Has this happened often? Also, how often do you measure the child's temperature and how do you establish the rapid uptrend?

>how often do you measure the child's temperature

As often as you need when they have a fever. Modern thermometers can give you the temperature in a minute or so.

yes, but is this sampling a good idea? Have you tried measuring temperatures periodically when the child appears well? What is the variation then? How do you know that the device is telling you something meaningful? Is the child getting flustered and hotter because of the attention?

You have to measure rectally for good results. Forhead thermometers, ear thermometers, under the tongue thermometers -- all crap. If you have an infant or small toddler, use a rectal thermometer. Measuring this way, results are both precise and accurate (and therefore, repeatable).

>yes, but is this sampling a good idea? Have you tried measuring temperatures periodically when the child appears well? What is the variation then?

There should be no major variation then. On the other hand, if the child reaches 38+ or so, you need to be on the lookout...

39C - seems about right as decision.