One important  thing with lice is to work with their life cycle  to make sure all possible  adults have hatched out.  The poison  [or wet combing] often gets rid of the initial  infestation but unless the   last louse is removed it can start all over again.  So sometimes a child  doesn't catch them again,  they  just  still have them
The other thing is that older people can have them without  symptoms.  http://www.independent.co.uk/arts-entertainment/lice-need-understanding-1196548.html
  Apparently in our area according to the school nurse   they are often caught from grandparents,  so  it's worth making sure you check the whole family

info on  a  wet coming regime can  be found here,  which takes into account the  need for repeat combings. www.chc.org 
With anything to do with any insects understanding  the lifecycle is crucial whether you're trying to  eradicate them or manage them

I've only had them once,  caught from  my daughter when she was about 10.  Personally  would  not use the  poisons  and   neither of us have had them again. 

Helen
England



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