Lice is everywhere. There is nothing that can prevent it other than total seclusion from all society. When you are at Walmart at any given time our health department nurse said that over half the people have at least one live bug in their hair.
They are everywhere.
Go to headlice.org.
They have the facts, not old wives tales that are rumor and don't do anything but waste time and money. Many of the items a person is told to buy to fight this issue is useless, they do nothing. Read facts, not boxes of stuff that will make the company a bit of money.
I wash our girls waist length hair in regular shampoo, condition it, comb it with a wide tooth comb to de-tangle, then have her sit in a little tykes chair with her head under the lamp light. I use a head gear style magnifying glasses from Hobby Lobby.
The water stuns the bugs so they don't move very fast. I section off her hair and start going through it in about 1" areas. I move quickly. I check her hair about 1-2 times per week if she has had any live bugs. I have beside me a glass of water and a rat tail comb, a natural bristle brush, some tweezers, and maybe some tiny scissors. If there is a section with several nits in it I will clip the individual hairs they are on but normally I just use my fingertips and slide the nit down the hair shaft and drop it in the water.
She has not had chemicals used on her hair. It usually takes 1-2 times of me going through her hair after seeing a nit for her hair to be nit and bug free.
There is a cream you can get the doc to prescribe. They put it on dry hair and then leave it on for the day or over night. It is called Lindane. It is like the shampoo but is much milder since you have total control of how much you apply. I have a friend who has a daughter that lives in a small town that fights head lice every year throughout the whole school. This girl will come to visit her mom for the weekend and they will get head lice each time. The only way she was able to stop the lice in their tracks was to apply this cream to her kids hair on Saturday morning and leave it on all day. They washed it off that evening. After doing this to her daughter that does not live with her she didn't get lice after a while anymore. The cream is not to be used more that once or twice though.