What Is It?
The common cold, also called viral rhinitis, is one of the most common infectious diseases in humans. Though the infection is usually mild and improves without treatment, it causes widespread illness and discomfort, resulting in nearly 26 million days of missed school and 23 million days of work absence annually in the United States. The average American experiences one to three colds per year.

The common cold is an upper respiratory infection that is caused by a wide variety of viruses. More than 200 viral agents have been identified. The biggest offender, called the rhinovirus (which causes up to 40 percent of colds), has 100 distinct types. Other important upper respiratory viruses include coronaviruses, adenovirus and respiratory syncytial virus (RSV). This incredible diversity has made the development of a vaccine for the common cold almost impossible.

Rhinoviruses, the most likely agents to cause colds, have a well-established seasonal pattern, peaking in the early fall and spring. Other viruses tend to cause winter colds, which are usually more debilitating. Despite popular belief, cold temperatures do not appear to increase either the incidence or severity of the common cold. There is no evidence that exposure to cold or rainy weather makes you more likely to catch a cold.

Symptoms
The common cold causes a constellation of symptoms that usually are easily recognized by patients and doctors alike. About 50 percent of patients will develop a sore throat, which is often the first manifestation of illness since it can occur as early as 10 hours after infection. This is rapidly followed by the most common symptoms of the common cold — congested nasal and sinus passages, a runny nose and sneezing. Hoarseness and cough are less likely to occur, but they may be more persistent than the other symptoms, sometimes lasting several weeks. However, high fevers and chills rarely occur.

Diagnosis
Most patients diagnose the common cold by the typical symptoms of runny nose, congestion and sneezing and rarely consult medical attention. When health care providers are consulted, they attempt to rule out more serious illnesses or complications such as bacterial sinusitis and pneumonia.

Your physician will ask about the history of your symptoms to make sure you don't have severe sinus pain, shortness of breath, wheezing or high fevers. He or she usually will perform a careful physical examination of your upper respiratory tract, including your throat and the lymph nodes in your neck, and may also listen to your lungs with a stethoscope.

Blood tests and X-rays rarely are indicated to diagnose the common cold. If your doctor orders these tests, it is usually to rule out a more serious illness.

Expected Duration
Symptoms typically peak on the second, third or fourth days of infection and the median duration of symptoms is one week. People are most infectious (likely to pass the cold onto others) during the first 24 hours of the illness and they will remain infectious for as long as the symptoms persist. Up to 25 percent of people may have persistent symptoms, such as a nagging cough that can last for several weeks. A small number of people may develop another illness, such as bacterial infections of the middle ear or the sinuses and others may develop exacerbations of asthma or chronic bronchitis. These patients may have a prolonged illness.

Prevention
Colds most often are spread to people in close contact. Usually about half of the family members of an infected person will become ill. Frequent transmission also occurs at school and daycare.

The common cold is most often transmitted by direct contact with the respiratory secretions of someone who is infected, usually by hand-to-hand contact. The infected respiratory secretions are passed from one person's hand to another. The second person then touches his or her eyes or rubs his or her nose, spreading the virus there, where it can cross the delicate membranes and cause infection. It is also possible to become infected by touching a surface, such as a tabletop or doorknob, that was recently touched by an infected person and then touching your eyes or nose. Viruses can survive on such surfaces for up to three hours.

Therefore, frequent handwashing, careful disposal of all used tissues and avoidance of rubbing your eyes and nose are extremely important to prevent transmission of the common cold. These viruses can also be spread by inhaling particles from the air after an infected person has coughed or sneezed; if possible, you should avoid close, prolonged exposure to people who have colds.

Treatment
While medical therapies can improve the symptoms of the common cold, they do not prevent, cure or shorten the duration of the illness. It's important to drink adequate fluids, get plenty of rest and treat your symptoms to keep yourself as comfortable as possible. Gargling warm salt water can soothe a sore throat, inhaling steam may temporarily improve nasal congestion, and over-the-counter cold remedies, including decongestants and cough suppressants, will relieve congestion and cough. Antihistamines may improve the symptoms of runny nose and watery eyes, but they should be used with care since over-the-counter formulations cause sedation. It is important to keep in mind that antibiotics do not cure the common cold, nor do they decrease the duration of symptoms. Vitamin C, zinc and echinacea (a frequently used herbal therapy) have been widely rumored to decrease the duration of symptoms and the likelihood of developing the common cold, but no conclusive data has demonstrated that this is the case.

When To Call A Professional
Though the common cold usually causes a mild illness and most people do not seek medical attention, a small number of people can develop bacterial infections of the middle ear, sinuses or lungs. If you develop high fevers, severe pain over your sinuses, severe wheezing or shortness of breath, you should see your physician to be sure that you don't have a more serious illness, such as pneumonia, bacterial sinusitis or a middle ear infection.

Prognosis
The common cold usually causes a mild, self-limited infection that improves on its own within a week. However, some people may have symptoms that last for several weeks and a small number of patients may develop bacterial infections of the ear, sinuses or lungs following the common cold.

Souce: The Centers for Disease Control and Prevention (CDC)