I'm also in the states (Texas), and my ex-step-daughter used to bring lice to our house every other weekend, because her mother would not treat at her house.
The first time she had it, she gave it to me, so treating it was TOP priority. I used NIX and the nit comb, and my step-daughter and I both had very long hair. I also washed all of the bedding in the entire house with a bleach solution (even colored items can be washed in diluted bleach if you don't over-saturate) including towels, hand-towels, sheets, comforters, stuffed animals and anything pourous. There is also a spray (I believe it is by RID?) that you can use to spray your car really well if you have cloth seats, and your couches/chairs/carpet/large items that can't be washed.
And finally, if you have a comforter or quilt or other item that absolutely cannot be washed, put it in a garbage sack and store it away (it doesn't have to be in the sunlight) for 4-6 weeks. Lice are parasites that need a host in order to live. They die in a couple of weeks without food, but you want to give them enough time for their eggs to hatch and die as well. 4-6 weeks is a good time-frame for storing the bedding away in waiting for the lice to die.
I would recommend buying 2-3 cans of the aresol spray for your house though. You'll want to spray
everything, including your carpet. Also, change out your vacuum cleaner bag and spray your vacuum thoroughly with it. If you have a mop, bleach that as well.
I got rid of the lice the first go-round! After that, every time my step-daughter would come to visit, I would make her strip all her clothes off in the laundry room and march straight back to the bathtub for a lice treatment before she could even do anything else at our house. Her clothes would go straight into the washer and her overnight bag would never enter our house - it stayed out in the garage! We had our own supply of clothes for her at our place.
Also, one tip to keep in mind. The nits or egg sacks that you see on the hair shaft take up to 2 weeks to visually see once an infestation has occured. Just because you don't
see nits in your hair, doesn't mean you don't have the lice. EVERYONE IN THE HOUSE needs to be treated with lice shampoo, whether you think they have it or not. That could be why they keep coming back.