Clinical and entomological factors influence the outcome of sting challenge studies

Background: The reported frequency of systemic reactions to challenge sting varies greatly. Objective: To evaluate the interaction of clinical and entomological factors that determine the outcome of a challenge sting. Methods: Patients allergic to yellow jacket were stung and monitored for systemic reaction. The frequency and severity of sting reactions were analyzed in relation to the species of insect used and patient characteristics. Results: Objective systemic reactions occurred in 21 of 69 patients (30%) stung with Vespula maculifrons and in 8 of 71 patients (11%) with Vespula germanica (P = .005). Systemic reactions were more frequent in patients with a severe history (9/30; 30%) than in those with a mild or moderate history (21/145; 14%; P = .04). In only 1 of 111 patients (0.9%) was the reaction to sting challenge more severe than previous reactions. The reaction rate was higher when venom skin tests were positive at <1.0 mu g/ml, (17/75 = 23%) than when sensitivity was milder (9/100 = 9%; P = .012). We compared sting outcome and venom-induced histamine release in relation to insects collected in July or in October, and found no difference. Conclusion: Allergic reactions to sting challenge are determined by the species of yellow jacket used, the severity of previous sting reactions, and the degree of skin test sensitivity, but not by the time of year. These factors are important to clinicians when they evaluate the chance of reaction to a future sting and to researchers when they design and report sting challenge studies.