Head lice are spread very easily from one person to another. If a person in a household gets infested, it is really likely that all members of the household will also become infested. In addition, close friends, and extended family members may also catch lice, depending on how much contact there is with the infested person. For this reason, re-infestation can be a real issue, and occurs frequently, but there are some precautionary actions you can take to help avoid this.

If you should discover that someone in your family has head lice, it is imperative that the person be treated for the infestation as soon as possible. The longer you wait, the more miserable the person will get, and the more chance that the head lice will spread to others.

If one person in the family has head lice, check all members of the household for signs of infestation, and treat all people who appear to have nits or lice.
Inform those who have had contact with the infested person that they should examine their head for signs of head lice. It may also be a good idea to inform the school nurse so that a note can be sent home for members of the class to check for lice.

After treatment, completely clean the house, vacuuming all surfaces that can be vacuumed, including furniture. You will also want to wash all linens, towels, coats, scarves, etc. Whatever can't be laundered, should be placed in a plastic bag, and sealed for at least two weeks; this includes stuffed animals, pillows, and all items needing dry cleaning.

For the next few weeks it will be necessary to examine everyone's hair for signs of re-infestation. If you missed some nits, or the treatment did not kill all the head lice, you will quickly see signs of a returning infestation.
Even if you do not see any evidence of nits or lice, it may be a good idea to use a metal nit removal comb to run through the hair every night. This will help to ensure that you catch any nits that you may have missed during the initial combing.

In the case that there is a re-infestation of head lice, it is important to remember that all the above steps must again be taken. This procedure will continue until the head remains clear for at least one month after treatment.