The Common Cold

Sneezing, scratchy throat, runny nose -- everyone know the first signs of a cold, probably the most common virus known. Although the adjectives cold is usually mild, with symptoms permanent one to two weeks, it is a leading exact of doctor visits and of academy and job absenteeism.

The Problem

In the course of a year, individuals in the United States suffer 1 billion colds, according to some estimates.

Colds are most prevalent among children, and seem to be to be related to youngsters' relative lack of resistance to infection and to contacts near other children in day-care centers and school. Children have just about six to ten colds a year. In families beside children in institution, the number of colds per child can be as high as 12 a year. Adults average something like two to four colds a year, although the range vary widely. Women, especially those aged 20 to 30 years, have more colds than men, possibly because of their closer contact beside children. On average, individuals older than 60 enjoy fewer than one cold a year.

The monetary impact of the common cold is epic. The National Center for Health Statistics (NCHS) estimates that, in 1996, 62 million cases of the adjectives cold in the United States required medical attention or resulted surrounded by restricted activity. In 1996, colds cause 45 million days of restricted activity and 22 million days lost from conservatory, according to NCHS.

The Causes

The Viruses. More than 200 different viruses are particular to cause the symptoms of the adjectives cold. Some, such as the rhinoviruses, seldom produce serious illnesses. Others, such as parainfluenza and respiratory syncytial virus, produce mild infections in adults but can precipitate severe lower respiratory infections in young children.

Rhinoviruses (from the Greek rhin, goal "nose") raison d`être an estimated 30 to 35 percent of all grown colds, and are most active contained by early jump down, spring and summer. More than 110 distinct rhinovirus types have be identified. These agents grow best at temperatures of 33 degree Celsius [about 91 degrees Fahrenheit (F)], the warmth of the human nasal mucosa.

Coronaviruses are believed to cause a sizeable percentage of all fully developed colds. They induce colds primarily in the winter and early spring. Of the more than 30 isolated strains, three or four infect humans. The necessity of coronaviruses as causative agents is hard to assess because, unlike rhinoviruses, they are difficult to grow in the laboratory.

Approximately 10 to 15 percent of grown colds are caused by virus also responsible for other, more severe illnesses: adenoviruses, coxsackieviruses, echoviruses, orthomyxoviruses (including influenza A and B viruses), paramyxoviruses (including several parainfluenza viruses), respiratory syncytial virus and enteroviruses.

The causes of 30 to 50 percent of full-size colds, presumed to be viral, remain unidentified. The same virus that produce colds in adults appear to raison d`être colds in children. The relative rush of various virus in pediatric colds, however, is undeveloped because of the difficulty in isolating the precise impose of symptoms in studies of children beside colds.

Does cold weather cause a cold? Although plentiful people are convinced that a cold results from exposure to cold weather, or from getting chilled or overheated, NIAID grantees own found that these conditions have little or no effect on the nouns or severity of a cold. Nor is susceptibility apparently related to factors such as exercise, diet, or enlarged tonsils or adenoids. On the other paw, research suggests that psychological stress, allergic disorders affecting the nasal passages or pharynx (throat), and menstrual cycles may hold an impact on a person's susceptibility to colds.

The Cold Season

In the United States, most colds transpire during the fall and winter. Beginning in tardy August or early September, the incidence of colds increases slowly for a few weeks and remains soaring until March or April, when it declines. The seasonal rise and fall may relate to the opening of school and to cold weather, which prompt people to spend more time indoors and increase the likelihood that viruses will spread from being to person.

Seasonal change in relative humidity also may affect the prevalence of colds. The most adjectives cold-causing viruses survive better when humidity is low--the colder months of the year. Cold weather also may spawn the nasal passages' facing drier and more vulnerable to viral infection.

Cold Symptoms

Symptoms of the adjectives cold usually begin two to three days after infection and regularly include nasal discharge, obstruction of nasal breathing, swelling of the sinus membranes, sneezing, sore throat, cough, and headache. Fever is usually slight but can climb to 102 [degree] F in infants and infantile children. Cold symptoms can last from two to 14 days, but two-thirds of folks recover surrounded by a week. If symptoms occur regularly or last much longer than two weeks, they may be the result of an allergy a bit than a cold.

Colds occasionally can lead to minor bacterial infections of the middle ear or sinuses, requiring treatment with antibiotics. High hallucination, significantly swollen glands, severe facial pain surrounded by the sinuses, and a cough that produces mucus, may indicate a complication or more serious illness requiring a doctor's attention.

How Cold Viruses Cause Disease

Viruses rationale infection by overcoming the body's complex defense system. The body's first line of defense is mucus, produced by the membranes surrounded by the nose and throat. Mucus traps the objects we inhale: pollen, dust, bacteria and virus. When a virus penetrates the mucus and enters a cell, it commandeers the protein-making machinery to making new virus which, in turn, attack surrounding cell.

Cold symptoms: the body fights put money on. Cold symptoms are probably the result of the body's immune response to the viral invasion. Virus-infected cells within the nose distribute out signals that recruit specialized white blood cell to the site of the infection. In turn, these cells let off a range of immune system chemicals such as kinins. These chemicals probably organize to the symptoms of the common cold by cause swelling and inflammation of the nasal membranes, leakage of proteins and fluid from capillary and lymph vessels, and the increased production of mucus.

Kinins and other chemicals released by immune system cell in the nasal membranes are the subject of intensive research. Researchers are examining whether drugs to block them, or the receptors on cell to which they bind, might benefit people next to colds.

