Common cold

For a villain character in Codename: Kids Next Door, see Common Cold (Codename: Kids Next Door)

Common cold
Specialty	Family medicine, infectious diseases, otorhinolaryngology

The acute nasopharyngitis, often known as the common cold is a mild viral infectious disease of the nose and throat; the upper respiratory system. Symptoms include sneezing, sniffling, nasal congestion; scratchy, sore, or phlegmy throat; coughing; headache; and tiredness. Colds typically last three to five days, with residual coughing lasting up to three weeks. As its name suggests, 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 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 rarely 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 also can 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.

"Cold" as misnomer

The term "cold", as it relates to climatic temperature is somewhat misleading. (This is not limited to English; many other European languages contain the root word for "cold" in their words for the common cold.) 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 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 the objects that they touch, as well as by keeping their immune system in top form by getting enough sleep, reducing stress, eating nutritious foods, and avoiding excess alcohol consumption. However, researchers at the Common Cold Centre at the University of Cardiff [1] recently demonstrated that cold temperatures can lead to a greater susceptibility to viral infection. They showed that a group of people who sat with their feet in cold water for 20 minutes a day for a week had a 1 in 3 chance of developing cold symptoms during that week, while a control group who sat with their feet in an empty bowl had a 1 in 10 chance. It is thought this may be due to cold temperatures reducing blood circulation needed to carry white blood cells to the area 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 Anatolian 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 natural ventilation is generally less prevalent in cold weather, which increases 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. Generally a cold starts with a sore throat only without any blockage. From then onwards the symptoms 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 defeated 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 also can 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 partially dissipate. Doing so will reduce the pressure that would otherwise drive fluid into the ears or sinuses.

Prevention

The best way to avoid a cold is to avoid close contact with existing sufferers, to wash hands thoroughly and 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. Tobacco smoking has also been linked with the weakening of the immune system; non-smokers are known on average to take fewer days off sick than the smoking population. Smokers on average take 25% more sick days a year.

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.

ViroPharma Incorporated and Schering-Plough have been developing an anti-viral drug that targets picornaviruses, that cause the majority of common colds. Pleconaril has been shown to be effective in an oral form, but there were safety problems with that formulation. Schering-Plough is developing an intra-nasal formulation that may overcome some of those safety issues. However it may not be until 2008 or 2009 that the drug is on the market and it is unlikely that benefit will be more than one day.

Available treatments do not treat the viral infection, but 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 aspirin or acetaminophen / paracetamol, 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, lemon or ginger root tisanes and chicken soup (which probably work by soothing the irritated respiratory passages with their steam), 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. A peer-reveiwed clinical study published in the New England Journal of Medicine concluded that ...extracts of E. angustifolia root, either alone or in combination, do not have clinically significant effects on rhinovirus infection or on the clinical illness that results from it. [2]

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 provide a good night of relaxed sleep. However, alcohol dehydrates the body which is counterproductive; also cold medicine (aspirin, acetaminophen / paracetamol, ibuprofen, etc) should never be taken along with alcohol.

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.

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.^[3]

Zinc Preparations

Main article: Zinc gluconate

Zinc-containing preparations have been claimed to be effective in the treatment of cold infections.^[4] There have been a number of clinical studies of the efficacy of zinc, some of which have shown an effect and some of which have shown no effect.^[5]

A meta-analysis of six clinical studies concluded that Despite numerous randomized trials, the evidence for effectiveness of zinc salts lozenges in reducing the duration of common colds is still lacking.^[6] A scientific review of published data concluded: Overall, the results suggest that treatment with zinc lozenges did not reduce the duration of cold symptoms. Evidence of the effects of zinc lozenges for treating the common cold is inconclusive. Given the potential for treatment to produce side effects, the use of zinc lozenges to treat cold symptoms deserves further study.^[7] Another scientific review, one that considered the solution chemistry of all zinc lozenge formulations tested from 1984 through 2004, showed a statistically significant dose response when the amount of ionic zinc, rather than total zinc, was considered.^[8]

There are concerns regarding the safety of long-term use of cold preparations in an estimated 25 million persons who are haemochromatosis heterozygotes.^[9] Another concern with use of very high-dose zinc for more than two weeks is copper depletion, which leads to anemia.

Although widely available and advertized in the United States, the safety and efficacy of zinc preparations have not been evaluated or approved by the Food and Drug Administration, and they are not likely to have any utility against colds due to removal of ionic zinc through additive food acids (citric acid, ascorbic acid and glycine). Consequently, a "cure for the common cold", using zinc acetate lozenges without additive food acids ^[10], is not available due to marketing rather than scientific considerations.

In the United Kingdom, the National Health Service includes zinc lozenges in a list of not recommended treatments.[11]

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.

University of Michigan researcher Dr. A. Mark Fendrick published 2003 study on effects of the common cold: The study found that the common cold leads to more than 100 million physician visits annually at a conservative cost estimate of $7.7 billion per year. More than one-third of patients who saw a doctor received an antibiotic prescription, which Fendrick says not only contributes to unnecessary costs, but also has implications for antibiotic resistance from overuse of such drugs.

The study found that Americans spend $2.9 billion on over-the-counter drugs and another $400 million on prescription medicines for symptomatic relief. Additionally, cold sufferers spend $1.1 billion annually on an estimated 41 million antibiotic prescriptions, even though the drugs have no effect on a viral illness.

The study reports that an estimated 189 million school days are missed annually due to a cold. As a result, parents missed 126 million workdays to stay home to care for their children. When added to the workdays missed by employees suffering from a cold, the total economic impact of cold-related work loss exceeds $20 billion.

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, Germany, 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.

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, just two years after their showing benefit of zinc gluconate lozenges in the prophylaxis and treatment of rhinovirus colds. (reference: [12])

See also

• Upper respiratory tract infection

Notes

• ^ Douglas RM, Hemilä H. Vitamin C for Preventing and Treating the Common Cold. PLoS Med 2005;2(6):e168.
• ^ Eby G.A., Davis D.R., and Halcomb, W.W. 1984 Reduction in duration of common colds by zinc gluconate lozenges in a double-blind study Antimicrob Agents Chemother. 1984 January; 25(1): 20-24
• ^ U.S. Patent 5,409,905, Cure for Common Cold, G.A. Eby, 1995
• ^ Hulisz, D.T. Zinc and the Common Cold: What Pharmacists Need to Know (accessed 2005-01-31)
• ^ Marshall I. 1999. Zinc for the common cold. The Cochrane Database of Systematic Reviews (accessed 2005-01-31)
• ^ Barton, JC and Bertoli LF. 1997. Zinc Gluconate Lozenges for Treating the Common Cold. Annals of Internal Medicine 126:738.
• ^ Jackson, J.L., Peterson, C. and Lesho, E. (1997) A meta-analysis of zinc salts lozenges and the common cold. Archives of Internal Medicine 157(20), 2373-2376
• ^ Eby GA. 2004. Zinc lozenges: cold cure or candy? Solution chemistry determinations. Biosci Rep. 24:23-39.

External links

• US Food and Drug Administration, May 2000. What to Do for Colds and Flu
• 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
• Acute cooling of the feet and the onset of common cold symptoms Johnson and Eccles Fam. Pract..2005; 0: 721
• Common Cold Centre at Cardiff University

Further reading

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