The common cold, or acute viral nasopharyngitis, is a viral infection of the upper respiratory system, which may involve the nose, throat, sinuses, eustachian tubes (connects the ears to the throat), trachea (windpipe), larynx (voice box), and bronchial tubes (airways).
Colds are one of the leading causes of doctor visits and missed days from school and work. According to the Centers for Disease Control and Prevention (CDC), 22 million school days are lost annually in the United States as a result of the common cold. Over the course of a year, people in the United States suffer one billion colds, according to some estimates.
Americans spend about $2.9 billion on over-the-counter (OTC) drugs in addition to $400 million on prescription medicines annually for the symptomatic relief from colds.
It is estimated that the average person contracts more than 50 colds during a lifetime. Anyone can get a cold, although pre-school and grade school children catch them more frequently than adolescents and adults.
One of the main reasons that colds are so common among children is because they are often in close contact with each other in daycare centers and schools. In families with children in school, the number of colds per child can be as high as twelve a year. Also, the thymus gland, which produces immune system cells, is immature in children. Subsequently they have decreased resistance to bacterial and viral infections such as colds.
Adults average about two to four colds annually, although the range varies widely. Women, especially those aged 20-30 years, experience more colds than men, possibly due to closer contact with children. Based on studies, on average, people older than 60 have less 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 rate of colds increases slowly over 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 during the colder months of the year. Cold weather also may make the inside lining of the nose drier and more vulnerable to viral infection.
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