Imported fire ant allergy in young children: skin reactivity and serum IgE antibodies to venom and whole body extract.

We studied 19 young children (aged 15 to 39 months) who had had a systemic allergic reaction after imported fire ant (IFA) sting. Skin testing was performed with whole body extract (WBE) of both Solenopsis species; positive reactions to S. invicta was noted in 94% and to S. richteri in 100%. Serum was tested for total IgE level and for specific IgE antibodies by RAST with WBE and venom (V) of S. invicta. In vitro results were compared with those of 19 age and sex-matched atopic control subjects. The range of total serum IgE level was 31 to 1720 IU/ml (geometric mean 160 IU/ml), compared with 7.5 to 6756 IU/ml (geometric mean 85 IU/ml) in the control subjects. The difference between the two groups, however, was not statistically significant (p greater than 0.05). In the IFA-allergic group, the IFA WBE RAST mean binding was 13.5% (range 2.0% to 30.2%), and the IFA V RAST mean was 29.2% (range 7.8% to 46.7%). The control sera demonstrated low levels of activity to both IFA WBE RAST (0.7% to 4.8%) and IFA V RAST (0.7% to 5.9%). IFA WBE RAST demonstrated that 26% of the IFA-allergic patients had counts within the range of the atopic control subjects. In contrast, the IFA V RAST clearly separated all IFA-allergic patients from their age and sex-matched atopic control subjects. A scoring system for IFA V RAST is proposed. These results demonstrate superiority of IFA V over IFA WBE RAST in the diagnosis of allergy to S. invicta.