my daughter is 15 years old... for the last 8 years she has been afflicted with pinworms... she has had them throughout the year... even in december.. we probably treat her 3-4 times a year... with vermox.. the pinworms continue to return. she does not play in dirt. she also has dysmenorrhea and constant sinus issues. could the pinworms develop an immunity to vermox and are not being eradicated? if that is true, with this cause other illnesses to occur? her current doctor is confused has to why she continues to have pinworms. we treated her a month ago, with 2 doses of vermox, and a dose of pin-x.. last night she had pinworms return. can she get these from swimming in ponds? but still do not understand how she develops them in the winter months... any suggestions