The common cold is a viral infectious disease
of the upper respiratory tract which primarily affects the nose. Symptoms include coughing,
sore throat, runny nose, sneezing, and fever which usually resolve in seven to ten days,
with some symptoms lasting up to three weeks. Well over 200 virus strains are implicated
in the cause of the common cold; the rhinoviruses are the most common.
Upper respiratory tract infections are loosely divided by the areas they affect, with the
common cold primarily affecting the nose, the throat, and the sinuses, occasionally
involving either or both eyes via conjunctivitis. Symptoms are mostly due to the body’s immune
response to the infection rather than to tissue destruction by the viruses themselves. The
primary method of prevention is by hand washing with some evidence to support the effectiveness
of wearing face masks. The common cold may occasionally lead to pneumonia, either viral
pneumonia or secondary bacterial pneumonia. No cure for the common cold exists, but the
symptoms can be treated. It is the most frequent infectious disease in humans with the average
adult getting two to three colds a year and the average child getting between six and
twelve. These infections have been with humanity since antiquity. Signs and symptoms
The typical symptoms of a cold include cough, runny nose, nasal congestion and a sore throat,
sometimes accompanied by muscle ache, fatigue, headache, and loss of appetite. A sore throat
is present in about 40% of the cases and a cough in about 50%, while muscle ache occurs
in about half. In adults, a fever is generally not present but it is common in infants and
young children. The cough is usually mild compared to that accompanying influenza. While
a cough and a fever indicate a higher likelihood of influenza in adults, a great deal of similarity
exists between these two conditions. A number of the viruses that cause the common cold
may also result in asymptomatic infections. The color of the sputum or nasal secretion
may vary from clear to yellow to green and does not indicate the class of agent causing
the infection. Progression
A cold usually begins with fatigue, a feeling of being chilled, sneezing and a headache,
followed in a couple of days by a runny nose and cough. Symptoms may begin within 16 hours
of exposure and typically peak two to four days after onset. They usually resolve in
seven to ten days but some can last for up to three weeks. The average duration of cough
is 18 days and in some cases people develop a post-viral cough which can linger after
the infection is gone. In children, the cough lasts for more than ten days in 35–40% of
the cases and continues for more than 25 days in 10%.
Cause Virology The common cold is a viral infection of the
upper respiratory tract. The most commonly implicated virus is a rhinovirus, a type of
picornavirus with 99 known serotypes. Others include: human coronavirus, influenza viruses,
adenoviruses, human parainfluenza viruses, human respiratory syncytial virus, enteroviruses
other than rhinoviruses, and metapneumovirus. Frequently more than one virus is present.
In total over 200 different viral types are associated with colds.
Transmission The common cold virus is typically transmitted
via airborne droplets, direct contact with infected nasal secretions, or fomites. Which
of these routes is of primary importance has not been determined; however, hand-to-hand
and hand-to-surface-to-hand contact seems of more importance than transmission via aerosols.
The viruses may survive for prolonged periods in the environment and can be picked up by
people’s hands and subsequently carried to their eyes or nose where infection occurs.
