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The Common cold (also known as nasopharyngitis, acute viral rhinopharyngitis, acute coryza, or a cold) (Latin: rhinitis acuta catarrhalis) is a viral infectious disease of the upper respiratory system, caused primarily by rhinoviruses and coronaviruses. Common symptoms include a cough, sore throat, runny nose, and fever. There is currently no known treatment that shortens the duration; however, symptoms usually resolve spontaneously in 7 to 10 days, with some symptoms possibly lasting for up to three weeks.
The common cold is the most frequent infectious disease in humans with the average adult contracting two to four infections a year and the average child contracting between 6 12.
Etiology Viruses
The common cold is a viral infection of the upper respiratory tract. The most commonly implicated virus is a rhinovirus (30 50%), a type of picornavirus with 99 known serotypes. Others include: coronavirus (10 15%), influenza (5 15%),] human parainfluenza viruses, human respiratory syncytial virus, adenoviruses, enteroviruses, and metapneumovirus.
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.
Risk factors
- Touching eyes, nose, or mouth with contaminated fingers. This behavior increases the likelihood of transferring viruses from the surface of the hands, where they are harmless, into the upper respiratory tract, where they can infect the tissues. It has been demonstrated that cold viruses can be spread by touching contaminated objects and surfaces, or by brief contact of hands.
- Spending time in an enclosed area with an infected person or in close contact with an infected person. Common colds are droplet-borne infections, which means that they can be transmitted through breathing in tiny particles that the infected person emits when he or she coughs or sneezes. In one study, the virus was recovered in 1/13 of sneezes and 0/8 coughs generated by adults with natural rhinovirus (cold) infections.
- The role of body cooling in causing the common cold is controversial.]It is the most commonly offered folk explanation for the disease, and it has received some experimental evidence. One study showed that exposure to the cold causes cold symptoms in about 10% of those exposed, and that the subjects experiencing this effect report far more colds overall than those who do not. However, a variety of other studies do not show such an effect
- A history of smoking extends the duration of illness by about three days.
- Getting fewer than seven hours of sleep per night has been associated with a risk three times higher of developing an infection when exposed to a rhinovirus, compared to those who sleep more than eight hours per night.
- Common colds are seasonal, occurring more frequently during winter outside of tropical zones. Some argue that this is partly due to a change in behaviors such as increased time spent indoors, which puts infected people in close proximity to other people, rather than to exposure to cold temperatures.
- Low humidity increases viral transmission rates. One theory is that dry air causes evaporation of water, thus allowing small viral droplets to disperse farther and stay in the air longer.
- Counterintuitively, people with stronger immune systems are more likely to develop symptomatic colds. This is because the symptoms of a cold are directly due to the strong immune response to the virus, not the virus itself. People with less active immune systems about a quarter of adults get infected with the viruses, but the relatively weak immunological response produces no significant or identifiable symptoms. These people are asymptomatic carriers and can unknowingly spread the virus to other people. Because strong immune responses cause cold symptoms, “boosting” the immune system increases cold symptoms.
Pathophysiology
- The common cold is a disease of the upper respiratory tract.
- The common cold is a type of pharyngitis (inflammation of the throat). In the common cold, the inflammation is caused by a viral infection in the uppermost part of the throat (the nasopharynx), which runs from behind the nose down to the mouth.
- The common cold virus is transmitted mainly from contact with saliva or nasal secretions of an infected person, either directly, when a healthy person breathes in the virus-laden aerosol generated when an infected person coughs or sneezes, or by touching a contaminated surface and then touching the nose or eyes.
- 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, and increases ICAM-1 production, which in turn helps the immune response against the virus.] 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.
Prevention
The best prevention for the common cold is staying away from people who are infected, and places where infected individuals have been.
Regular hand washing is recommended to reduce transmission of cold viruses and other pathogens via direct contact. Virus can be recovered from the hands of ?40% of adults with rhinovirus colds, and the quantity of virus recovered from the hands is also generally greater than that recovered in coughs and sneezes. Washing of the hands reduces virus count on the skin.
