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The common cold (viral upper respiratory tract infection (VURI), acute viral nasopharyngitis, acute viral rhinopharyngitis, acute coryza, or a cold) is a contagious, viral infectious disease of the upper respiratory system, primarily caused by rhinoviruses, (picornaviruses) or coronaviruses. It is the most common infectious disease in humans; there is no known cure, but it is very rarely fatal.

Collectively, colds, influenza, and other infections with similar symptoms are included in the diagnosis of influenza-like illness. Often, influenza and the common cold are mistaken for each other, even by professional healthcare workers, but most of the recommended home treatments (drinking plenty of warm fluids, keeping warm, etc.) are similar if not the same. The symptoms of influenza often include a fever and are more severe than the cold.

Symptoms

Common symptoms are cough, sore throat, runny nose, nasal congestion, and sneezing; sometimes accompanied by 'pink eye', muscle aches, fatigue, malaise, headaches, muscle weakness, uncontrollable shivering, loss of appetite, and rarely extreme exhaustion. Fever is more commonly a symptom of influenza, another viral upper respiratory tract infection (URTI) whose symptoms broadly overlap with the cold but are more severe. Symptoms may be more severe in infants and young children (due to their immune system not being fully developed) as well as the elderly (due to their immune system often being weakened).

Those suffering from colds often report a sensation of chilliness even though the cold is not generally accompanied by fever, and although chills are generally associated with fever, the sensation may not always be caused by actual fever. In one study, 60% of those suffering from a sore throat and upper respiratory tract infection reported headaches, often due to nasal congestion. The symptoms of a cold usually resolve after about one week; however, it is not rare that symptoms last up to three weeks.

Complications

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.

Causes

Viruses

The common cold is most often caused by infection with one of the 99 known serotypes of rhinovirus, a type of picornavirus. Around 30-50% of colds are caused by rhinoviruses. Other viruses causing colds are coronavirus (causing 10-15%), human parainfluenza viruses, human respiratory syncytial virus, adenoviruses, enteroviruses, or metapneumovirus. 5-15% are caused by influenza viruses. In total over 200 serologically different viral types cause colds. Coronaviruses are particularly implicated in adult colds. Of over 30 coronaviruses, 3 or 4 cause infections in humans, but they are difficult to grow in the laboratory and their significance is thus less well-understood. Due to the many different types of viruses and their tendency for continuous mutation, it is impossible to gain complete immunity to the common cold.

Sleep

Lack of sleep has been associated with the common cold. Those who sleep fewer than 7 hours per night were three times more likely to develop an infection when exposed to a rhinovirus when compared to those who sleep more than 8 hours per night.

Vitamin D

A 2009 study found that low blood serum levels of vitamin D were associated with increased rates of the common cold.

Cold weather

An ancient belief still common today claims that a cold can be "caught" by prolonged exposure to cold weather such as rain or winter conditions, which is where the disease got its name. Although common colds are seasonal, with more occurring during winter, experiments so far have failed to produce evidence that short-term exposure to cold weather or direct chilling increases susceptibility to infection, implying that the seasonal variation is instead due to a change in behaviors such as increased time spent indoors at close proximity to others.

With respect to the causation of cold-like symptoms, researchers at the Common Cold Centre at Cardiff Universitymarker conducted a study to "test the hypothesis that acute cooling of the feet causes the onset of common cold symptoms." The study measured the subjects' self-reported cold symptoms, and belief they had a cold, but not whether an actual respiratory infection developed. It found that a significantly greater number of those subjects chilled developed cold symptoms 4 or 5 days after the chilling. It concludes that the onset of common cold symptoms can be caused by acute chilling of the feet. Some possible explanations were suggested for the symptoms, such as placebo, or constriction of blood vessels of the nasal passages which might lead to reduced immunity, however "further studies are needed to determine the relationship of symptom generation to any respiratory infection."

