MEDICAL MATTERS:As the days start to shorten, the flus, colds and assorted viruses start to reappear, writes Muiris Houston
YOU HAVE been feeling a bit off for 24 hours. But today you wake up with a sore throat and a dry cough. Now you are sweating and shivering with a thumping headache and muscle aches all over.
Between now and next April, many of us will experience an episode like this. Our initial reaction will be: "I have the flu." But how will we know whether it is full-blown influenza, an infection with a different virus or a bad dose of the common cold? The lack of a runny nose and sneezing and the absence of a fever suggest this is not due to the common cold.
The severity of the symptoms certainly makes influenza a possibility. If certain influenza strains are known to be circulating based on reports from the Health Protection Surveillance Centre (HPSC), then the possibility of it being the flu increases.
What objective measures do doctors use to make an influenza diagnosis? The gold standard is to send a throat swab to the National Virus Reference Laboratory which will not only tell us if influenza is present but also the subtype of the virus.
However, because of their specialist nature and the time it takes to identify the exact bug, such swabs are not routinely used in practice. Instead, doctors use clinical criteria to make a diagnosis of influenza.
These criteria include a fever of 37.8 degrees Celsius or greater and feverishness (shivers, hot and cold sweats). In addition, there must be two of the following symptoms: cough, sore throat, muscle pains and headache.
A key factor that doctors will also ask about is: "Did your symptoms come on abruptly or over a period of time?" In a classic case of influenza, patients will be off their feet within hours of the first symptoms. And a personal favourite of mine is to ask: "Can you lift your head off the pillow?" In true influenza, the patient does not want to move, such is the depth of their symptoms.
Because the initial treatment of influenza is the same as that for other viruses - bed rest, clear fluids, paracetamol and nasal decongestants - why bother trying to make an exact diagnosis?
One reason is the ability of the influenza microbe to cause significant complications, especially in older people and those with other serious health problems.
Pneumonia is the commonest complication: either a primary viral or secondary bacterial pneumonia, which can be fatal.
It is estimated that one in 50 older people require admission for heart failure brought on by the flu. Heart muscle can also be inflamed by influenza as can the brain. Young adults with influenza A infection can sometimes develop kidney failure.
All of these complications may occur during yearly outbreaks of what might be termed "regular" flu. But another reason for diagnostic vigilance is the inevitability of a major flu pandemic.
The last serious pandemic was in 1968. The 1968 virus swept around the globe. Labelled the Hong Kong flu, it was a H3N2 version of the microbe. A 1933 pandemic was caused by the H1N1 influenza virus. It disappeared for more than 40 years, before re-emerging in 1977.
It is this ability of the influenza virus to hide away for long periods that gets experts worried. And while it is a few years since we had an epidemic - defined as more than 400 cases per 100,000 people - influenza strains are continually changing from one year to the next.
The greatest flu pandemic of all - Spanish Flu - struck in 1918-1919. It was so virulent it killed up to 40 million people in less than a year, many of them healthy young adults.
Perhaps we have become a little blasé about influenza following the non-appearance (so far) of an avian (H5N1) flu pandemic. But even without this worry, there are plenty of established strains of flu out there, some from way back that could re-merge at any time.
Which is as good a way as any to remind you that this year's influenza vaccination is now in doctors' surgeries: if you are over 60 or have a chronic illness such as diabetes, asthma or heart disease, it is a must have for the winter ahead.
• Dr Houston is pleased to hear from readers at mhouston@irish-times.ie but regrets he is unable to reply to individual medical queries