MEDICAL MATTERS: Despite intensive research stretching back to the 1950s and accumulated scientific knowledge of the causes of the common cold, we are no nearer finding a cure for one of the most annoying illnesses we endure, writes Dr Muiris Houston
"I love the doctors - they are dears;
But they must spend such years and years
Investigating such a lot of illnesses which
no-one's got,
When everybody, young and old,
Is frantic with the common cold.
And I will eat my only hat
If they know anything of that!"
- A.P. Herbert 1960
For such a benign illness, the common cold is a considerable economic burden on society.
Every year in the United States, about 25 million people visit their doctor with a cold. It results in about 20 million days of absence from work and 22 million days away from school.
What is the common cold? A conventional rather than a scientific term, it describes a mild illness affecting the upper respiratory tract. Typical symptoms are stuffiness in the nose, nasal discharge, sneezing, sore throat and a cough. It tends not to cause a fever in adults, although the common cold may cause a temperature in infants.
Although the term common cold seems to imply a single cause for the illness, it is actually caused by numerous viruses that belong to several different families of microbes.
The role of different viruses in precipitating the common cold depends on factors such as the person's age, the season and the accuracy of the method used to detect the bug.
However, rhinoviruses - discovered in 1956 - are now known to be the most common cause in all age groups. During the autumn peak in the incidence of the common cold, this family of viruses causes up to 80 per cent of all upper respiratory infections.
It is likely that many colds are caused by viruses which we have yet to identify. This theory is reinforced by the recent discovery of a new virus in young children with upper respiratory symptoms. Tentatively named human metapneumovirus, early investigations suggest the virus has been circulating in humans for the last 50 years.
The common cold is a seasonal disease. In the northern hemisphere, it peaks in the autumn and remains fairly high throughout the winter before decreasing again in spring. People living in the tropics experience most colds during the rainy season.
The younger you are, the more colds you will suffer. Children get six to eight colds a year compared with two to four episodes annually for adults. Women who work outside the home have fewer infections than those working at home - this may be explained by having greater exposure to children if they stay at home. Attending a crèche or pre-school is a major risk factor for respiratory illnesses, as family doctors and parents will readily testify.
There is an unusual association between physical exercise and the likelihood of getting a cold. Moderate physical activity reduces the risk; those who engage in heavy physical training seem to be more at risk of upper respiratory infection.
Common cold viruses are transmitted in three ways: hand contact with body secretions that contain the virus - either from an infected person or from a contaminated surface; by small particles hanging in the air for a period of time; or by "direct hit" by large particle aerosols from a sneeze or cough.
The incubation period for the common cold depends on the particular virus. Rhinovirus infections tend to cause symptoms as early as 10 to 12 hours after the virus enters the nose; other viruses can be days in the system before the onset of symptoms.
A rhinovirus common cold typically starts with a sore throat followed soon after by nasal stuffiness and discharge, sneezing and coughing. Hoarseness, headache and tiredness also occur. Although muscle pain can occur, it is more typical of influenza infection.
Almost 20 per cent of children with a common cold develop an infection of the middle ear (otitis media) as a complication. Sinus infection can also complicate the common cold. Pneumonia associated with a cold is usually caused by a bacterial secondary infection separate from the causative virus.
DIAGNOSING the common cold is simple and can reliably be made by adults without reference to a family doctor. It can be less clear in younger children, where a fever may be the only early sign that something is amiss. It is understandable that despite intensive efforts, the multiplicity of viruses and strains of viruses has made finding a universal treatment impossible. The latest advances in antiviral drugs, reported recently in The Lancet, have suggested some promise for a drug called pleconaril. Preliminary findings indicate that when treatment with the drug is started within 36 hours of the onset of symptoms, the duration of the illness may be reduced by a day and a half.
As for prevention, don't hold your breath. There is no vaccine on the horizon and despite the widespread use of vitamin C and echinacea there is no conclusive evidence that they work. The only sure fire prevention is to isolate yourself completely from the community - a solution that would seem only to benefit hermits.
Dr Muiris Houston can be contacted at mhouston@irish-times.ie. He regrets he cannot reply to individual queries