I see nits, but no lice?!
Well, in order to have nits, you had to have had an adult female lay them, as they can’t transfer by any other method. So you had a bug at one point, but sometimes, the mother lays some eggs and then travels to another head, or finds this head incompatible to her system and the mother passes after laying three eggs. Keep in mind, nits represent the next generation of lice and by doing a visual inspection there is no way of knowing that there are only nits with no live lice.
The bugs are designed by nature to be hard to see, so it is not typical to just see bugs on a head. The only way to know that there are nits with no lice present at the time is by actually treating the head! Then, during your comb-out, you would find dead bugs or discover only the eggs. You can do a thorough combing head check on wet hair and still not find any lice because they will run from you. So if we do a combing head check on someone and we find nits we know that there must have been an adult female louse there.
To answer this question properly you would have to treat somebody to find out which stages of lice are on their heads – is it just eggs or various stages of bugs, or are there are only nits with no lice. It is possible to have Nits and no lice in the very early stages of an infestation. It is also possible to have leftover nits from a prior infestation. Those would be old and unviable but with no real way to tell the difference to new lice. In that case, hiring a professional might be a good investment for your peace of mind.