- Hand washing with plain soap and water is recommended. The mechanical action of hand rubbing with plain soap, rinsing, and drying physically removes the virus particles off the hands.
- Alcohol-based hand sanitizers provide very little protection against upper respiratory infections, especially among children.
- Because the common cold is caused by a virus instead of a bacterium, anti-bacterial soaps are no better than regular soap for removing the virus from skin or other surfaces.
- Aqueous iodine has been found to reliably eliminate the cold virus on human skin, however iodine is not acceptable for general use as a virucidal hand treatment because it discolors and dries the skin.
Randomized controlled trials have shown that hand washing using different combinations of cleaning agents resulted in a reduction in the incidence of rhinovirus infections. In two studies at day care facilities, increased handwashing of caregivers reduced the incidence of colds in children by up to 20%. However, scheduled handwashing at an elementary school has been shown to reduce the incidence of all communicable illnesses and gastrointestinal illnesses in particular, but was not shown to prevent respiratory ailments.
Cleaning contaminated surfaces such as coffee cup handles with a mixed alcohol/phenol disinfectant has been shown to almost halve the chance of transmission via direct contact.
Efforts to develop a vaccine against the common cold have been unsuccessful. Common colds are produced by a large variety of rapidly mutating viruses; successful creation of a broadly effective vaccine is highly improbable.
Exposure to cold temperatures and dry weather have been found to facilitate viral infection, explaining why colds and flu are more prevalent in winter outside of tropical areas. Cold weather may make the mucous lining of the respiratory tract more sluggish, taking longer to sweep any inhaled virus particles away. This allows more time for the virus to establish infection and means an individual is infectious (exhaling virus particles) for longer. In humidity above 80%, droplets containing viruses fall out of the air.
However, whilst it creates a better environment for the virus, cold weather itself does not directly cause colds and neither is there evidence supporting the idea that cold weather weakens the cells involved in the immune response.
Management or Treatment
- 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 in all people with cold symptoms.
- Treatment comprises symptomatic support usually via analgesics for fever, headache, sore muscles, and sore throat.
Symptomatic
Treatments that help alleviate symptoms include simple analgesics and antipyretics such as ibuprofen and acetaminophen / paracetamol. Evidence does not show that cough medicine is any more effective than simple analgesics and is not recommended for use in children due to a lack of evidence supporting its effectiveness and the potential for harm.
Symptoms of a runny nose can be reduced by a first generation antihistamine, however it can cause drowsiness and other side effects. Other decongestants such as pseudoephedrine are effective in adults but there is insufficient evidence to support their use in children. Anticholinergics such as Ipratropium nasal spray can reduce the symptoms of runny nose with less side effects.
One study has found chest vapor rub to be effective at providing some symptomatic relief of nocturnal cough, congestion, and sleep difficulty.
Getting plenty of rest, drinking fluids to maintain hydration, and gargling with warm salt water, 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. Saline nasal drops may help alleviate nasal congestion.
Zinc supplements
Zinc deficiency impairs immune function. It has been suggested that zinc may inhibit rhinovirus replication and reduce inflammation. A systematic review by the Cochrane Collaboration, last updated in 2011, concludes that zinc supplements can somewhat reduce the severity and duration of common cold symptoms when taken by otherwise healthy adults within 24 hours of onset of symptoms.
Vitamin C supplements
Vitamin C’s effect on the common cold has been extensively researched. It has not been shown effective in prevention or treatment of the common cold, except in limited circumstances (specifically, individuals exercising vigorously in cold environments). Routine vitamin C supplementation does not reduce the incidence or severity of the common cold in the general population, though it may reduce the duration of illness.
Antibiotics and antivirals
Antibiotics have no effect against viral infections and thus have no effect against the viruses that cause 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 preliminary research has shown benefit.
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