Discontinuing venom immunotherapy: Extended observations

Background: Our studies of discontinuing venom immunotherapy after at least 5 years have led to the conclusion that the residual risk of a systemic reaction to a sting was in the range of 5% to 10% in adults, and no severe or life-threatening reaction occurred with 270 challenge stings in 74 patients after 1 to 5 years without venom immunotherapy. Objective: The objective of this study was to extend our observation of patients who discontinue venom immunotherapy over 5 to 10 years and to determine which patients are at higher risk for a reaction. Methods: Patients who discontinued venom immunotherapy were surveyed for 3 consecutive years to determine the frequency of systemic reactions to field stings and the fate of venom sensitivity. The evaluation included the 74 patients previously studied (group 1) and 51 additional patients followed after stopping therapy in our clinical center (group 2). Results: Of the original 74 patients, 11 had field stings again after 3 to 7 years without venom immunotherapy, with one systemic reaction (dyspnea). Of the 51 patients in the other group, 15 were stung, of whom four (26%) had systemic reactions, including respiratory symptoms requiring epinephrine. Review of group 1 and group 2 revealed that half of the patients who had systemic reactions to a sting after stopping venom immunotherapy had a history of a systemic reaction occurring during venom immunotherapy (to an injection or a sting). Systemic reactions occurred in three patients who had negative skin test reactionS; all three had very low but detectable venom-specific serum IgE antibody levels as determined by RAST and had a history of systemic reactions during venom immunotherapy. Greater severity of the pretreatment reaction was not associated with higher frequency of reaction to stings after stopping therapy but was associated with greater severity if a reaction did occur. Conclusions: Venom immunotherapy (yellow jacket/mixed vespid) in adults can be discontinued after 5 to 6 years with a 5% to 10% residual risk of a systemic reaction. Risk factors may include history of a systemic reaction during venom immunotherapy, persistent strongly positive skin test sensitivity, and the severity of the pretreatment reaction.