Colds

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%[2]), 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

People with the lowest blood vitamin D levels reported having significantly more recent colds or cases of the flu. The risks were even higher for those with chronic respiratory disorders, such as asthma and emphysema. However, this statistical correlation does not prove that low levels cause increased susceptibility to viral infections and the authors stress that the study's results need to be confirmed in clinical trials before vitamin D can be recommended to prevent colds and flu.

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; however, cold environments do tend to slow down the immune system.

With respect to the causation of cold-like symptoms, researchers at the Common Cold Centre at Cardiff University 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 reported cold symptoms 4 or 5 days after the chilling. In particular, 13 of the 90 chilled subjects reported having a cold 4 or 5 days after the study, in contrast to 5 of the 90 control subjects reporting the same (p-value was 0.047). The study concluded that the onset of common cold symptoms can be caused by acute chilling of the feet. One possible explanation postulated by past researchers is that, during the cold season, "many people are mildly infected but show no symptoms," but "if they become chilled, this causes a pronounced constriction of the blood vessels in the nose and shuts off the warm blood that supplies the white cells that fight infection. Although the chilled subject believes they have 'caught a cold' what has, in fact, happened is that the dormant infection has taken hold.". However, this explanation has not been scientifically verified.

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.

Humidity

Humidity is also believed to play a role in viral transmission. One theory is that dry air causes evaporation of water and smaller viral droplets that dispurse farther and stay in the air longer

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 has been unsuccessful. This is due to a number of reasons including a large variety of viruses and the fact that they mutate rapidly. Many thus believe that successful immunization is highly improbable.

Management

There are currently no medications or herbal remedies which have been conclusively demonstrated to shorten the duration of illness. Treatment comprises 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 and antipyretics such as ibuprofen and acetaminophen / paracetamol.

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 preliminary research has shown benefit.

Alternative treatments

Many alternative treatments are used to treat the common cold. However, there is insufficient scientific evidence to support the use of any alternative medicine treatments.

Honey may be an effective treatment of cough. Buckwheat honey given before bedtime provided better cough relief at night and improved sleep difficulty in children more than no treatment or dextromethorphan.

A 1999 Cochrane review found the evidence of benefit from zinc in the common cold is inconclusive. A 2003 review however concluded supported the value of zinc in reducing the duration and severity of symptoms of the common cold when administered within 24 hours of the onset of common cold symptoms. Nasally applied zinc gels may lead to loss of smell. The FDA therefore discourages their use.

A review of sixteen trials of echinacea was done by the Cochrane Collaboration in 2006 and found mixed results. All three trials that looked at prevention were negative. Comparisons of echinacea as treatment found a significant effect in nine trials, a trend in one, and no difference in six trials. The authors state in their conclusion: "Echinacea preparations tested in clinical trials differ greatly. There is some evidence that preparations based on the aerial parts of Echinacea purpurea might be effective for the early treatment of colds in adults but results are not fully consistent. Beneficial effects of other Echinacea preparations, and for preventative purposes might exist but have not been shown in independently replicated, rigorous randomized trials.". A review in 2007 found an overall benefit from echinacea for the common cold.

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.

While a number of Chinese herbs and plants have been purported to ease cold symptoms, including ginger, garlic, hyssop, mullein, and others, scientific studies have either not been done or have been found inconclusive.

Prognosis

The common cold is generally mild and self-limiting.