Common cold

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

Common cold
Specialty	Family medicine, infectious diseases, otorhinolaryngology

Acute nasopharyngitis, often known as the common cold, is a mild viral infectious disease of the upper respiratory system (nose and throat). 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.

File:What happens after a cold.jpg

Common cold patient

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 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.

Transmission

The viruses are transmitted from person to person by droplets 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 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 droplet nuclei 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.

Mechanism of Infection

The virus enters the cells of the lining of the nasopharynx (the area between the nose and throat), and rapidly multiplies. The major entry point is normally the nose, but can also be the eyes (in this case drainage into the nasopharynx would occur through the Nasolacrimal duct). The mouth is not a major point of entry and transmission does not usually occur with kissing or swallowing.

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.

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, without any respiratory 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.

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 offers limited protection. A person therefore can be easily infected by another cold virus, starting 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 coinfection. 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. 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—no medically-proven treatment that directly fights the virus.

Only the body's immune system can effectively destroy the invader, a process which generally takes about 7 days in healthy individuals. 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. Since the duration of infection is on the order of a few days to one week, even a proven cure could only reduce the duration by a few days. That said, there are both experimental pharmaceutical and unproven natural remedies.

Antibiotics

Antibiotics are not a cold remedy. Antibiotics do not treat viral infections, and thus are ineffective against the common cold. Treatment of colds with antibiotics can be counterproductive, as it can promote the production of drug resistant bacteria, and can even promote infections by killing off normal bodily flora.

Echinacea

Although there have been scientific studies done on echinacea, its effectiveness has not been demonstrated. A peer-reviewed 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. [1]

Pharmaceuticals

ViroPharma Incorporated and Schering-Plough have been developing an anti-viral drug that targets picornaviruses, the viruses that cause the majority of common colds. Pleconaril has been shown to be effective in an oral form, but significant side effects make current formulations unsafe. Schering-Plough is developing an intra-nasal formulation that may overcome some of these safety issues. However, it may not be until 2008 or 2009 that the drug is on the market.

Interferons

Interferons, natural proteins produced by the cells of the immune system, can be administered intranasally in low doses. In Eastern Europe, Russia, and Japan this is used as a method to prevent and treat viral respiratory diseases such as cold and flu, though most western doctors dispute the effectiveness of this treatment. Work is currently being done on interferon lozenges as an alternative method of delivery.

Vitamin C

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 well known supporter of this theory was Nobel Prize winner Linus Pauling, who publicly advocated the intake of large doses of Vitamin C to prevent infection. In 1970 he wrote the bestseller Vitamin C and the Common Cold. A meta-analysis published in 2005 found that vitamin C reduced the incidence of colds by 50% in six trials with physically stressed participants, but that 200^{+mg daily had no effect on the incidence of colds in ordinary people. Regular vitamin C supplementation shortened the duration of colds in children by 14% and in adults by 8%. Findings from therapeutic trials have been conflicting, yet it is worth noting that none of the therapeutic trials carried out so far have examined the effect of vitamin C on children, although the regular supplementation trials have shown a substantially greater effect on episode duration in children.}

The Vitamin C Foundation recommends an initial usage of up to 8 grams of vitamin C every 20-30 minutes in order to show an effect on the symptoms of a cold infection that is in progress. Most of the studies showing little or no effect employ doses of ascorbate such as 100 mg to 500 mg per day, considered "small" by vitamin C advocates. Equally importantly, the plasma half life of high dose ascorbate is approximately 30 minutes, which implies that most high dose studies have been methodologically defective and would be expected to show a minimum benefit. Clinical studies of divided dose supplementation, predicted on pharmacological grounds to be effective, have only rarely been reported in the literature. Essentially all the claims for high dose vitamin C have been neither validated nor invalidated, and the clinical effectiveness of large and frequent doses of vitamin C is an open scientific question.

Because vitamin C is metabolized to oxalic acid in the body, some scientists have long speculated that high doses may contribute to the development of kidney stones. Experiments have proven inconclusive and direct cause and effect have not been shown, but further study seems warranted.

Zinc Preparations

Main article: Zinc gluconate

Zinc-containing preparations have been claimed to be effective in the treatment of cold infections. 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.

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. 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. 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.

There are concerns regarding the safety of long-term use of cold preparations in an estimated 25 million persons who are haemochromatosis heterozygotes. 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 advertised 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 , 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.[2]

Zicam Cold Remedy is a non-drip nasal gel containing Zincum Gluconicum to "Reduce the duration; Reduce the severity of the common cold." Research on the nasal gel has shown that if taken within 24 hours of the initial cold symptoms it can shorten a cold to just five days.[3] The nasal gel works best when taken within 24 hours of the first symptoms of a cold, and has not been proven to be effective if taken outside this window. [4] A $75,000,000 lawsuit against the company that makes Zicam Cold Remedy filed by people who claimed that the nasal gel caused them to lose their sense of smell[5] was settled out of court for $12,000,000 but the company did not admit fault.[6]

Non-Cure Treatments

Though cures are unproven, there are a number of effective treatments which, rather than treat the viral infection, focus on relieving the symptoms. For some people, 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, though not 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 such as phenylephrine HCI 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, can alleviate symptoms somewhat. Common home remedies include chamomile, 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. Eating 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.

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, a lot of money is spent on over-the-counter and home remedies.

Arguably the most common communicable 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.

Most companies offer a number of paid sick days per year to avoid errors during work and transmission to co-workers.

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 representing the cough and the common cold. The Greek physician Hippocrates gave a description of the disease in the 5th century BC. The common cold was also known among 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 double-blind setup. Nevertheless, 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 rhinovirus was discovered there. In the late 1950s, researchers were able to grow one of these cold viruses in a tissue culture (it would not grow in fertilized chicken eggs, the method used for many other viruses). In the 1970s, the CCU demonstrated 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 it demonstrated the benefit of zinc gluconate lozenges in the prophylaxis and treatment of rhinovirus colds. [7]

"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 [8] 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 were not exposed to the chill 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.

Moreover, if cold weather is directly linked to the spread of the common cold, then it would be easy to prove by comparing the infection rates of people who live in colder climates (such as Iceland or Greenland) with people who live in warmer climates (such as countries close to the equator). Studies have shown no significant increase in infection rates in people who live in colder climates.[9]

In fiction

The common cold famously defeated the aliens in H. G. Wells' The War of the Worlds.

See also

• Upper respiratory tract infection

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
• Basic Common Cold Information
• 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
• Infection Protection: Pandemic
• Infection Protection: How to Fight the Germs That Make You Sick
• Common Cold Home Remedy

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