Here we are at a change of season period of the year. Whether in the northern or southern hemisphere this period of change tends to be associated with increases in the incidences of particular conditions.
In the north, in early autumn, there tends to be an increase in the incidence of early viral infections. The colds are available for the truely early adopters, those who get an early bout now and either get through the winter without a second cold or are one of those whose immune system is now begining this year’s series of infections.
In the south it is the beginning of spring and as pollen counts climb so does the incidence of allergies, especially hay fever. Again, for some spring is the only time of year they feel bothered by allergies while for those with a weakened immune system it merely adds further to their symptom patterns.
Interestingly, many people who have hay fever mistakenly think they have a viral infection, such as a common cold. Even worse, they sometimes think they have an infection requiring antibiotics.
I say worse, because even though they probably don’t have any bacterial infection, and therefore do not require antibiotics, at least some of them will persuade their doctor to prescribe them. There are many reasons why it is very bad to take unnecessary antibiotics but I will leave that for another day.
If someone feels unwell, is lethargic, has a sore throat, stuffy head, possible headache and/or earache, mild to moderate cough, maybe runny nose and watery eyes along with some sneezing, they often think they have a cold or some other viral illness. Other people they know may have similar symptoms so they assume they have "caught it".
They may well be perfectly correct. But they may have hay fever or some other allergy. Of course there is no law that says they can’t have both, though the tendency is not to. So it is likely to be one (the provisional diagnosis) but may be the other (the differential diagnosis), or something else entirely, since many diseases present like this in the early stages.
On examining someone with these presenting symptoms and signs further details will be gathered. For example, the throat will be examined, as will the eardrums, the lymph node will be checked and the temperature taken. A history will also be gained. Knowing how it started, how quickly it developed and so forth will give further clues to support a diagnosis.
This is because epidemiologists (people who study and document the patterns of features and spread of disease and determinants of health in society at large) have taught us how to match the details obtained with what is known about certain conditions. This isn’t foolproof, but it is a huge help. It also helps if you are the umpteenth person to present with the same pattern in the last couple of days and it is pretty clear that a virus is in the area!
With all this data a reasoned judgement is made and appropriate treatment may be chosen. Mostly, in simple cases such as this the diagnosis is correct (even if the treatment leaves plenty to be desired). Sometimes of course, the diagnosis is incorrect. So what else could be done to make a correct diagnosis?
One thing could be a swab of a suspicious area, such as a very sore throat. This swab would be sent for culture of any bacteria present and determination of their antibiotic sensitivity to ensure an appropriate prescription. This is slow and expensive and tends to be reserved for people facing other health risks.
The other thing obviously is a blood test. This can be much quicker but is still expensive and more invasive in that a needle puncture is used to collect the sample. However, if there are reasons why it is very important to know what the cause really is, this is quite a good way to find out.
The blood test will involve a white cell count, including a differential breakdown of the individual white cell types. You may have seen this written up as a "WCC and Diff". This becomes very revealing because different conditions cause different, but particular, responses.
A raised total white cell count simply indicates that the immune system is marshalling resources to attempt to remove something. If that was the only result we had it would not advance our decision-making much at all. However, knowing which white cells are elevated tells us much more.
For example, an abnormally high count of eosinophils (ie eosinophilia) is associated with an allergic response and the correct diagnosis would probably be hay fever. Different patterns will indicate viral infections and bacterial infections.
So when you really need to know, for example in electing to avoid an antibiotic, the white cells tell all.
