Diagnosing illness

Halifax paediatrician Brett Taylor says figuring out what ails is you can be an art. Imagine, he says, that you are an emergency paediatrician, seeing a six-year old child with a fever and a sore, red throat. What do you do?

Most of these children have viral illnesses, but about five per cent have strep throat; you might consider doing a throat swab to find out. Unfortunately, about 10 per cent of all children, including those with a viral infection, carry strep as a "colonizing bacteria". That is, the strep is causing no illness — but a throat swab will say the child has strep.

The combination of fever, sore throat and a positive throat swab means the odds are two to one against the child having strep throat. Now, experienced emergency docs don't swab every kid with a red throat.

They use their clinical skills to weed out those likely to be viral, and swab the rest. There are limits to how well they can do this

When you go to the doctor, are you looking for a confirmation of a diagnosis you have already made?