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 last between 3 to 10 days, with residual coughing lasting up to 3 weeks. It is the most common of all diseases, infecting subjects at an average of slightly over one infection per year with greater than 3 infections per year 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.
| Contents |
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. These 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, and rapidly multiplies inside them. Nasopharynx being the area between the nose and throat is the central area infected. The mouth is not a major point of entry and virus transmission does not usually occur with kissing or swallowing, whereas the nose and the eye, through its nasolacrymal duct drainage into the nasopharynx are the major entrypoints. The specific localization in the nasopharynx and avoidance of the throat may be due to the low temperature here as well as the 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 and its concentration can be affected by various things including allergic rhinitis and some other irritants including rhinovirus itself and has been a major focal point in drug research into treatment. 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 hours - with part of the water droplets evaporating and leaving much smaller and invisible "droplet nuclei" in the air. Droplets by 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 symptomless subjects exibit virus 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. Because of the large number of different cold viruses however, this immunity is of limited use and a person can easily be infected by another cold virus to start the process all over again.
The term "cold" is misleading, if "cold" refers to climatic temperature, as the aetiology is viral. 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. Whether cold, or 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 has not yet been thoroughly tested and is not known. A person can best avoid colds by avoiding those who are ill and objects 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 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. 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, vitamin C, and Echinacea. Although there have been scientific studies done on echinacea its effectiveness has not been demonstrated, whilst there is some evidence that Vitamin C will reduce the length of the infection (although it will not, as commonly believed, prevent contracting a cold in the first place). 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.
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) (http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=174900&action=stream&blobtype=pdf), while other studies claim that zinc lozenges are effective in reducing the duration and severity of common colds. (Reference: [1] (http://coldcure.com/html/prasad.pdf))
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. References:
- Belongia EA, Berg R, Liu K. A randomized trial of zinc nasal spray for the treatment of upper respiratory illness in adults.
- American Journal of Medicine 2001, p.111, 103–108. Hirt M, Nobel S, Barron E. Zinc nasal gel for the treatment of common cold symptoms: a double-blind, placebo-controlled trial.
- Ear Nose Throat Journal 2000, p.79,778–781. Mossad SB. Effect of zincum gluconicum nasal gel on the duration and symptom severity of the common cold in otherwise healthy adults.
- QJM. 2003;96:35–43. Zicam (http://www.zicam.com), an over the counter (OTC) product of GumTech International, has developed a patent-pending solution in which zincum gluconicum nasal gel has been utilized to decrease symptoms and shorten the duration of the common cold up to 85%.
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 (by Linus Pauling, among others) suggested that large doses of Vitamin C could both prevent and reduce the effects of the common cold. However, the Australian Medical Association has experimented and concluded that large maintenance doses of Vitamin C do not lower the incidence of colds and has conflicting evidence as to whether or not Vitamin C will shorten the duration of symptoms of any colds that occur.[2] (http://www.ama.com.au/web.nsf/doc/SHED-5EXHNL)
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.
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.
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
External links
- Commoncold.org (http://www.commoncold.org/) edited by MDs
- Merck Manual on Respiratory Viral Diseases: Common cold (http://www.merck.com/pubs/mmanual/section13/chapter162/162b.htm)
- Common Cold syllabus (http://www.kcom.edu/faculty/chamberlain/Website/lectures/lecture/uri.htm) from Infectious Diseases, Medical Microbiology, by Neal Chamberlain, PhD. Kirksville College of Osteopathic Medicine
- Common Cold (http://www.nlm.nih.gov/medlineplus/commoncold.html) Links to health information from MedlinePlus
- Do I have a Cold or the Flu? (http://www.consumerreports.org/main/content/display_report.jsp?FOLDER%3C%3Efolder_id=377601&bmUID=1101139924451) from ConsumerReports.org
- "Falling ill to a chill" (http://www.findarticles.com/p/articles/mi_qn4196/is_200303/ai_n10850727) (Milwaukee Journal Sentinel, 17 Mar 2003)
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
es:Resfrío común it:Raffreddore ja:風邪 nl:verkoudheid de:Erkältung sv:Förkylning zh:感冒