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

Background: Imported fire ants (IFA) are a common cause of insect venom hypersensitivity in the southeastern United Stares. The purpose of this study was to determine the sting attack rate and development of specific 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 were surveyed for prior IFA exposure with a questionnaire, and IFA-specific IgE was evaluated with RAST and intradermal skin testing. Evaluations were performed on arrival and reported at departure from the endemic area 3 weeks later. Results: One hundred seven subjects completed the study. Field stings were reported in 55 subjects, resulting in a sting attack rate of 51%. In these 55 subjects 53 (96%) reported a pustule or a small local reaction at the sting site, one (2%) reported an isolated 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 stung subjects.