Transmission is common in daycare and at school due to the proximity of many children with
little immunity and frequently poor hygiene. These infections are then brought home to
other members of the family. There is no evidence that recirculated air during commercial flight
is a method of transmission. However, people sitting in close proximity appear at greater
risk. Rhinovirus-caused colds are most infectious during the first three days of symptoms; they
are much less infectious afterwards. Weather
The traditional folk theory is that a cold can be “caught” by prolonged exposure to cold
weather such as rain or winter conditions, which is how the disease got its name. Some
of the viruses that cause the common colds are seasonal, occurring more frequently during
cold or wet weather. The reason for the seasonality has not been conclusively determined. This
may occur due to cold induced changes in the respiratory system, decreased immune response,
and low humidity increasing viral transmission rates, perhaps due to dry air allowing small
viral droplets to disperse farther and stay in the air longer. It may be due to social
factors, such as people spending more time indoors, near an infected person, and specifically
children at school. There is some controversy over the role of low body temperature as a
risk factor for the common cold; the majority of the evidence suggests that it may result
in greater susceptibility to infection. Other
Herd immunity, generated from previous exposure to cold viruses, plays an important role in
limiting viral spread, as seen with younger populations that have greater rates of respiratory
infections. Poor immune function is also a risk factor for disease. Insufficient sleep
and malnutrition have been associated with a greater risk of developing infection following
rhinovirus exposure; this is believed to be due to their effects on immune function. Breast
feeding decreases the risk of acute otitis media and lower respiratory tract infections
among other diseases and it is recommended that breast feeding be continued when an infant
has a cold. In the developed world breast feeding may not however be protective against
the common cold in and of itself. Pathophysiology The symptoms of the common cold are believed
to be primarily related to the immune response to the virus. The mechanism of this immune
response is virus specific. For example, the rhinovirus is typically acquired by direct
contact; it binds to human ICAM-1 receptors through unknown mechanisms to trigger the
release of inflammatory mediators. These inflammatory mediators then produce the symptoms. It does
not generally cause damage to the nasal epithelium. The respiratory syncytial virus on the other
hand is contracted by both direct contact and airborne droplets. It then replicates
in the nose and throat before frequently spreading to the lower respiratory tract. RSV does cause
epithelium damage. Human parainfluenza virus typically results in inflammation of the nose,
throat, and bronchi. In young children when it affects the trachea it may produce the
symptoms of croup due to the small size of their airway.
Diagnosis The distinction between different viral upper
respiratory tract infections is loosely based on the location of symptoms with the common
cold affecting primarily the nose, pharyngitis the throat, and bronchitis the lungs. However
there can be significant overlap and multiple areas can be affected. The common cold is
frequently defined as nasal inflammation with varying amount of throat inflammation. Self-diagnosis
is frequent. Isolation of the actual viral agent involved is rarely performed, and it
is generally not possible to identify the virus type through symptoms.
Prevention The only possibly useful ways to reduce the
spread of cold viruses are physical measures such as hand washing and face masks; in the
healthcare environment, gowns and disposable gloves are also used. Isolation, e.g. quarantine,
is not possible as the disease is so widespread and symptoms are non-specific. Vaccination
has proved difficult as there are so many viruses involved and they mutate rapidly.
Creation of a broadly effective vaccine is thus highly improbable.
Regular hand washing appears to be effective in reducing the transmission of cold viruses,
especially among children. Whether the addition of antivirals or antibacterials to normal
hand washing provides greater benefit is unknown. Wearing face masks when around people who
are infected may be beneficial; however, there is insufficient evidence for maintaining a
greater social distance. Zinc supplements may help to reduce the prevalence of colds.
Routine vitamin C supplements do not reduce the risk or severity of the common cold, though
they may reduce its duration. Management No medications or herbal remedies have been
conclusively demonstrated to shorten the duration of infection. Treatment thus comprises symptomatic
relief. Getting plenty of rest, drinking fluids to maintain hydration, and gargling with warm
salt water, are reasonable conservative measures. Much of the benefit from treatment is however
attributed to the placebo effect. Symptomatic
Treatments that help alleviate symptoms include simple analgesics and antipyretics such as
ibuprofen and acetaminophen/paracetamol. Evidence does not show that cough medicines are any
more effective than simple analgesics and they are not recommended for use in children
due to a lack of evidence supporting effectiveness and the potential for harm. In 2009, Canada
restricted the use of over-the-counter cough and cold medication in children six years
and under due to concerns regarding risks and unproven benefits. In adults there is
insufficient evidence to support the use of cough medications. The misuse of dextromethorphan
has led to its ban in a number of countries. In adults the symptoms of a runny nose can
be reduced by first-generation antihistamines; however, these sometimes have adverse effects
such as drowsiness. Other decongestants such as pseudoephedrine are also effective in adults.
Ipratropium nasal spray may reduce the symptoms of a runny nose but has little effect on stuffiness.
