Colds are viral infections of the nose and throat. Colds can go on to involve the sinuses, ears, larynx (vocal cords), trachea and bronchi directly or through secondary effects. The presence of the virus causes inflammation of membrane linings, so that there is swelling with obstruction (stuffiness) and increased mucous secretions. Colds are the most common type of respiratory infection; they are usually mild illnesses that naturally come to an end, only occasionally leading to further problems.
There are many viruses that can cause colds, sometimes seasonally and sometimes in epidemics. Up to 50% of colds are caused by one of the more than 100 rhinoviruses (rhino = nose). Other viruses that cause colds are the coronaviruses, adenoviruses, respiratory syncytial virus and parainfluenza viruses. Some of these viruses are capable of causing more severe disease in very young infants (such as pneumonia), but only cause colds in older children and adults.
A person with a cold is usually contagious from 24 hours before the beginning of symptoms and as long as the symptoms last, which is usually about a week. Rhinoviruses are most often spread by direct contact with infected secretions, e.g. touching objects such as handkerchiefs, door-knobs or eating utensils that a person with a cold has touched before, and then touching one's nose or mouth. Rhinoviruses are less often spread by airborne particles, such as when an infected person sneezes.
Your immune system responds by attacking the virus with white blood cells. If your immune system cannot recognise the virus from a previous infection, the response is "non-specific", meaning your body produces as many white blood cells as possible and circulates them to the infected sites. White cells produce chemicals to kill virus-infected cells, and this is what causes the nasal inflammation and swelling, increased mucous secretions and the general feeling of achiness. Once infected with a specific cold virus, the body develops immunity to it in the form of "memory white cells" and antibodies, which will control the virus quickly in the event that it is encountered again. Immunity will prevent another cold being caused by the same rhinovirus for some months at least, but does not protect against others.
One to three days after exposure, the illness begins with sore throat, discomfort in the nose and sneezing, soon followed by a running nose and unwellness.
Colds are typically not associated with high fever, which should not reach more than 38.5°C. Headache, tiredness and muscle aches can occur. The watery secretions thicken during the first day and become yellow or green in colour, due to the presence of white cells. This is the time when bacterial infection might worsen the illness. Since the lining of the upper airways is now inflamed, it is easier for normal bacteria inhabiting the surfaces to invade. In addition, blockage of the narrow air passageways from the nose to the sinuses allows accumulation of mucous secretions in the sinuses in which bacteria can multiply. Similarly, the eustachian tube from the throat to the middle ear can close up, leading to middle ear infection (otitis media). In children the virus itself can cause middle ear and sinus infections.
A post-nasal drip, where infected secretions run down the back of the throat, (often causing an uncomfortable burning sensation) is not an uncommon sequel of a cold. Laryngitis and inflammation of the trachea can be consequences of the variable extension of the viral and/or bacterial infection into the upper airways. Inflammation and swelling of the vocal cords so that they no longer move properly is what causes the loss of voice in laryngitis. Further progression down the airways leads to bronchitis. Coughing is due to the irritation of the linings of these airways. Coughing is often worse in bed at night or on rising in the morning due to movement of secretions in response to a change in position. If other symptoms are improving, and the cough does not persist and is not productive, it is not a cause for concern.
Colds can also worsen other underlying illnesses. Chronic bronchitis due to for example smoking can flare up with increased coughing and sputum production, and the spasm of the airways in asthmatics can be significantly worsened, bringing on an sudden asthmatic episode.
When no complications occur, a cold should be over in four to 10 days.
Colds can occur during any season and can affect anyone. Children get colds far more often than adults do. This may be due to the fact that they touch their faces and noses after touching other objects a great deal, and also because they haven't been exposed to as many viruses and have not had time to build up the kind of immunity that adults have.
Predisposing factors are not really known. Chilling the body surface does not by itself induce colds, and the ease of acquiring one does not correlate clearly with fitness, nutritional health or upper airway abnormalities (such as enlarged tonsils). However, contracting a cold virus may be facilitated by fatigue, emotional distress or allergies.
Call a doctor if:
It is often difficult to decide when to see a health professional for respiratory symptoms, as you may simply have a viral infection. If you have typical cold symptoms (nasal stuffiness, mild body aches, headache, low-grade fever), treat the symptoms at home and you should soon recover from your cold.
A cold can be distinguished from classic flu in the following ways:
The diagnosis of colds is most commonly made based on symptoms and signs. Fever and more severe symptoms suggest influenza.
Most colds will be over in 7 to 10 days, and can usually be treated at home. If there is a mild fever and a feeling of lethargy in the early stages of a cold, bed rest is advisable.
The following are some practical methods that may help to alleviate cold symptoms:
There is no sure way to prevent colds, especially in children. As children grow into adults, they naturally get fewer colds.
The following may help protect you against catching colds:
Colds can't be prevented with:
Previously reviewed by Dr Eftyhia Vardas, University of the Witwatersrand
Reviewed by Prof Eugene Weinberg, Paediatrician, February 2011
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