducing stress, eating nutritious foods, and avoiding excess alcohol consumption.

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 to others, and ventilation is less efficient, increasing the infection risk.

Symptoms

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 before it is killed by the body's immune system. Sneezes expel a significantly larger concentration of virus "cloud" than coughing. The "cloud" is partly invisible and falls at a rate slow enough to last for hours - with part of the water droplets evaporating and leaving much smaller and invisible "droplet nuclei" in the air. Droplets from turbulent sneezing or coughing or hand contact can also last for hours on surfaces, although less virus can be recovered from porous surfaces such as wood or paper towel than non-porous surfaces such as a metal bar. A sufferer is most infectious within the first three days of the illness. Symptoms, however, are not necessary for viral shedding or transmission, as a percentage of asymptomatic subjects exhibit viruses in nasal swabs, likely controlling the virus at concentrations too low for them to have symptoms.

After a common cold, a sufferer develops immunity to the particular virus encountered. However, because of the large number of different cold viruses, this immunity is of limited use. A person can therefore easily be infected by another cold virus to start the process all over again.

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. Middle ear infection (in children) and bacterial sinusitis are common coinfections. A possible explanation for these coinfections is that strong blowing of the nose drives nasal fluids into those areas. The best way to blow the nose is keeping both nasal openings open when blowing and wiping rather than fully covering them, permitting pressure to dissipate partly here. This will reduce the pressure which could drive fluid into the ears or sinuses where it can cause infection.

Prevention

The best way to avoid a cold is to avoid close contact with existing sufferers, to thoroughly wash hands regularly, 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 2002, the Centers for Disease Control and Prevention recommended alcohol based hand gels as an effective method for reducing infectious viruses on the hands. However, as with standard handwashing, alcohol gels provide no residual protection from re-infection. In some countries, such as China and Japan, people with the common cold wear surgical masks out of courtesy to protect others.

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 virus. Only the body's immune system can effectively destroy the invader. A cold may be composed of several million viral particles, and typically within a few days the body begins mass producing a better tailored antibody that can prevent the virus from infecting cells, as well as white blood cells which destroy the virus through phagocytosis and destroy infected cells to prevent further viral replication. Furthermore the duration of infection is on the order of a few days to one week so at most a "cure" could hope to reduce the duration by only a few days.

Available treatments therefore focus on relieving the symptoms.

For some people, even without these remedies, colds are relatively minor inconveniences and they can go on with their daily activities with tolerable discomfort. This discomfort has to be weighed against the price and possible side effects of the remedies, and the possibility, not yet scientifically proven, that by suppressing responses evolved to fight the cold, the symptom suppressants may prolong the illness.

Common treatments include: analgesics such as NSAIDs such as aspirin 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 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 also may make the user drowsy). 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, Licorice and Echinacea. Although there have been scientific studies done on echinacea its effectiveness has not been demonstrated. Eating very spicy food can help alleviate congestion, although it may also irritate the already-tender throat. Coffee, or its active component, caffeine, has also been shown to improve mood and mental performance during rhinovirus infection. 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. Too much alcohol dehydrates the body, which is counterproductive.

Publications in the 1960s and 1970s suggested that large doses of Vitamin C could both prevent and reduce the effects of the common cold. A particularly vociferous proponent of this theory was Nobel Prize winner Linus Pauling, who 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, most physicians feel that large maintenance doses of Vitamin C do not lower the incidence of colds, and evidence has been conflicting as to whether or not vitamin C will shorten the duration of symptoms of any colds that occur. A meta-analysis published in 2005 found no support that vitamin C is of any benefit in the common cold^[1].

Zinc-containing preparates have been claimed to be effective in the treatment of cold infections. Some studies have attributed this to a placebo effect related to the strong and unpleasant taste of zinc preparates (Reference: Farr et al. (1987), while other studies claim that zinc lozenges are effective in reducing the duration and severity of common colds. (Reference: [2])

Advocates for Zinc nasal sprays, however, claim clinical proof that they work. The trick seems to be threefold. One, the treatment has to be a nasal spray. Two, treatment should be started at the first sign of a cold before it has the chance to get established. Three, the type of zinc must be zinc gluconate usually labelled as zincum gluconicum. There have been several hundred lawsuits filed alleging that zinc nasal sprays may cause permanent damage to the sense of smell.

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, and can even promote infections by killing off normal bodily flora.

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.

Arguably the most common disorder that humans can be afflicted with, the cold is considered something of a common cultural point of reference. Thus, catching a cold is often used as a plot device in various stories, movies, and television series.

Some companies have begun to offer a number of paid sick days per year to avoid errors during work and transmission to coworkers.

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. The common cold was also known in the ancient American Indian Aztec and Maya civilizations. A mixture of chili pepper, honey, and tobacco was one common Aztec treatment for colds.

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 could 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 proper 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 of 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.

See also

• Upper respiratory tract infection

Note

• ^ Douglas RM, Hemilä H. Vitamin C for Preventing and Treating the Common Cold. PLoS Med 2005;2(6):e168.

External links

• Commoncold.org edited by MDs
• Common Cold Links to health information from MedlinePlus
• Common Cold syllabus from Infectious Diseases, Medical Microbiology, by Neal Chamberlain, PhD. Kirksville College of Osteopathic Medicine
• Do I have a Cold or the Flu? from ConsumerReports.org
• "Falling ill to a chill" (Milwaukee Journal Sentinel, 17 Mar 2003)
• Merck Manual on Respiratory Viral Diseases: Common cold
• The first common cold experiments (1946) with film clip

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