I feel your pain ladies, when we lived in Darwin DD1 had waist length hair and had nits heaps which drove me insane!!
We have 2 families at our school now who have recurrent nit problems and it got to the stage where as soon as we saw the nits in their hair we'd call mum to come and get them because it wasn't fair on the other families whose kids were constantly getting reinfected.
Sadly it takes just one parent who doesn't bother treating properly to spread it and keep it going.