Common cold
From Wikipedia, the free encyclopedia
| ICD-10 | J00.0 |
|---|---|
| ICD-9 | 460 |
| DiseasesDB | 31088 |
| MedlinePlus | 000678 |
| eMedicine | med/2339 |
| MeSH | D003139 |
Acute viral nasopharyngitis, often known as the common cold, is a viral infectious disease of the upper respiratory system (nose and throat).[1] Symptoms include sneezing, sniffling, runny nose, nasal congestion, scratchy, sore, or phlegmy throat, coughing, headache, and tiredness. In severe and rare cases, symptoms of conjunctivitis (red, itchy, or watery eyes) may also accompany a cold. Those affected may also feel achy. Colds typically last five to seven days, with residual coughing and/or catarrh lasting up to one to two weeks.[2] The common cold is the most common of all human diseases infecting adults at an average rate of 2–4 infections per year, and school-aged children as many as 12 times per year. Children and their parents or caretakers are at a higher risk, possibly due to the high population density of schools and because 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 be.
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[edit] Pathology
Most common colds are caused by infection by rhinovirus. Other viruses causing colds are coronavirus, human parainfluenza viruses, human respiratory syncytial virus, adenoviruses, enteroviruses, or metapneumovirus.[2][3]
[edit] Mechanism of infection
A cold virus can 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. The incubation period (time between becoming infected and developing symptoms) is one to three days.[4] The infectious period (time during which an infected person can infect others) begins about one day before symptoms begin, and continues for the first five days of the illness.[4] 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.
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).
[edit] Symptoms
Symptoms usually begin within 2 to 3 days after infection. The first indication of a cold is often a sore or scratchy throat. Other common symptoms are runny nose or congestion, sneezing and cough. These are sometimes accompanied by muscle aches, fatigue, and weakness. Colds rarely cause fever or headache, and never lead to extreme exhaustion. (These latter symptoms are more usual in influenza, and can differentiate the two infections.) The symptoms of a cold usually resolve after about one week, but can last up to 14 days, with a cough lasting longer than other symptoms. Symptoms may be more severe in infants and young children, and may include fever.[5][6][7]
Between one-third and one-half of all people exposed to a cold virus become infected;[8] 75% of the infected population show symptoms, which start 1–2 days after infection.
After a common cold, a sufferer develops immunity to the particular virus. This immunity offers only limited protection against the many other cold viruses. The person, therefore, can easily be infected by a different cold virus.
[edit] Complications
The weakened immune system caused by the common cold can lead to opportunistic coinfections or superinfections such as acute bronchitis, bronchiolitis, croup, pneumonia, sinusitis, otitis media, or strep throat. People with chronic lung diseases such as asthma and COPD are especially vulnerable. Colds may cause acute exacerbations of asthma, emphysema or chronic bronchitis.[1][2][3]
[edit] 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 mouth and face. Anti-bacterial soaps have no effect on the cold virus — it is the mechanical action of hand washing that removes the virus particles.[9]
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 of health care workers.[10] However, some alcohol-based hand sanitizers available to the public are ineffective in reducing bacterial count on the skin because the alcohol concentration is less than 60%.[11] As with hand washing with soap and water, alcohol gels provide no residual protection from re-infection.
The common cold is caused by a large variety of viruses, which mutate quite frequently during reproduction, resulting in constantly changing virus strains. Thus, successful immunization is highly improbable.
[edit] Treatment
As there is no medically proven and accepted medication directly targeting the causative agent, there is no cure for the common cold. Treatment is limited to symptomatic supportive options, maximizing the comfort of the patient, and limiting complications and harmful sequelae. The most reliable treatment is a combination of fluids and plenty of rest.
The common cold is self-limiting, and the host's immune system effectively deals with the infection. Within a few days, the body's humoral immune response begins producing specific antibodies that can prevent the virus from infecting cells. Additionally, as part of the cell-mediated immune response, leukocytes destroy the virus through phagocytosis and destroy infected cells to prevent further viral replication. In healthy, immunocompetent individuals, the common cold resolves in seven days on average.[1]
[edit] Palliative care
The National Institute of Allergy and Infectious Diseases suggests getting plenty of rest, drinking fluids to maintain hydration, gargling with warm salt water, using cough drops, throat sprays, or over-the-counter pain or cold medicines.[6] Saline nasal drops may help alleviate congestion.[12]
The American Lung Association recommends avoiding coffee, tea or cola drinks that contain caffeine and avoiding alcoholic beverages. Both caffeine and alcohol cause dehydration.[7]
[edit] Antibiotics
Antibiotics do not have any beneficial effect against the common cold. Their use in cases of common cold infection is ineffective and may contribute to antibiotic resistance of bacteria present in the patient's body.