Another possibility which remains to be explored involves the role that proteins of the complement system play in the prevention of a sustained infection. Decreased temperature may result in a drop in tissue permeability and, as a result, may lead to reduced plasma leakage. Among the many proteins suspended in plasma are complement proteins (e.g. C3) which serve to disable, destroy, or tag for destruction foreign particulate (in this case viral capsids). Thus, sustained exposure to cold may inhibit the effectiveness of the complement system and allow the virus a better chance of establishing a state of infection.

ICAM-1, the receptor that Rhinovirus binds to in order to infect cells, is known to increase in number and receptiveness in response to many irritants, including dust and pollen. That a cold climate in combination with varying degrees of humidity can act as a similar "irritant" needs to be investigated.

Pathophysiology



The common cold virus is transmitted mainly from contact with the saliva or nasal secretions of an infected person, either directly, in aerosol form generated by coughing and sneezing, or from contaminated surfaces.

Symptoms are not necessary for viral shedding or transmission, as a percentage of asymptomatic subjects exhibit viruses in nasal swabs. It is generally not possible to identify the virus type through symptoms, although influenza can be distinguished by its sudden onset, fever, and cough.

The major entry point for the virus is normally the nose, but can also be the eyes (in this case drainage into the nasopharynx would occur through the nasolacrimal duct). From there, it is transported to the back of the nose and the adenoid area. The virus then attaches to a receptor, ICAM-1, which is located on the surface of cells of the lining of the nasopharynx. The receptor fits into a docking port on the surface of the virus. Large amounts of virus receptor are present on cells of the adenoid. After attachment to the receptor, virus is taken into the cell, where it starts an infection. Rhinovirus colds do not generally cause damage to the nasal epithelium. Macrophages trigger the production of cytokines, which in combination with mediators cause the symptoms. Cytokines cause the systemic effects. The mediator bradykinin plays a major role in causing the local symptoms such as sore throat and nasal irritation.

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.

Incubation period and progression of disease

The upper respiratory viral replication cycle begins 8 to 12 hours after initial infection. Symptoms usually begin 2 to 5 days after initial infection but occasionally occur in as little as 10 hours after. Symptoms peak 2–3 days after symptom onset, whereas influenza symptom onset is constant and immediate. The symptoms usually resolve spontaneously in 7 to 10 days but some can last for up to three weeks.

The first indication of an upper respiratory virus is often a sore or scratchy throat. Other common symptoms are runny nose, congestion, and sneezing. These are sometimes accompanied by muscle aches, fatigue, malaise, headache, weakness, or loss of appetite. Cough and fever generally indicate influenza rather than an upper respiratory virus with a positive predictive value of around 80%.Symptoms may be more severe in infants and young children, and in these cases it may include fever and hives. Upper respiratory viruses may also be more severe in smokers.

Prevention

The best way to avoid a cold is thorough and regular washing of the hands. This resulted in a 16% decrease in the rate of respiratory infections and as much as a 20% decrease in the common cold. Anti-bacterial and non anti-bacterial soaps are equally effective. Alcohol-based hand sanitizers also reduce viruses significantly and are recommended as a method in health care environments. The use of alcohol based hand gels in the home reduced rate of transmission of respiratory illnesses among family members.

Probiotics in children 3 – 5 years old were found effective in decreases cold symptoms when taken over 6 months.

Developing a vaccine for the common cold as of 2009 has been unsuccessful. This is due to a number of reason including: a large variety of viruses and the fact that they mutate rapidly. Many thus believe that successful immunization is highly improbable.

Management

Poster encouraging citizens to "Consult your Physician" for treatment of the common cold
There are no medications or herbal remedies proven to shorten the duration of illness. Treatment is symptomatic support usually via analgesics for fever, headache and myalgia, nasal decongestants, and lozenges for sore throat.

The common cold usually resolves spontaneously in 7 to 10 days, but some symptoms can last for up to three weeks. A history of smoking extends the duration of illness about three days.

