Health & Nutrition
The Common Cold
Problem
• Causes
• Cold Season
• Symptoms
• How Cold Viruses Cause Disease
• How Colds are Spread
• Prevention
• Treatment
Sneezing, scratchy throat, runny nose - everyone knows the first signs of a
cold, probably the most common illness known. Although the common cold is
usually mild, with symptoms lasting one to two weeks, it is a leading cause of
doctor visits and of school 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 related to youngsters' relative lack of resistance to infection and
to contacts with other children in day-care centers and schools. Children have
about six to ten colds a year. In families with children in school, the number
of colds per child can be as high as 12 a year. Adults average about two to four
colds a year, although the range varies widely. Women, especially those aged 20
to 30 years, have more colds than men, possibly because of their closer contact
with children. On average, individuals older than 60 have fewer than one cold a
year.
The economic impact of the common cold is enormous. The National Center for
Health Statistics (NCHS) estimates that, in 1996, 62 million cases of the common
cold in the United States required medical attention or resulted in restricted
activity. In 1996, colds caused 45 million days of restricted activity and 22
million days lost from school, according to NCHS.
The Causes
The Viruses. More than 200 different viruses are known to cause the symptoms
of the common 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, meaning "nose") cause an
estimated 30 to 35 percent of all adult colds, and are most active in early
fall, spring and summer. More than 110 distinct rhinovirus types have been
identified. These agents grow best at temperatures of 33 degrees Celsius [about
91 degrees Fahrenheit (F)], the temperature of the human nasal mucosa.
Coronaviruses are believed to cause a large percentage of all adult colds.
They induce colds primarily in the winter and early spring. Of the more than 30
isolated strains, three or four infect humans. The importance 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 adult colds are caused by viruses 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 adult colds, presumed to be viral, remain
unidentified. The same viruses that produce colds in adults appear to cause
colds in children. The relative importance of various viruses in pediatric
colds, however, is unclear because of the difficulty in isolating the precise
cause of symptoms in studies of children with colds.
Does cold weather cause a cold? Although many people are convinced that a
cold results from exposure to cold weather, or from getting chilled or
overheated, researchers have found that these conditions have little or no
effect on the development or severity of a cold. Nor is susceptibility
apparently related to factors such as exercise, diet, or enlarged tonsils or
adenoids. On the other hand, research suggests that psychological stress,
allergic disorders affecting the nasal passages or pharynx (throat), and
menstrual cycles may have an impact on a person's susceptibility to colds.
The Cold Season
In the United States, most colds occur during the fall and winter. Beginning
in late August or early September, the incidence of colds increases slowly for a
few weeks and remains high until March or April, when it declines. The seasonal
variation may relate to the opening of schools and to cold weather, which prompt
people to spend more time indoors and increase the chances that viruses will
spread from person to person.
Seasonal changes in relative humidity also may affect the prevalence of
colds. The most common cold-causing viruses survive better when humidity is
low-the colder months of the year. Cold weather also may make the nasal
passages' lining drier and more vulnerable to viral infection.
Cold Symptoms
Symptoms of the common cold usually begin two to three days after infection
and often 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 102o F in infants and young children. Cold
symptoms can last from two to 14 days, but two-thirds of people recover in a
week. If symptoms occur often or last much longer than two weeks, they may be
the result of an allergy rather than a cold.
Colds occasionally can lead to secondary bacterial infections of the middle
ear or sinuses, requiring treatment with antibiotics. High fever, significantly
swollen glands, severe facial pain in 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 cause infection by overcoming the body's complex defense system. The
body's first line of defense is mucus, produced by the membranes in the nose and
throat. Mucus traps the material we inhale: pollen, dust, bacteria and viruses.
When a virus penetrates the mucus and enters a cell, it commandeers the
protein-making machinery to manufacture new viruses which, in turn, attack
surrounding cells.
Cold symptoms: the body fights back. Cold symptoms are probably the result of
the body's immune response to the viral invasion. Virus-infected cells in the
nose send out signals that recruit specialized white blood cells to the site of
the infection. In turn, these cells emit a range of immune system chemicals such
as kinins. These chemicals probably lead to the symptoms of the common cold by
causing swelling and inflammation of the nasal membranes, leakage of proteins
and fluid from capillaries and lymph vessels, and the increased production of
mucus.
