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Common cold
SpecialtyFamily medicine, infectious diseases, otorhinolaryngology Edit this on Wikidata

The common cold (also known as nasopharyngitis, rhinopharyngitis, acute coryza, or a cold) is a viral infectious disease of the upper respiratory system which affects primarily the nose. Symptoms include a cough, sore throat, runny nose, and fever which usually resolve in seven to ten days, with some symptoms possibly lasting up to three weeks. Well more than 200 viruses are implicated in the cause of the common cold; the rhinoviruses are the most common.

Upper respiratory tract infections are loosely divided by the areas they affect, with the common cold primarily affecting the nose, the throat (pharyngitis), and the sinuses (sinusitis). Symptoms are mostly due to the body's immune response to the infection rather than to tissue destruction by the viruses themselves. The primary method of prevention is by hand washing with some evidence to support the effectiveness of wearing face masks.

There is no cure for the common cold but the symptoms can be treated. It is the most frequent infectious disease in humans with the average adult contracting two to three colds a year and the average child contracting between six and twelve. These infections have been with humankind since antiquity.

Signs and symptoms

The typical symptoms of a cold include cough, runny nose, nasal congestion and a sore throat, sometimes accompanied by muscle ache, fatigue, headache, and loss of appetite.[1] A sore throat is present in about 40% of the cases and a cough in about 50%,[2] while muscle ache occurs in about half.[3] In adults, a fever is generally not present but it is common in infant and young children.[3] The cough is usually mild in contrast to that accompanying influenza.[3] While a cough and a fever indicate a higher likelihood of influenza in adults, there is a great deal of similarity between these two conditions.[4] A number of the viruses that cause the common cold may also result in asymptomatic infections.[5][6]

Progression

A cold usually begins with fatigue, a feeling of being chilled, sneezing and a headache, followed in a couple of days by a runny nose and cough.[1] Symptoms typically peak two to three days after infection onset,[3] and usually resolve in seven to ten days but some can last for up to three weeks.[7] In children, the cough lasts for more than ten days in 35–40% of the cases and continues for more than 25 days in 10%.[8]

Cause

Viruses

Coronaviruses are a group of viruses known for causing the common cold. They have a halo, or crown-like (corona) appearance when viewed under an electron microscope.

The common cold is a viral infection of the upper respiratory tract. The most commonly implicated virus is a rhinovirus (30–80%), a type of picornavirus with 99 known serotypes.[9][10] Others include: coronavirus (10–15%), influenza (5–15%),[3] human parainfluenza viruses, human respiratory syncytial virus, adenoviruses, enteroviruses, and metapneumovirus.[11] Frequently more than one virus is present.[12] In total over 200 different viral types are associated with colds.[3]

Transmission

The common cold virus is typically transmitted either via airborne droplets or contact with infected nasal secretions or other contaminated objects.[2][13] Which of these routes is of primary importance has not been determined.[14] The viruses may survive for prolonged periods in the environment and they can be picked up by people's hands and subsequently carried to their eyes or nose where infection occurs.[13] People sitting in close proximity also appear at greater risk.[14] There is no evidence that recirculated air during commercial flight is a method of transmission.[13] Rhinovirus-caused colds are most infectious during the first three days of symptoms.[15]

Weather

The traditional folk theory is that a cold can be "caught" by prolonged exposure to cold weather such as rain or winter conditions, which is how the disease got its name.[16] The role of body cooling as a risk factor the common cold is controversial.[17] Some of the viruses that cause the common colds are seasonal, occurring more frequently during cold or wet weather.[18] This is believed to be due primarily to increased time spent indoors, which puts people in close proximity; however, it may also be related to changes in the respiratory system that results in greater susceptibility.[19] Low humidity increases viral transmission rates potentially due to dry air allowing small viral droplets to disperse farther and stay in the air longer.[20]

Other

Herd immunity, generated from previous exposure to cold viruses, plays an important role in limiting viral spread, as seen with younger populations have greater rates of respiratory infections.[21] Poor immune function is also a risk factor for disease.[21][22] Getting too little sleep and malnutrition has been associated with a greater risk of developing an infection when exposed to a rhinovirus and this is believed to be due to their importance in proper immune function.[23][24]

Pathophysiology

The common cold is a disease of the upper respiratory tract.

The symptoms of the common cold are believed to be primarily related to the immune response to the virus.[25] The mechanism of this immune response is virus specific. For example, the rhinovirus is typically acquired by direct contact; it binds to human ICAM-1 receptors through unknown mechanisms to trigger the release of inflammatory mediators.[25] These inflammatory mediators then produce the symptoms.[25] It does not generally cause damage to the nasal epithelium.[3] The respiratory syncytial virus (RSV) on the other hand is contacted by both direct contact and air born droplets. It then replicates in the nose and throat before frequently spreading to the lower respiratory tract.[26] RSV does cause epithelium damage.[26] Human parainfluenza virus typically results in inflammation of the nose, throat, and bronchi.[27] In young children when it affects the trachea it may produce the symptoms of croup due to the small size of their airway.[27]

Diagnosis

The distinction between different viral upper respiratory tract infections is loosely based on the location of symptoms with the common cold affecting primarily the nose, pharyngitis affecting the throat, and bronchitis affecting the lungs.[2] There however can be significant overlap and multiple areas can be affected.[2] The common cold is frequently defined as nasal inflammation with varying amount of throat inflammation.[28] Self diagnosis is frequent.[3] Isolation of the actual viral agent involved is rarely performed,[28] and it is generally not possible to identify the virus type through symptoms.[3]

