There is novaccine for the common cold.[3] This is due to the rapid mutation and wide variation of viruses that cause the common cold.[17] The primary methods of prevention arehand washing; not touching the eyes, nose or mouth with unwashed hands; andstaying away from sick people.[3] People are considered contagious as long as the symptoms are still present.[18] Some evidence supports the use offace masks.[10] There is also nocure, but the symptoms can be treated.[3]Zinc may reduce the duration and severity of symptoms if started shortly after the onset of symptoms.[11]Nonsteroidal anti-inflammatory drugs (NSAIDs) such asibuprofen may help with pain.[12]Antibiotics, however, should not be used, as all colds are caused by viruses rather than bacteria.[19] There is no good evidence thatcough medicines are effective.[6][20]
The common cold is the most frequent infectious disease in humans.[21] Under normal circumstances, the average adult gets two to three colds a year, while the average child may get six to eight colds a year.[8][13] Infections occur more commonlyduring the winter.[3] These infections have existed throughout human history.[22]
Signs and symptoms
Woman with symptoms of the common cold
The typical symptoms of a cold includecough,runny nose,sneezing,nasal congestion, and asore throat, sometimes accompanied bymuscle ache,fatigue,headache, andloss of appetite.[23] A sore throat is present in about 40% of cases, a cough in about 50%,[8] and muscle aches in about 50%.[4] In adults, afever is generally not present but it is common in infants and young children.[4] The cough is usually mild compared to that accompanyinginfluenza.[4] While a cough and a fever indicate a higher likelihood of influenza in adults, a great deal of similarity exists between these two conditions.[24] A number of the viruses that cause the common cold may also result inasymptomatic infections.[25][26]
The color of themucus or nasal secretion may vary from clear to yellow to green and does not indicate the class of agent causing the infection.[27]
Progression
Cold symptoms over time
A cold usually begins with fatigue, a feeling of beingchilled, sneezing, and a headache, followed in a couple of days by a runny nose and cough.[23] Symptoms may begin within sixteen hours of exposure[28] and typically peak two to four days after onset.[4][29] They usually resolve in seven to ten days, but some can last for up to three weeks.[7] The average duration of cough is eighteen days[30] and in some cases people develop apost-viral cough which can linger after the infection is gone.[31] In children, the cough lasts for more than ten days in 35–40% of cases and continues for more than 25 days in 10%.[32]
Causes
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 an infection of the upperrespiratory tract which can be caused by many different viruses. The most commonly implicated is arhinovirus (30–80%), a type ofpicornavirus with 99 knownserotypes.[33] Other commonly implicated viruses includecoronaviruses,adenoviruses,enteroviruses,parainfluenza andRSV.[34] Frequently more than one virus is present.[35] In total, more than 200 viral types are associated with colds.[4] The viral cause of some common colds (20–30%) is unknown.[34]
Transmission
The common cold virus is typically transmitted via airborne droplets, direct contact with infected nasal secretions, orfomites (contaminated objects).[8][36] Which of these routes is of primary importance has not been determined.[37] As with all respiratory pathogens once presumed to transmit via respiratory droplets, it is highly likely to be carried by the aerosols generated during routine breathing, talking, and singing.[38] The viruses may survive for prolonged periods in the environment (over 18 hours for rhinoviruses) and can be picked up by people's hands and subsequently carried to their eyes or noses where infection occurs.[36] Transmission from animals is considered highly unlikely; an outbreak documented at a British scientific base onAdelaide Island after seventeen weeks of isolation was thought to have been caused by transmission from a contaminated object or an asymptomatic human carrier, rather than from thehusky dogs which were also present at the base.[39]
Transmission is common in daycare and schools due to the proximity of many children with little immunity and poor hygiene.[40] These infections are then brought home to other members of the family.[40] There is no evidence that recirculated air during commercial flight is a method of transmission.[36] People sitting close to each other appear to be at greater risk of infection.[37]