Kinins and other chemicals released by immune system cells in the nasal
membranes are the subject of intensive research. Researchers are examining
whether drugs to block them, or the receptors on cells to which they bind, might
benefit people with colds.
How Colds are Spread
Depending on the virus type, any or all of the following routes of
transmission may be common:
Touching infectious respiratory secretions on skin and on environmental
surfaces and then touching the eyes or nose.
Inhaling relatively large particles of respiratory secretions transported
briefly in the air. Inhaling droplet nuclei: smaller infectious particles
suspended in the air for long periods of time.
Research on rhinovirus transmission. Much of the research on the transmission
of the common cold has been done with rhinoviruses, which are shed in the
highest concentration in nasal secretions.
Studies suggest a person is most likely to transmit rhinoviruses in the
second to fourth day of infection, when the amount of virus in nasal secretions
is highest. Researchers also have shown that using aspirin to treat colds
increases the amount of virus shed in nasal secretions, possibly making the cold
sufferer more of a hazard to others.
Prevention
Handwashing is the simplest and most effective way to keep from getting
rhinovirus colds. Not touching the nose or eyes is another. Individuals with
colds should always sneeze or cough into a facial tissue, and promptly throw it
away. If possible, one should avoid close, prolonged exposure to persons who
have colds.
Because rhinoviruses can survive up to three hours outside the nasal passages
on inanimate objects and skin, cleaning environmental surfaces with a
virus-killing disinfectant might help prevent spread of infection.
Treatment
Only symptomatic treatment is available for uncomplicated cases of the common
cold: bed rest, plenty of fluids, gargling with warm salt water, petroleum jelly
for a raw nose, and aspirin or acetaminophen to relieve headache or fever.
A word of caution: several studies have linked the use of aspirin to the
development of Reye's syndrome in children recovering from influenza or
chickenpox. Reye's syndrome is a rare but serious illness that usually occurs in
children between the ages of three and 12 years. It can affect all organs of the
body, but most often injures the brain and liver. While most children who
survive an episode of Reye's syndrome do not suffer any lasting consequences,
the illness can lead to permanent brain damage or death. The American Academy of
Pediatrics recommends children and teenagers not be given aspirin or any
medications containing aspirin when they have any viral illness, particularly
chickenpox or influenza. Many doctors recommend these medications be used for
colds in adults only when headache or fever is present. Researchers, however,
have 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 illness. Moreover, most have some side effects, such as
drowsiness, dizziness, insomnia, or upset stomach, and should be taken with
care.
Nonprescription antihistamines may have some effect in relieving inflammatory
responses such as runny nose and watery eyes that are commonly associated with
colds.
Antibiotics do not kill viruses. These prescription drugs should be used only
for rare bacterial complications, such as sinusitis or ear infections, that can
develop as secondary infections. The use of antibiotics "just in case"
will not prevent secondary bacterial infections.
Does vitamin C have a role? Many people are convinced that taking large
quantities of vitamin C will prevent colds or relieve symptoms. To test this
theory, several large-scale, controlled studies involving children and adults
have been conducted. To date, no conclusive data has shown that large doses of
vitamin C prevent colds. The vitamin may reduce the severity or duration of
symptoms, but there is no definitive evidence.
Taking vitamin C over long periods of time in large amounts may be harmful.
Too much vitamin C can cause severe diarrhea, a particular danger for elderly
people and small children. In addition, too much vitamin C distorts results of
tests commonly used to measure the amount of glucose in urine and blood.
Combining oral anticoagulant drugs and excessive amounts of vitamin C can
produce abnormal results in blood-clotting tests.
Inhaling steam also has been proposed as a treatment of colds on the
assumption that increasing the temperature inside the nose inhibits rhinovirus
replication. Recent studies found that this approach had no effect on the
symptoms or amount of viral shedding in individuals with rhinovirus colds. But
steam may temporarily relieve symptoms of congestion associated with colds.
Interferon-alpha has been studied extensively for the treatment of the common
cold. Investigators have shown interferon, given in daily doses by nasal spray,
can prevent infection and illness. Interferon, however, causes unacceptable side
effects such as nosebleeds and does not appear useful in treating established
colds.
National Institute of Allergy and Infectious Diseases
National Institutes of Health
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