Use of immune-based therapies other than IVIG such as corticosteroids (doses of prednisone greater than 0.4 mg/kg/d for more than 4 weeks within the 6 months prior to enrolling in the study or any use of corticosteroids equivalent to greater than or equal to 5 mg of prednisone at the time of enrollment) or other immunomodulating drugs within 6 months prior to enrollment in the study.