Other
Herd immunity, generated from previous exposure to cold viruses, plays an important role in limiting viral spread, as seen with younger populations that have greater rates of respiratory infections.[41] Poor immune function is a risk factor for disease.[41][42]Insufficient sleep andmalnutrition have been associated with a greater risk of developing infection following rhinovirus exposure; this is believed to be due to their effects on immune function.[43][44]Breast feeding decreases the risk ofacute otitis media andlower respiratory tract infections among other diseases,[45] and it is recommended that breast feeding be continued when an infant has a cold.[46] In the developed world breast feeding may not be protective against the common cold in and of itself.[47]
The symptoms of the common cold are believed to be primarily related to theimmune response to the virus.[15] The mechanism of this immune response is virus-specific. For example, the rhinovirus is typically acquired by direct contact; it binds to humans viaICAM-1 receptors and theCDHR3 receptor through unknown mechanisms to trigger the release ofinflammatory mediators.[15] These inflammatory mediators then produce the symptoms.[15] It does not generally cause damage to the nasalepithelium.[4] The respiratory syncytial virus (RSV), on the other hand, is contracted by direct contact and airborne droplets. It then replicates in the nose and throat before spreading to thelower respiratory tract.[48] RSV does cause epithelium damage.[48] Humanparainfluenza virus typically results in inflammation of the nose, throat, andbronchi.[49] In young children, when it affects thetrachea, it may produce the symptoms ofcroup, due to the small size of their airways.[49]
Diagnosis
The distinction between viralupper respiratory tract infections is loosely based on the location of symptoms, with the common cold affecting primarily the nose (rhinitis), throat (pharyngitis), and lungs (bronchitis).[8] There can be significant overlap, and more than one area can be affected.[8] Self-diagnosis is frequent.[4] Isolation of the viral agent involved is rarely performed,[50] and it is generally not possible to identify the virus type through symptoms.[4]
Prevention
The only useful ways to reduce the spread of cold viruses are physical andengineering measures[10] such as usingcorrect hand washing technique,respirators, and improvement of indoor air. In the healthcare environment, gowns and disposable gloves are also used.[10] Droplet precautions cannot reliably protect againstinhalation of common-cold-laden aerosols. Instead, airborne precautions such asrespirators,ventilation, andHEPA/high MERV filters, are the only reliable protection against cold-laden aerosols.[38] Isolation orquarantine is not used as the disease is so widespread and symptoms are non-specific. There is no vaccine to protect against the common cold.[51]Vaccination has proven difficult as there are so many viruses involved and because theymutate rapidly.[10][52] Creation of a broadly effective vaccine is, therefore, highly improbable.[53]
Regular hand washing appears to be effective in reducing the transmission of cold viruses, especially among children.[54] Whether the addition ofantivirals orantibacterials to normal hand washing provides greater benefit is unknown.[54] Wearing face masks when around people who are infected may be beneficial; however, there is insufficient evidence for maintaining a greatersocial distance.[54]
It is unclear whetherzinc supplements affect the likelihood of contracting a cold.[55]
Management
Poster from 1937 encouraging citizens to "consult your physician" for treatment of the common cold
Treatments of the common cold primarily involvemedications and other therapies for symptomatic relief.[13] Getting plenty of rest, drinking fluids to maintain hydration, andgargling with warm salt water are reasonable conservative measures.[56] Much of the benefit from symptomatic treatment is, however, attributed to theplacebo effect.[57] As of 2010,[update] no medications or herbal remedies had been conclusively demonstrated to shorten the duration of infection.[58]
Symptomatic
Various treatments for the common cold - liquid and pill cold medicine, tea, throat lozenges, and over-the-counter decongestants.