[edit] Antivirals
There are no approved antiviral drugs for the common cold.
ViroPharma and Schering-Plough are developing an antiviral drug, pleconaril, that targets picornaviruses, the viruses that cause the majority of common colds. Pleconaril has been shown to be effective in an oral form.[13][14] Schering-Plough is developing an intra-nasal formulation that may have fewer adverse effects.[15]
[edit] Over-the-counter symptom medicines
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.
- analgesics such as aspirin or paracetamol, as well as localised versions targeting the throat (often delivered in lozenge form)
- nasal decongestants such as pseudoephedrine which reduce the inflammation in the nasal passages by constricting local blood vessels
- cough suppressants such as dextromethorphan which suppress the cough reflex.
- first-generation anti-histamines such as brompheniramine, chlorpheniramine, diphenhydramine 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.
[edit] Herbal remedies
Herbal teas, such as chamomile tea, or lemon or ginger root tisanes, may soothe some symptoms and comfort the patient.
Liquorice and garlic preparations have been suggested as treatments for the common cold, although efficacy is unproven.
Mustard plasters are an unproven homeopathic remedy for cold symptoms. Unfortunately, inhaling the active ingredient, mustard oil, can cause sneezing, coughing and asthma attacks. Skin contact for more than 30 minutes can cause blisters and ulcers.[16]
[edit] Echinacea
Echinacea, commonly called coneflowers, are plants with large showy heads of composite flowers . They are herbaceous, drought-tolerant perennial plants, native to North America, growing to 1 or 2 m in height. Echinacea is used in herbal preparations used to prevent or treat the common cold.
Although there have been scientific studies evaluating echinacea, its effectiveness has not been convincingly demonstrated. For example, 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.[17][18] Recent randomized, double-blind, placebo-controlled studies in adults have not shown a beneficial effect of echinacea on symptom severity or duration of the cold.[19][20] A structured review of 9 placebo controlled studies suggested that the effectiveness of echinacea in the treatment of colds has not been established.[21] Conversely, two recent meta-analyses of published medical articles concluded that there is some evidence that echinacea may reduce either the duration or severity of the common cold, but results are not fully consistent. However, there have been no large, randomized placebo-controlled clinical studies that definitively demonstrate either prophylaxis or therapeutic effects in adults.[22][23] A randomized, double-blind, placebo-controlled study in 407 children of ages ranging from 2 to 11 years showed that echinacea did not reduce the duration of the cold, or reduce the severity of the symptoms.[24] Most authoritative sources consider the effect of echinacea on the cold unproven.[2][6][7][25]
Reported adverse effects of echinacea include nausea, dizziness, dyspnea, rash, dermatitis, pruritis, and hepatotoxicity. These tend to be infrequent, mild and transient. Echinacea should not be taken with hepatotoxic drugs or immunosuppressants.[26] Forty-five percent of retail echinacea products failed quality testing by an independent consumer testing laboratory, due to either high lead levels, or low plant chemicals.[27]
[edit] Other
[edit] Vitamin C
A well known supporter of the theory that Vitamin C megadosage prevented infection was Nobel Prize winner Linus Pauling.[28] In 1970 he wrote the bestseller Vitamin C and the Common Cold.[29] A meta-analysis published in 2005 found that the lack of effect of prophylactic vitamin C supplementation on the incidence of common cold in normal populations throws doubt on the utility of this wide practice.[30]
A follow-up meta-analysis supported these conclusions:
Prophylactic use ...of vitamin C has no effect on common cold incidence ... [but] reduces the duration and severity of common cold symptoms slightly, although the magnitude of the effect was so small its clinical usefulness is doubtful. Therapeutic trials of high doses of vitamin C ... starting after the onset of symptoms, showed no consistent effect on either duration or severity of symptoms. ... More therapeutic trials are necessary to settle the question, especially in children who have not entered these trials.[31]
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 important, the plasma half life of high dose ascorbate above the baseline, controlled by renal resorption, is approximately 30 minutes,[32][33] 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.
