This is from the Royal Childrens Hospital website
Unfortunately, repeat infection is very common. To help reduce this and to prevent the threadworms from spreading to others, you can take the following precautions:

  • Treat all other family members at the same time. Adults can also get threadworms.
  • It is not necessary to "worm" the family when you worm the family pets-dogs and cats do not get threadworms or pass them on the people.
  • Encourage your child not to scratch, despite the itching.
  • Keep your child’s fingernails clean and trimmed. Stop children from nailbiting or thumb sucking.
  • Have your child wash his/her hands with warm soapy water for at least 10 seconds after going to the toilet.
  • Launder bedding and toys in hot water.
  • Vacuum often, to remove any eggs.
  • Discourage your child from eating food that has fallen on the floor.