Methods: From a previously described cohort of 56 prawn allergic patients (Thayalasingam, Clin Exp Allergy 2014), 17 patients agreed to be recruited. Six monthly questionnaires were administered and skin prick tests (SPT) to house dust mites (HDM): Dermatophagoides pteronyssinus (Dp), Dermatophagoides farina (Df), Blomia tropicalis (Bt), crude extracts to crab, prawn and custom made extracts of 3 prawn species (Penaeus monodon [tiger prawn], Litopenaeus vannamei [glass prawn], and Panadalus borealis[angka prawn]). Sera for IgE sensitization measured via ImmunoCAP to Dp, Df , Bt and Shrimp were also collected and compared to previous data from the same patients.
Results: Of the 17 patients, 2 had a history of anaphylaxis, 8 had a positive oral food challenge (OFC), 7 had a negative OFC at recruitment. Their mean age was 39 years (range:8 - 61 years) at recruitment. The duration of follow-up ranged from 34 to 76 months (mean 48 months). Sixteen (94%) (anaphylactic=2, OFC(+)=8, OFC(-)=6) continued to eat prawn and 14 (87.5%) still had ongoing allergic reactions. Two patients tolerated regular consumption of prawn, 1 of whom had a previous positive OFC.
Comparison of the clinical symptoms showed that the most common symptoms were urticaria (80%), throat itchiness (53.35%), generalized redness of skin (40%), nasal congestion (33.3%) and lip swelling (33.3%). There was a significant decrease in number of hospital visits for allergic reactions (at recruitment=29.4% to follow-up=0%, p<0.05).
The frequency of positive SPT to prawn extracts decreased from 11/17 subjects at recruitment compared to 7/17 subjects on follow up, but this was not statistically significant. There was no change in specific IgE levels to shrimp and dust mites except for a significant decrease in sIgE Df (p<0.05).
Conclusion: Prawn allergy is relatively longstanding. OFC negative subjects may continue to have allergic reactions on exposure, suggesting loss of tolerance or intermittent presence of co-factors lowering threshold for allergic reactions