NATURAL-HISTORY OF HYMENOPTERA VENOM SENSITIVITY IN ADULTS

Background: Epidemiologic studies of Hymenoptera venom allergy in adul ts show a prevalence of positive venom skin test results. RASTs of 15% to 25%, or both, but most such individuals have had no systemic react ions to stings. The clinical significance and natural history of this apparently common sensitivity is uncertain. Objective: We sought to de termine the natural history of venom sensitization by observing the ra te of decrease or increase in sensitivity in normal adults over 5 to 1 0 years. The clinical significance of these findings is related to the frequency of systemic reactions to stings during the period of observ ation.Methods: Serial observations were planned in 520 volunteers and randomly selected subjects. Two follow-up visits were attempted, once after 2 to 3 years and again after 5 to 9 years, to perform repeat ven om skin tests and RASTs and to review any history of interim stings an d their outcomes. Results: Follow-up visits were conducted with 398 su bjects (375 early visits and 205 late visits). Overall, in the 398 sub jects with one or more visits after a mean of 4 years, skin test respo nses changed from positive to negative in 44 of 98 (45%) and from nega tive to positive in 27 of 309 (8.7%) of the subjects. Skin test respon ses changed from positive to negative in 29 of 87 (33%) subjects after 2.5 years and in 43 of 54 (80%) after 6.8 years. Even when the skin t est response became negative, venom-specific IgE remained positive in 11 of 29 (38%) subjects after 2.5 years and in 13 of 43 (30%) after 6. 8 years. The rate of loss of sensitivity was 12% per year, similar to retrospective estimates. Skin test sensitivity to venoms disappears mo re rapidly in these subjects without symptoms (half-life, 4 years) tha n in patients receiving venom immunotherapy (half-life, 7 years). Skin test responses changed from negative to positive in 23 of 288 (8%) su bjects after 2.5 years and in 9 of 151 (6%) after 6.8 years. Insect st ings caused no reaction in 120 subjects with a negative skin test resp onse, but 17% (11 of 65) of subjects with a positive skin test respons e (but with a negative history had systemic reactions when stung. Ther e was no difference between the early and late visits in the frequency of systemic reactions reported. The risk may be higher than 17% for t he specific individuals (67% after 2.5 years and 20% after 6.8 years) whose positive skin test responses persist for years. This risk is low er than that of patients with a positive history (50%) but higher than that of ''normal'' adults or venom-treated patients (<2%). It is stil l not clear whether any subset of adults with a positive skin test res ponse but a negative history can be identified, in whom the risk of sy stemic sting reaction would justify venom immunotherapy even before an y reaction occurs. Conclusion: Asymptomatic venom sensitization in adu lts is common but transient, disappearing at the rate of 12% per year. However, the risk of a systemic reaction to a subsequent sting is sig nificant in adults without symptoms but with positive venom skin test responses (17%) and may be higher when skin test sensitivity does pers ist for years.