Background: Anaphylactic sting reactions in patients with Hymenoptera venom allergy are prevented by venom immunotherapy (VIT) in most patients.

Objective: The aim of this study was to investigate re-sting reactions in the field during VIT or during an observation period of up to 13 years after cessation of treatment. Furthermore we sought to identify patients at higher risk of developing a systemic allergic reaction (SAR) and to assess possible correlations with basal serum tryptase
concentration.

Methods: The clinical data of 192 patients with a recorded field sting during VIT were evaluated and the patients were questioned regarding possible re-stings after cessation of VIT. Baseline mast-cell tryptase concentrations and specific IgE were analyzed in patients with a reported SAR.

Results: Of 192 patients with reported re-stings in the field, 27 developed SARs (14.1%). A SAR occurred in 11.9% of the stings delivered during VIT, whereas 9.7% of the stings resulted in a SAR after VIT. The majority of SARs in response to a field sting during VIT were mild, whereas severe SARs occurred more often after VIT and repeated reexposure. Out of 23 patients with reported SARs, 2 (8.7%) had elevated basal serum tryptase.

Conclusions: VIT lasting for at least 3 years is effective in protecting the vast majority of patients. The individual predictability of the response of patients to a field sting is low. SARs of increased severity mainly occur after therapy and after tolerating consecutive stings.

Key words: Field sting. Hymenoptera venom allergy. Mast cell tryptase. Systemic allergic reaction. Venom immunotherapy.