Conservative

Treatments that help alleviate symptoms include simple analgesics such as ibuprofen, and acetaminophen.

Evidence does not show that cold medicines are any more effective than simple analgesics. They are not recommended for use in children due to no evidence supporting their effectiveness and the potential of harm.

Getting plenty of rest, drinking fluids to maintain hydration, gargling with warm salt water, or use of over-the-counter pain medicines are reasonable conservative measures. Saline nasal drops may help alleviate nasal congestion.

Evidence for encouraging the active intake of fluids in acute respiratory infections is lacking as is the use of heated humidified air.

Antibiotics and antivirals

Antibiotics are not effective against the viruses that causes the common cold and due to their side effects cause overall harm. There are no approved antiviral drugs for the common cold even though some priliminary research has shown benefit.

Alternative treatments

Many alternative treatments are used to treat the common cold. None however are recommended due to insufficient scientific evidence. Some alternative treatments, like echinacea, have not been shown to have any effects on the frequency of infection, the duration of infection, or the severity of symptoms of the common cold. Other alternative treatments which similarly lack solid scientific evidence include calendula, ginger, garlic and vitamin C supplements.

While vitamin C in normal or increased doses has not been shown to be beneficial in a normal population for the prevention or treatment of the common cold, it might be beneficial in people exposed to periods of severe physical exercise or cold environments.

Prognosis

The common cold is generally mild and self-limiting.

Epidemiology

Upper respiratory tract infections are the most common infectious diseases among adults, who have two to four respiratory infections annually. Children may have six to ten colds a year (and up to 12 colds a year for school children). In the United States, the incidence of colds is higher in the fall (autumn) and winter, with most infections occurring between September and April. The seasonality may be due to the start of the school year, or due to people spending more time indoors (thus in closer proximity with each other) increasing the chance of transmission of the virus.

History



The name "common cold" came into use in the 16th century, due to the similarity between its symptoms and those of exposure to cold weather. Norman Moore relates in his history of the Study of Medicine that James I continually suffered from nasal colds, which were then thought to be caused by polypi, sinus trouble, or autotoxaemia.

In the 18th century, Benjamin Franklin considered the causes and prevention of the common cold. After several years of research he concluded: "People often catch cold from one another when shut up together in small close rooms, coaches, etc. and when sitting near and conversing so as to breathe in each other's transpiration." Although viruses had not yet been discovered, Franklin hypothesized that the common cold was passed between people through the air. He recommended exercise, bathing, and moderation in food and drink consumption to avoid the common cold. Franklin's theory on the transmission of the cold was confirmed some 150 years later.

Common Cold Unit

In the United Kingdommarker, the Common Cold Unit was set up by the 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, two years after it completed research of zinc gluconate lozenges in the prophylaxis and treatment of rhinovirus colds, the only successful treatment in the history of the unit.

Social and cultural

Economic cost



In the United States, the common cold leads to 75 to 100 million physician visits annually at a conservative cost estimate of $7.7 billion per year. Americans spend $2.9 billion on over-the-counter drugs and another $400 million on prescription medicines for symptomatic relief.

More than one-third of patients who saw a doctor received an antibiotic prescription, which has implications for antibiotic resistance from overuse of such drugs.

An estimated 22 to 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 150 million workdays missed by employees suffering from a cold, the total economic impact of cold-related work loss exceeds $20 billion per year. This accounts for 40% of time lost from work.

Legal

Canada in 2009 restricted the use of over-the-counter cough and cold medication in children 6 years and under due to concerns regarding risks and unproven benefits.

Research

Biota Holdings are developing a drug, currently know as BTA798, which targets rhinovirus. The drug has recently successfully completed Phase IIa clinical trials.

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.Schering-Plough is developing an intra-nasal formulation that may have fewer adverse effects.

Researchers from University of Maryland, College Parkmarker and University of Wisconsin–Madisonmarker have mapped the genome for all known virus strains that cause the common cold.

See also



References

External links




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