THE NATURAL-HISTORY OF EXPOSURE TO THE IMPORTED FIRE ANT (SOLENOPSIS-INVICTA)

Background: Imported fire ants (IFA) are a common cause of insect veno m hypersensitivity in the southeastern United Stares. The purpose of t his study was to determine the sting attack rate and development of sp ecific IgE in an unsensitized population. Methods: Study participants consisted of 137 medical students with limited exposure to IFA-endemic areas who were temporarily training in San Antonio, Tex. Subjects wer e surveyed for prior IFA exposure with a questionnaire, and IFA-specif ic IgE was evaluated with RAST and intradermal skin testing. Evaluatio ns were performed on arrival and reported at departure from the endemi c area 3 weeks later. Results: One hundred seven subjects completed th e study. Field stings were reported in 55 subjects, resulting in a sti ng attack rate of 51%. In these 55 subjects 53 (96%) reported a pustul e or a small local reaction at the sting site, one (2%) reported an is olated large local reaction, and none reported a systemic reaction. At the 3-week follow-up skin test and RAST conversions occurred in seven subjects (13%) and in one subject (1.8%), respectively. Conclusions: Even brief exposures to IFA-endemic areas result in significant sting rates and concurrent rapid development of IFA-specific IgE in 16% of s tung subjects.