The common cold (acute viral rhinopharyngitis, acute coryza, viral upper respiratory tract infection, 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.
Common 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. Around 30-50% of colds are caused by rhinoviruses.
A 2009 study found that low blood serum levels of vitamin D were associated with increased rates of the common cold. A randomized controlled trial found that 104 post-menopausal African American women living in New York given vitamin D were three times less likely to report cold and flu symptoms than 104 placebo controls. A low dose (800 IU/day) not only reduced reported incidence, it abolished the seasonality of reported colds and flu. A higher dose (2000 IU/day), given during the last year of the trial, virtually eradicated all reports of colds or flu.
Exposure to 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 University 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.
Common Cold 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. 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. 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. 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%. Upper respiratory viruses may also be more severe in smokers.
Common Cold Prevention
The best way to avoid a cold is to wash hands thoroughly and regularly; and to avoid touching the eyes, nose, mouth, and face. Anti-bacterial soaps have no extraordinary effect on the cold virus; it is the mechanical action of hand washing with the soap that removes the virus particles. Rhinoviruses can live up to 3 hours outside the body on the skin or objects.
Alcohol-based hand sanitizer however does not completely eliminate the cold-causing rhinovirus.
Neither soap and water nor alcohol gels provide 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.
Probiotics in children 3 – 5 years old were found effective in decreases cold symptoms when taken over 6 months.
Common Cold Management
The common cold usually resolves spontaneously in 7 to 10 days, but some symptoms can last for up to three weeks. 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.
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 there 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.
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 only target bacteria and thus do not have any beneficial effect in the common cold. There are no approved antiviral drugs for the common cold.
Many alternative treatments are used to treat the common cold. None, however, are supported by solid 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.
Common Cold Prognosis
Although the disease is generally mild and self-limiting, patients with common colds often seek professional medical help, use over-the-counter drugs, and may miss school or work days. The annual cumulative societal cost of the common cold in developed countries is considerable in terms of money spent on remedies, and hours of lost productivity.
There are no antiviral drugs approved to treat or cure the infection; all medications used are palliative and treat symptoms only. Alternative treatments such as vitamin C, echinacea, and zinc have been proposed but none of them has been shown to decrease the duration of the illness, hands has been found effective, as this minimizes person-to-person transmission of the virus.
Common Cold 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. 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 Kingdom, 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.
Common Cold Social and cultural
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.
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 and University of Wisconsin–Madison have mapped the genome for all known virus strains that cause the common cold.
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