My DD goes to a private school and they get an occasional outbreak of nits. DD has had them once (so far). And gave them to me - the first time I'd ever had them (and I went to state schools)
So, nits are egalitarian. To be fair, the school does seem to be efficient at dealing with the problem - notes go out telling everyone to do a combing, and children who have them aren't supposed to come back to school till they are treated. I seem to remember on a previous nit thread that state schools tended not to deal with the problem effectively.