Treatments that may help with symptoms includepain medication andmedications for fevers such asibuprofen[12] andacetaminophen (paracetamol).[59] However, it is not clear whether acetaminophen helps with symptoms.[60] It is not known if over-the-countercough medications are effective for treating anacute cough.[61] Cough medicines are not recommended for use in children due to a lack of evidence supporting effectiveness and the potential for harm.[62][63] In 2009, Canada restricted the use ofover-the-counter cough and cold medication in children six years and under due to concerns regarding risks and unproven benefits.[62] The misuse ofdextromethorphan (an over-the-counter cough medicine) has led to its ban in a number of countries.[64]Intranasal corticosteroids have not been found to be useful.[65]
In adults, short term use ofnasal decongestants may have a small benefit.[66]Antihistamines may improve symptoms in the first day or two; however, there is no longer-term benefit and they have adverse effects such as drowsiness.[67] Other decongestants such aspseudoephedrine appear effective in adults.[68][66] Combined oral analgesics, antihistaminics, and decongestants are generally effective for older children and adults.[69]Ipratropium nasal spray may reduce the symptoms of a runny nose but has little effect on stuffiness.[70] Ipratropium may also help with coughs in adults.[71] The safety and effectiveness of nasal decongestant use in children is unclear.[66]
Due to lack of studies, it is not known whether increased fluid intake improves symptoms or shortens respiratory illness.[72] As of 2017, heated and humidified air, such as via RhinoTherm, is of unclear benefit.[73] One study has foundchest vapor rub to provide some relief of nocturnal cough, congestion, and sleep difficulty.[74]
Some experts advise againstphysical exercise if there are symptoms such as fever, widespreadmuscle aches orfatigue.[75][76] It is regarded as safe to perform moderate exercise if the symptoms are confined to thehead, includingrunny nose,nasal congestion,sneezing, or a minorsore throat.[75][76] There is a popular belief that having a hot drink can help with cold symptoms, but evidence to support this is very limited.[77]
Antibiotics and antivirals
Antibiotics have no effect against viral infections, including the common cold.[78] Due to their side effects, antibiotics cause overall harm but nevertheless are still frequently prescribed.[78][79] Some of the reasons that antibiotics are so commonly prescribed include people's expectations for them, physicians' desire to help, and the difficulty in excluding complications that may be amenable to antibiotics.[80] There are no effectiveantiviral drugs for the common cold even though some preliminary research has shown benefits.[13][81]
Zinc supplements may shorten the duration of colds by up to 33% and reduce the severity of symptoms if supplementation begins within 24 hours of the onset of symptoms.[11][55][82][83][84] Some zinc remedies directly applied to the inside of the nose have led to theloss of the sense of smell.[11][85] A 2017 review did not recommend the use of zinc for the common cold for various reasons;[20] whereas a 2017 and 2018 review both recommended the use of zinc, but also advocated further research on the topic.[82][83]
Vitamin Csupplementation does not affect the incidence of the common cold, but may reduce its duration if taken on a regular basis.[90] There is no conclusive evidence thatvitamin D supplementation is efficacious in the prevention or treatment of respiratory tract infections.[91]
Prognosis
The common cold is generally mild and self-limiting with most symptoms generally improving in a week.[8] In children, half of cases resolve in 10 days and 90% in 15 days.[92] Severe complications, if they occur, are usually in the very old, the very young, or those who areimmunosuppressed.[21] Secondary bacterial infections may occur resulting insinusitis,pharyngitis, or anear infection.[93] It is estimated that sinusitis occurs in 8% and ear infection in 30% of cases.[94]
Epidemiology
The common cold is the most common human disease[21] and affects people all over the globe.[40] Adults typically have two to three infections annually,[8] and children may have six to ten colds a year (and up to twelve colds a year for school children).[13] Rates of symptomatic infections increase in the elderly due to declining immunity.[41]
Weather
A common misconception is that one can "catch a cold" merely through prolonged exposure to cold weather.[95] Although it is now known that colds are viral infections, the prevalence of many such viruses are indeed seasonal, occurring more frequently during cold weather.[96] The reason for the seasonality has not been conclusively determined.[97] Possible explanations may include cold temperature-induced changes in the respiratory system,[98] decreased immune response,[99] and low humidity causing an increase in viral transmission rates, perhaps due to dry air allowing small viral droplets to disperse farther and stay in the air longer.[100]
The apparent seasonality may also be due to social factors, such as people spending more time indoors near infected people,[98] and especially children at school.[40][97] Although normal exposure to cold does not increase one's risk of infection, severe exposure leading to significant reduction of body temperature (hypothermia) may put one at a greater risk for the common cold: although controversial, the majority of evidence suggests that it may increase susceptibility to infection.[99]
History
A British poster fromWorld War II describing the cost of the common cold[101]