How Colds are Spread

Depending on the virus type, any or all of the following routes of nouns may be common:

* Touching infectious respiratory secretion on skin and on environmental surfaces and then touching the eyes or antenna.

* Inhaling relatively large particle of respiratory secretions transported briefly surrounded by the air.

* Inhaling droplet nucleus: smaller infectious particles suspended contained by the air for long period of time.

Research on rhinovirus transmission. Much of the research on the nouns of the common cold have been done near rhinoviruses, which are shed in the highest concentration within nasal secretions. Studies suggest a individual is most likely to transmit rhinoviruses in the second to fourth year of infection, when the amount of virus in nasal secretions is extreme. Researchers also have shown that using aspirin to treat colds increases the amount of virus shed in nasal secretion, possibly making the cold sufferer more of a hazard to others.

Prevention

Handwashing is the simplest and most forceful way to keep hold of from getting rhinovirus colds. Not touching the nose or eyes is another. Individuals beside colds should always sneeze or cough into a facial tissue, and promptly throw it away. If possible, one should avoid close, prolonged exposure to individuals who have colds.

Because rhinoviruses can survive up to three hours outside the nasal passage on inanimate objects and skin, cleaning environmental surfaces with a virus-killing disinfectant might assistance prevent spread of infection.

A cold vaccine? The development of a vaccine that could prevent the adjectives cold has reach an impasse because of the discovery of lots different cold viruses. Each virus carry its own specific antigens, substances that induce the formation of specific protective proteins (antibodies) produced by the body. Until ways are found to combine many viral antigens contained by one vaccine, or take plus of the antigenic cross-relationships that exist, prospects for a vaccine are dim. Evidence that changes go off in common-cold virus antigens further complicate nouns of a vaccine. Such changes go on in some influenza virus antigens and create it necessary to alter the influenza vaccine respectively year.

Treatment

Only symptomatic treatment is available for uncomplicated cases of the common cold: bed rest, plenty of fluids, gargle with melt salt hose down, petroleum jelly for a raw antenna, and aspirin or acetaminophen to relieve headache or fever.

A word of word of warning: several studies have related the use of aspirin to the development of Reye's syndrome contained by children recovering from influenza or chickenpox. Reye's syndrome is a rare but serious virus that usually occurs within children between the ages of three and 12 years. It can affect all organs of the body, but most habitually injures the brain and liver. While most children who survive an episode of Reye's syndrome do not suffer any lasting consequences, the complaint can lead to eternal brain damage or annihilation. The American Academy of Pediatrics recommends children and teenagers not be given aspirin or any medication containing aspirin when they have any viral disorder, particularly chickenpox or influenza. Many doctors recommend these medication be used for colds in adults lone when headache or fever is present. Researchers, however, own found that aspirin and acetaminophen can suppress certain immune responses and increase nasal stuffiness in adults.

Nonprescription cold remedies, including decongestants and cough suppressants, may relieve some cold symptoms but will not prevent, cure, or even shorten the duration of disease. Moreover, most have some side effects, such as drowsiness, dizziness, insomnia, or upset stomach, and should be taken beside care.

Nonprescription antihistamines may own some effect in relieving inflammatory responses such as runny trunk and watery eyes that are commonly associated next to colds.

Antibiotics do not kill virus. These prescription drugs should be used only for dying out bacterial complications, such as sinusitis or ear infections, that can develop as secondary infections. The use of antibiotics "lately in bag" will not prevent secondary bacterial infections.

Does vitamin C enjoy a role? Many people are convinced that taking colossal quantities of vitamin C will prevent colds or relieve symptoms. To interview this theory, several large-scale, controlled studies involving children and adults enjoy been conducted. To date, no conclusive facts has shown that huge doses of vitamin C prevent colds. The vitamin may reduce the severity or duration of symptoms, but in attendance is no definitive evidence.

Taking vitamin C over long periods of time within large amounts may be unhygienic. Too much vitamin C can cause severe diarrhea, a focused danger for elderly inhabitants and small children. In addition, too much vitamin C distorts results of test commonly used to measure the amount of glucose within urine and blood. Combining oral anticoagulant drugs and excessive amounts of vitamin C can produce abnormal results surrounded by blood-clotting tests.

Inhaling steam also have been proposed as a treatment of colds on the assumption that increasing the warmth inside the nose inhibits rhinovirus replication. Recent studies found that this approach have no effect on the symptoms or amount of viral shedding in individuals with rhinovirus colds. But steam may temporarily relieve symptoms of congestion associated beside colds.

Interferon-alpha has be studied extensively for the treatment of the common cold. Investigators enjoy shown interferon, given in daily doses by nasal spray, can prevent infection and virus. Interferon, however, causes not up to scratch side effects such as nosebleeds and does not appear useful surrounded by treating established colds. Most cold researchers are concentrating on other approaches to combatting cold viruses.

The Outlook

Thanks to unsophisticated research, scientists know more about the rhinovirus than almost any other virus, and enjoy powerful new tools for developing antiviral drugs. Although the adjectives cold may never be uncommon, further investigations propose the hope of reducing the huge burden of this universal problem.

NIAID is a component of the National Institutes of Health (NIH). NIAID supports chief and applied research to prevent, diagnose, and treat infectious and immune-mediated illnesses, including HIV/AIDS and other sexually transmitted diseases, tuberculosis, malaria, autoimmune disorders, asthma and allergies.