Prevention

Physical measure to prevent the spread of cold viruses has been deemed the only potentially effective measure for prevention.[29] These measures include primarily hand-washing and face masks but also in the health care environment gowns and disposable gloves.[29] Efforts such as quarantine are not possible as the disease is so wide spread and symptoms are none specific, vaccination has proved difficult as there are so many viruses involved and they change rapidly.[29] Successful creation of a broadly effective vaccine is thus highly improbable.[30]

Regular hand washing appears to be effective at reducing the transmission of cold viruses especially among children.[31] Whether the addition of antivirals or antibacterials to normal hand-washing provides greater benefit is unknown.[31] Wearing face masks when around people who are infected may be beneficial however there is insufficient evidence for maintaining a greater social distance.[31] Zinc supplementation may be effective at decreasing the rate of colds.[32] Routine vitamin C supplementation does not reduce the risk or severity of the common cold, though it may reduce the duration of illness.[33]

Management

Poster encouraging citizens to "Consult your Physician" for treatment of the common cold

There are currently no medications or herbal remedies which have been conclusively demonstrated to shorten the duration of infection.[34] Treatment thus comprises symptomatic relief.[35] Getting plenty of rest, drinking fluids to maintain hydration, and gargling with warm salt water, are reasonable conservative measures.[11] Much of the benefit from treatment is however attributed to the placebo effect.[36]

Symptomatic

Treatments that help alleviate symptoms include simple analgesics and antipyretics such as ibuprofen[37] and acetaminophen / paracetamol.[38] Evidence does not show that cough medicines are any more effective than simple analgesics[39] and they are not recommended for use in children due to a lack of evidence supporting effectiveness and the potential for harm.[40][41] 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.[40] The misuse of dextromethorphan (an over the counter cough medicine) has lead to its ban in a number of countries.[42]

In adults the symptoms of a runny nose can be reduced by first generation antihistamines; however, they are associated with adverse effects such as drowsiness.[35] Other decongestants such as pseudoephedrine are also effective in this population.[43] Ipratropium nasal spray may reduce the symptoms of a runny nose but there is little effect on stuffiness.[44] Second-generation antihistamines however do not appear to be effective.[45]

Due to lack of studies, it is not currently known whether increased fluid intake improves symptoms or shortens respiratory illness[46] and a similar lack of data exists for the use of heated humidified air.[47] One study has found chest vapor rub to be effective at providing some symptomatic relief of nocturnal cough, congestion, and sleep difficulty.[48]

Antibiotics and antivirals

Antibiotics have no effect against viral infections and thus have no effect against the viruses that cause the common cold.[49] Due to their side effects they cause overall harm however are still frequently prescribed.[49][50] There are no effective antiviral drugs for the common cold even though some preliminary research has shown benefit.[35][51]

Alternative treatments

While many alternative treatments are used for the common cold there is insufficient scientific evidence to support the use of most.[35] As of 2010 there is insufficient evidence to recommend for or against either honey or nasal irrigation.[52][53] Zinc supplements may somewhat reduce the severity and duration of symptoms when taken within 24 hours of their onset.[32] Vitamin C's effect on the common cold while extensively researched is disappointing, except in limited circumstances, specifically, individuals exercising vigorously in cold environments.[33][54] Evidence about the usefulness of echinacea inconsistent.[55][56] Different types of echinacea supplements may vary in their effectiveness.[55]

Prognosis

The common cold is generally mild and self-limiting with most symptoms generally improving in a week.[2] Severe complications, if they occur, are usually in the very old, the very young or those who are immunosuppressed.[57] Secondary bacterial infections may occur resulting in sinusitis, pharyngitis, or an ear infection.[58] It is estimated that sinusitis occurs in 8% and an ear infection in 30% of cases.[59]

Epidemiology

The common cold is the most common human disease.[57] Adults have two to five infections annually[2][3] and children may have six to ten colds a year (and up to 12 colds a year for school children).[35] Rates of symptomatic infections increase in the elderly due to due to a worsening immune system.[21]

History

While the cause of the common cold has only been identified since the 1950s the disease has been with humankind since antiquity.[60] Its symptoms and treatment is described in the Egyptian Ebers papyrus, the oldest existing medical text, written before the 16th century BCE.[61] 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.[62]

In the United Kingdom, the Common Cold Unit was set up by the Medical Research Council in 1946 and it was here that the rhinovirus was discovered 1956.[63] In the 1970s, the CCU demonstrated that treatment with interferon during the incubation phase of rhinovirus infection protects somewhat against the disease,[64] 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.[65]

Economic impact

A British poster from World War II describing the cost of the common cold[66]

The economic impact of the common cold is poorly understood in much of the world.[67] 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.[68] More than one-third of people who saw a doctor received an antibiotic prescription, which has implications for antibiotic resistance.[68] 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.[11][68] This accounts for 40% of time lost from work in the United States.[69]

Research

A number of antivirals have been tested for effectiveness in the common cold; however as of 2009 none have been both found effective and licensed for use.[70] There are ongoing trials of the anti-viral drug pleconaril which shows promise against picornaviruses as well as trials of BTA-798.[71] The oral form of pleconaril had safety issues and an aerosol form is being studied.[71]

Researchers from University of Maryland, College Park and University of Wisconsin–Madison have mapped the genome for all known virus strains that cause the common cold.[72]

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References
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