Before waging on through sickness, I always take into account its severity and duration.
Also, how does your body normally handle illness?
Do you normally recover fast, or are you the type that gets the sniffles one morning and is sick for the next 5 weeks?
If you feel well enough to train go ahead.
But if you feel like you’re getting worse, or if the thing just doesn’t want to go away, lay off, rest, and let your immune system do its job.