Well, if the odor is the same that's in your basement, first, you need to 'correct' that. After you correct that, maybe if you 'beat' the mattress a bit, the smell will dissipate.
If the source of the small ISN'T from your basement, then either it's time for a new mattress, a new mattress pad, or a mattress rotation. (You should have a pad and you should rotate your mattress every few months.) My best to ya and hope this helps.