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.[34]
The U.S. Institute of Medicine recommends a daily requirement of 45mg to 90mg of vitamin C for adults, up to 85mg for pregnant women and up to 120mg for nursing mothers,[35] while the European Commission Health and Consumer Protection DG recommends 40mg/d for adults (50mg/d and 60mg/d for pregnant women and nursing mothers, respectively).[36]
[edit] Zinc preparations
Zinc-containing lozenges were first claimed to be effective in the treatment of cold infections by Eby, Davis, and Halcomb.[37] 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.[38]
A 1997 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.[39] A 1999 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.[40] Another scientific review by George Eby in 2004, 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.[41] However, Eby and Halcomb failed to show any efficacy from zinc gluconate nasal sprays in 2006, and suggested why some throat lozenges are effective, while nasal application is not effective.[42]
There are concerns regarding the safety of long-term use of cold preparations in an estimated 25 million persons who are haemochromatosis heterozygotes.[43] Use of high doses of zinc for more than two weeks may cause copper depletion, which leads to anemia.[44] Other adverse events of high doses of zinc include nausea, vomiting gastrointestinal discomfort, headache and drowsiness.[44]
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[45] 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.[3]
- See also: Zinc gluconate
[edit] 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 its effectiveness has not been proven.[citations needed]
[edit] Steam inhalation
Many people believe that steam inhalation reduces symptoms of the cold.[46] In some parts of the world this remedy (Italian: suffumigio) has been used for centuries and is commonly considered very effective.[citations needed]
However, a double-blind, placebo-controlled, randomized study found no affect of steam inhalation on cold symptoms.[47] A scientific review of medical literature concluded that "there is insufficient evidence to support the use of steam inhalation as a treatment."[48] There have been reports of children being badly burned when using steam inhalation to alleviate cold symptoms leading to the recommendation to "...start discouraging patients from using this form of home remedy, as there appears to be no significant benefit from steam inhalation."[49]
[edit] Chicken soup
In the twelfth century, Moses Maimonides wrote, "Chicken soup...is recommended as an excellent food as well as medication."[50] Since then, there have been numerous reports that chicken soup alleviates the symptoms of the common cold. Even usually staid medical journals have published tongue-in-cheek humorous articles on the alleged medicinal properties of chicken soup.[51][52][53] However, the efficacy of chicken soup has not been studied in any rigorous clinical trials. Nevertheless, hot chicken soup is nutritious, easy to eat, aids in rehydration, and provides a temporary feeling of relief.
[edit] 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 large sum of money is spent on over-the-counter drugs and home remedies.
Many companies offer a number of paid sick days per year to avoid errors during work and transmission to co-workers. In many countries this is mandated by law.
University of Michigan researcher Dr. A. Mark Fendrick published a 2003 study on effects of the common cold in the United States. 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. In the UK, £67,692,708.08 were lost in the cause of workdays lost due to rhinovirus.[citation needed]
Recent UK studies have shown that men take longer to recover from the common colds than women, leading to the introduction of the term Man Flu. While such so-called Man Flu is no different than the common cold, the differences in symptoms and recovery between males and females has puzzled many researchers.[citation needed] The term Man Flu is also sometimes used when a person is exaggerating their cold for personal reasons, i.e to allow them more time off work/school.
[edit] History
Colds have existed since ancient times, being known in ancient Egypt, where 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 against cold baths, stating 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 that microscopic infectious agents cause disease only 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 in 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 the United Kingdom, 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, as 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.[54]
[edit] "Cold" as a misnomer
Originally, the term "cold" may have referred to a "cold condition" such as the hot, cold, dry, and wet "conditions" described by the ancient Anatolian physician Galen, but the climate is only an enabler and not the cause. Colds are somewhat more common in winter, and cold climate may affect transmission by causing people to stay indoors where ventilation is reduced and proximity to infected persons is increased, 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.[citations needed]
Infection with a cold virus affects thermogenesis. This makes people associate post-infection shivering with situations in which they were exposed to cold that intensifies shivering (e.g. wet hair, draft, long wait on a bus stop, etc.). This association helps propagate the myth.[citations needed]
If cold weather were directly linked to the spread of the common cold, then it could possibly be demonstrated 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 done in the 1960s found no significant increase in infection rates in people who live in colder climates.[55] [56] [57]
It is not known conclusively 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.[citations needed]
In a widely-publicized, but flawed, experiment, researchers at the Common Cold Centre at the Cardiff University attempted to demonstrate that cold temperatures can lead to a greater susceptibility to viral infection.[58] In the experiment, 29% of a group of 90 people who sat with their feet in ice-cold water for 20 minutes a day for five days developed cold symptoms during the five days, while 9% of a control group of 90 people who were not similarly exposed developed symptoms. However, when interviewed on NPR, Dr. Ronald Turner (University of Virginia) pointed out a flaw in the study: the experiment only recorded symptoms and not actual viral infections.[59]