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.
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.
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.
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.
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.
A cold vaccine? The development of a vaccine that could prevent the common
cold has reached an impasse because of the discovery of many different
cold viruses. Each virus carries 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
in one vaccine, or take advantage of the antigenic cross-relationships
that exist, prospects for a vaccine are dim. Evidence that changes occur
in common-cold virus antigens further complicate development of a vaccine.
Such changes occur in some influenza virus antigens and make it necessary
to alter the influenza vaccine each year.
Source: National Institute of Allergy and Infectious Diseases