Clinical and immunochemical profiles of food challenge proven or anaphylactic shrimp allergy in tropical Singapore.

BACKGROUND: Shellfish allergy in Singapore is highly prevalent, and shrimp allergy is the most common. OBJECTIVE: This study aims to evaluate the clinical characteristics and immunological phenotype of shellfish allergy in this population. METHODS: Patients with self-reported shellfish allergy were recruited from outpatient clinics of three large hospitals and from a population survey. Open oral food challenges (OFC) to glass prawn (Litopenaeus vannamei) and tiger prawn (Penaeus monodon) were carried out on all patients except for those who had a history of severe anaphylaxis. Skin prick tests (SPT) and specific IgE to crude and recombinant allergens were carried out to evaluate shrimp and dust mite sensitization. Immunoblots were used to assess IgE-binding proteins. RESULTS: The 104 patients recruited were categorized into shellfish allergic (SA) when OFC was positive or had a history of severe anaphylaxis (n = 39), shellfish tolerant (ST) when OFC was negative (n = 27), and house dust mite positive controls (HDM(+) ) who were ST (n = 38). Oral symptoms (87.1%) were the predominant clinical manifestation. Positive challenge doses ranged from 2 to 80 g of cooked shrimp, with 25/52 patients reacting to either one or both shrimps challenged. The presence of specific IgE to shrimp either by SPT and/or ImmunoCAP(®) assay provided diagnostic test sensitivity of 82% and specificity of 22.2%. The inclusion of specific IgE to shrimp tropomyosin and IgE immunoblots with shrimp extracts did not improve the diagnostic proficiency substantially. CONCLUSIONS AND CLINICAL RELEVANCE: This study highlights the predominance of oral symptoms in shrimp allergy in tropical Asia and that a high provocation dose may be necessary to reveal shrimp allergy. Furthermore, specific IgE diagnostic tests and immunoblots were of limited use in this population.

Anaphylaxis to galacto-oligosaccharides--an evaluation in an atopic population in Singapore.

Anaphylaxis to galacto-oligosaccharides (GOS), a prebiotic, has been described in atopic patients following its supplementation in commercial milk formula in South-East Asia. The epidemiology of this usual allergy to a carbohydrate is unknown. This study evaluated the prevalence of allergy to two formulations of commercial GOS, Vivinal™ GOS (vGOS) and Oligomate™ , in an atopic cohort. Atopic subjects (n = 487) from two specialist allergy clinics were surveyed via structured questionnaire and underwent skin prick tests to GOS. Subjects with positive skin prick tests to GOS (n = 30, 6.2%) underwent basophil activation tests, and a subset (n = 13) underwent oral challenge tests to both formulations of GOS. Six subjects had positive challenges to vGOS; and none to Oligomate. By extrapolating the BAT and oral challenge results, the prevalence of allergy to vGOS is estimated at up to 3.5% (95% CI 2.2-5.5%) of our atopic population. Our findings show that GOS allergy may be common amongst atopics in Singapore.