Skin Prick Testing
Tree nut SPT will include both fresh tree nuts and commercial extracts almond, cashew pecan (Greer), brazil nut, pistachio, walnut (ALK USA) and hazelnut and macadamia (Immunotek)]. Peanut SPT will be via commercial extract only (Greer). Any participant reacting to the multi-nut OFC or on home introduction of an individual tree nut will undergo SPT to tree nuts. At 18 months of age follow up peanut and tree nut SPT will be performed regardless of ingestion or allergy history to capture sensitized tolerant participants.
Allergens will be applied to the child’s back and standard single lancet technique will be used with a Quintip device. Wheal size will be calculated as the average of the length and width of the wheal after 15 minutes. A positive SPT will be defined as a wheal diameter at least 3 mm greater than that produced by the negative control solution at 15 minutes. For allergens tested with extract and fresh nuts, a mean wheal diameter ≥3 mm for either method will be considered positive.
Individual Nut Oral Food Challenge s
Participants sensitized to peanut or any tree nut will undergo individual nut OFC using a modified version of the Australasian Society of Clinical Immunology and Allergy (ASCIA) Peanut or Tree Nut Challenge Protocols [22]. The top dose has been reduced from 2 teaspoons to one teaspoon for the TreEAT trial due to the younger age of participants. The individual peanut or tree nut OFC will consist of 6 increasing doses at 20minute intervals (Smear, 1/16tsp, 1/8tsp, ¼ tsp, 1/2tsp and 1 tsp).
A positive multi nut or individual nut food challenge will be defined based on modified PRACTALL criteria [23] and in summary will consist of any one of the following: ≥3 concurrent non-contact urticarial wheals, facial angioedema, vomiting and /or anaphylaxis (respiratory or cardiovascular symptoms) within 1 hour of the last dose.