Second-generation antihistamines however do not appear to be effective.
Due to lack of studies, it is not known whether increased fluid intake improves symptoms or
shortens respiratory illness and a similar lack of data exists for the use of heated
humidified air. One study has found chest vapor rub to provide some relief of nocturnal
cough, congestion, and sleep difficulty. Antibiotics and antivirals
Antibiotics have no effect against viral infections and thus have no effect against the viruses
that cause the common cold. Due to their side effects, antibiotics cause overall harm, but
are still frequently prescribed. Some of the reasons that antibiotics are so commonly prescribed
include people’s expectations for them, physicians’ desire to help, and the difficulty in excluding
complications that may be amenable to antibiotics. There are no effective antiviral drugs for
the common cold even though some preliminary research has shown benefits.
Alternative medicine While there are many alternative treatments
used for the common cold, there is insufficient scientific evidence to support the use of
most. As of 2010 there is insufficient evidence to recommend for or against either honey or
nasal irrigation. Zinc has been used to treat symptoms, with studies suggesting that zinc,
if taken within 24 hours of the onset of symptoms, reduces the duration and severity
of the common cold in otherwise healthy people. Due to wide differences between the studies,
further research may be needed to determine how and when zinc may be effective. Whereas
the zinc lozenges may produce side effects, there is only a weak rationale for physicians
to recommend zinc for the treatment of the common cold. Vitamin C’s effect on the common
cold, while extensively researched, is disappointing, except in limited circumstances, specifically,
individuals exercising vigorously in cold environments. There is no firm evidence that
Echinacea products provide any meaningful benefit in treating or preventing colds. It
is unknown if garlic is effective. A single trial of vitamin D did not find benefit.
Prognosis The common cold is generally mild and self-limiting
with most symptoms generally improving in a week. Half of cases go away in 10 days
and 90% in 15 days. Severe complications, if they occur, are usually in the very old,
the very young, or those who are immunosuppressed. Secondary bacterial infections may occur resulting
in sinusitis, pharyngitis, or an ear infection. It is estimated that sinusitis occurs in 8%
and an ear infection in 30% of cases. Epidemiology
The common cold is the most common human disease, and affects people all over the globe. Adults
typically have two to five infections annually and children may have six to ten colds a year.
Rates of symptomatic infections increase in the elderly due to a worsening immune system.
Native Americans and Inuit are more likely to be infected with colds and develop complications
such as otitis media more often than Caucasians. This may be explained by issues such as poverty
and overcrowding rather than by ethnicity. History While the cause of the common cold has only
been identified since the 1950s the disease has been with humanity since antiquity. Its
symptoms and treatment are described in the Egyptian Ebers papyrus, the oldest existing
medical text, written before the 16th century BCE. The name “cold” came into use in the
16th century, due to the similarity between its symptoms and those of exposure to cold
weather. In the United Kingdom, the Common Cold Unit
was set up by the Medical Research Council in 1946 and it was here that the rhinovirus
was discovered in 1956. 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.
Society and culture The economic impact of the common cold is
not well understood in much of the world. In the United States, the common cold leads
to 75–100 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 people who
saw a doctor received an antibiotic prescription, which has implications for antibiotic resistance.
An estimated 22–189 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. This accounts for 40% of
time lost from work in the United States. Research directions
A number of antivirals have been tested for effectiveness in the common cold; however
as of 2009 none have been both found effective and licensed for use. There are ongoing trials
of the anti-viral drug pleconaril which shows promise against picornaviruses as well as
trials of BTA-798. The oral form of pleconaril had safety issues and an aerosol form is being
studied. DRACO, a broad-spectrum antiviral therapy
being developed at the Massachusetts Institute of Technology, has shown preliminary effectiveness
in treating rhinovirus, as well as a number of other infectious viruses.
Researchers from the University of Maryland School of Medicine in Baltimore and the University
of Wisconsin–Madison have sequenced the genome for all known human rhinovirus strains.
References Notes External links Common cold at DMOZ