Common cold

Common cold
Specialty	Family medicine, infectious diseases, otorhinolaryngology

Acute viral rhinopharyngitis, or acute coryza, usually known as the common cold, is a highly contagious, viral infectious disease of the upper respiratory system, primarily caused by picornaviruses (including rhinoviruses) or coronaviruses.

Common symptoms are sore throat, runny nose, nasal congestion, sneezing and coughing; sometimes accompanied by 'pink eye', muscle aches, fatigue, malaise, headaches, muscle weakness, uncontrollable shivering, and loss of appetite. Fever and extreme exhaustion are rare during a cold and are more usual in influenza. The symptoms of a cold usually resolve after about one week, but can last up to two. Symptoms may be more severe in infants and young children. 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. Though some alternative treatments such as Vitamin C megadosage, echinacea, and zinc have been proposed, none of them have been shown to decrease the duration of the illness, and thus none of them are approved by the Food and Drug Administration or European Medicines Agency. To prevent infection, washing or disinfecting hands has been found effective, as this minimizes person-to-person transmission of the virus.

Symptoms

After initial infection, the viral replication cycle begins within 8 to 12 hours. Symptoms can occur shortly thereafter, and usually begin within 2 to 5 days after infection, although occasionally in as little as 10 hours after infection. The first indication of a cold is often a sore or scratchy throat. Other common symptoms are runny nose, congestion, sneezing and cough. These are sometimes accompanied by muscle aches, fatigue, malaise, headache, weakness, or loss of appetite. The symptoms usually resolves spontaneously in 7 to 10 days but some can last for up to three weeks. Symptoms may be more severe in infants, young children and tobacco users/smokers, and may include fever and hives.

Cause

The common cold is most often caused by infection with one of the more than 250 serotypes of rhinovirus, a type of picornavirus. Other viruses causing colds are coronavirus, human parainfluenza viruses, human respiratory syncytial virus, adenoviruses, enteroviruses, or metapneumovirus. 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 less 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.

Exposure to cold weather

Exposure to cold weather has not been proven to increase the likelihood of "catching" a cold

An ancient myth still common today claims that a cold can be "caught" by prolonged exposure to cold weather such as rain or winter conditions. 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 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 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.

Pathophysiology

The common cold is a disease of the upper respiratory tract

The common cold virus is transmitted between people by one of two mechanisms: 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.

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.

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.

Treatment

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

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 often is given via symptomatic supportive options, maximizing the comfort of the patient, and limiting complications and harmful sequelae.

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.

Conservative management

The National Institute of Allergy and Infectious Diseases suggests getting plenty of rest, drinking fluids to maintain hydration, gargling with warm salt water, using cough drops, throat sprays, or over-the-counter pain or cold medicines. Saline nasal drops may help alleviate congestion.

Treatment that may help alleviate symptoms include: analgesics, decongestants, and cough suppressants.

First-generation anti-histamines such as brompheniramine, chlorpheniramine, diphenhydramine and clemastine (which reduce mucus gland secretion and thus combat blocked/runny noses but also may make the user drowsy). Second-generation anti-histamines do not have a useful effect on colds.

Antibiotics

Antibiotics only target bacteria and thus do not have any beneficial effect against the common cold.

Antivirals

There are no approved antiviral drugs for the common cold.

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.

Alternative treatments

Main article: Alternative treatments used for the common cold

Many herbal remedies have been suggested to treat the common cold. None, however, has been shown to be effective.

Prevention

The best way to avoid a cold is to avoid close contact with existing sufferers; to wash hands thoroughly and regularly; and to avoid touching the mouth and face. Anti-bacterial soaps have no effect on the cold virus; it is the mechanical action of hand washing with the soap that removes the virus particles.

In 2002, the Centers for Disease Control and Prevention recommended alcohol-based hand gels as an effective method for reducing infectious viruses on the hands of health care workers. As with hand washing with soap and water, alcohol gels provide no 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.

Epidemiology

Upper respiratory tract infections are the most common infectious diseases among adults and teens, 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.

Economic cost

An American poster from World War II describing the cost of the common cold

United States

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.

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.

History

"Definition of a Cold." Benjamin Franklin's notes for a paper he intended to write on the common cold.

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. 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

Main article: 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.

See also

• Vitamin C and the common cold