Background: In Mediterranean regions, double sensitization to Polistes and Vespula species is frequent in patients reacting to an unidentified wasp sting. Since both genera are present, it is often difficult to determine which insect is responsible and, consequently, select venom for immunotherapy. When a specific diagnosis cannot be made, a new therapeutic strategy should be undertaken.

Methods: We performed a case-control study in which 37 patients who were allergic to venom from Vespula and Polistes species received a 3-year schedule of alternating immunotherapy. Twenty monosensitized patients (10 to Vespula and 10 to Polistes) received conventional venom immunotherapy (VIT) during the same period. All 57 patients received the same number of injections. The effectiveness of VIT was assessed by means of re-sting, which was performed yearly. Serum specific immunoglobulin (Ig) E and IgG4 were also studied.

Results: All the cases tolerated all the stings. One control patient developed a mild systemic reaction after the first-year Vespula sting but tolerated subsequent re-stings. Both cases and controls reached significant changes in levels of IgE and IgG4 after VIT (P<.04 at minimum). The cases developed a response as expected, although this was less intense than in the control group. In the Polistes control subgroup, sIgE to Polistes decreased to under baseline levels, after a marked initial increase; this decrease was not observed in the Vespula subgroup.

Conclusion: An alternating VIT strategy is appropriate and provides protection to patients sensitized to Vespula and Polistes.

Key words: Venom Immunotherapy. Polistes. Vespula. Hymenoptera allergy.