While the cause of the common cold was identified in the 1950s, the disease appears to have been with humanity since its early history.[22] Its symptoms and treatment are described in the EgyptianEbers papyrus, the oldest existing medical text, written before the 16th century BCE.[102] The name "cold" came into use in the 16th century, due to the similarity between its symptoms and those of exposure to cold weather.[103]
In the United Kingdom, theCommon Cold Unit (CCU) was set up by theMedical Research Council in 1946 and it was where the rhinovirus was discovered in 1956.[104] In the 1970s, the CCU demonstrated that treatment withinterferon during the incubation phase of rhinovirus infection protects somewhat against the disease,[105] but no practical treatment could be developed. The unit was closed in 1989, two years after it completed research ofzinc gluconate lozenges in the prevention and treatment of rhinovirus colds, the only successful treatment in the history of the unit.[106]
Research directions
Antivirals have been tested for effectiveness in the common cold; as of 2009, none had been both found effective and licensed for use.[81] There are trials of the anti-viral drugpleconaril which shows promise againstpicornaviruses as well as trials of BTA-798.[107] The oral form of pleconaril had safety issues and an aerosol form is being studied.[107] Thegenomes of all known human rhinovirus strains have been sequenced.[108]
Societal impact
The economic impact of the common cold is not well understood in much of the world.[94] In the United States, the common cold leads to 75–100 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 symptom relief.[109] More than one-third of people who saw a doctor received an antibiotic prescription, which has implications forantibiotic resistance.[109] An estimated 22–189 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 who have a cold, the total economic impact of cold-related work loss exceeds $20 billion per year.[56][109] This accounts for 40% of time lost from work in the United States.[110]
^abcdefghiArroll B (March 2011)."Common cold".BMJ Clinical Evidence.2011 (3): 1510.PMC3275147.PMID21406124.Common colds are defined as upper respiratory tract infections that affect the predominantly nasal part of the respiratory mucosa
^abcd"Zinc – Fact Sheet for Health Professionals". Office of Dietary Supplements, US National Institutes of Health. 10 July 2019.Archived from the original on 25 March 2021. Retrieved27 December 2019.Although studies examining the effect of zinc treatment on cold symptoms have had somewhat conflicting results, overall zinc appears to be beneficial under certain circumstances.... In September of 2007, Caruso and colleagues published a structured review of the effects of zinc lozenges, nasal sprays, and nasal gels on the common cold [69]. Of the 14 randomized, placebo-controlled studies included, 7 (5 using zinc lozenges, 2 using a nasal gel) showed that the zinc treatment had a beneficial effect and 7 (5 using zinc lozenges, 1 using a nasal spray, and 1 using lozenges and a nasal spray) showed no effect. More recently, a Cochrane review concluded that "zinc (lozenges or syrup) is beneficial in reducing the duration and severity of the common cold in healthy people, when taken within 24 hours of onset of symptoms" [73]. The author of another review completed in 2004 also concluded that zinc can reduce the duration and severity of cold symptoms [68]. However, more research is needed to determine the optimal dosage, zinc formulation and duration of treatment before a general recommendation for zinc in the treatment of the common cold can be made [73]. As previously noted, the safety of intranasal zinc has been called into question because of numerous reports of anosmia (loss of smell), in some cases long-lasting or permanent, from the use of zinc-containing nasal gels or sprays [17–19].
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^Turner RB, Hayden FG (2003)."Rhinovirus". In Rübsamen-Waigmann H, et al. (eds.).Viral Infections and Treatment. New York: CRC Press. p. 111.ISBN978-0-8247-4247-8.Archived from the original on 4 May 2016.
^abcdPapadopoulos NG, Xatzipsaltis M, Johnston SL (2009)."Rhinoviruses". In Zuckerman AJ, et al. (eds.).Principles and Practice of Clinical Virology (6th ed.). John Wiley & Sons. p. 496.ISBN978-0-470-74139-9.Archived from the original on 3 June 2016.
^McNiel ME, Labbok MH, Abrahams SW (July 2010). "What are the risks associated with formula feeding? A re-analysis and review".Breastfeeding Review.18 (2):25–32.PMID20879657.
^CDC (11 February 2019)."Common Colds".Centers for Disease Control and Prevention.Archived from the original on 27 September 2020. Retrieved18 September 2020.
^Vassilev ZP, Kabadi S, Villa R (March 2010). "Safety and efficacy of over-the-counter cough and cold medicines for use in children".Expert Opinion on Drug Safety.9 (2):233–42.doi:10.1517/14740330903496410.PMID20001764.S2CID12952868.
^Wu T, Zhang J, Qiu Y, Xie L, Liu GJ (January 2007). "Chinese medicinal herbs for the common cold".The Cochrane Database of Systematic Reviews (1): CD004782.doi:10.1002/14651858.CD004782.pub2.PMID17253524.
^abMourtzoukou EG, Falagas ME (September 2007). "Exposure to cold and respiratory tract infections".The International Journal of Tuberculosis and Lung Disease.11 (9):938–43.PMID17705968.
^abcFendrick AM, Monto AS, Nightengale B, Sarnes M (February 2003). "The economic burden of non-influenza-related viral respiratory tract infection in the United States".Archives of Internal Medicine.163 (4):487–94.doi:10.1001/archinte.163.4.487.PMID12588210.S2CID10169748.
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