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.

Diagnostic tests for food allergy.

The diagnosis of food allergy is still based primarily on a detailed medical history and comprehensive physical examination. Clinical or laboratory tests only serve as an add-on tool to confirm the diagnosis. The standard techniques include skin prick testing and in-vitro testing for specific IgE-antibodies, and oral food challenges. Properly done, oral food challenges continue to be the gold standard in the diagnostic workup. Recently, unconventional diagnostic methods are increasingly used. These include food specific IgG, antigen leucocyte antibody and sublingual/intradermal provocation tests, as well as cytotoxic food and applied kinesiology and electrodermal testings. These lack scientific rationale, standardisation and reproducibility. There have been no well-designed studies to support these tests, and in fact, several authors have disproved their utility. These tests, therefore, should not be advocated in the evaluation of patients with suspected food allergy because the results do not correlate with clinical allergy and may lead to misleading advice and treatment.

Prevalence of drug allergy in Singaporean children.

INTRODUCTION: Adverse drug reactions (ADRs) are a common medical problem in children, affecting up to 15 percent of children, according to the literature. However, most studies on ADRs were performed in a hospital setting, and studies in the general population are limited. The current study aims to estimate the prevalence of ADRs in a large number of non-selected Singaporean children. METHODS: School children, aged 7-16 years, from 25 random schools were screened via a self-reported questionnaire on ADRs, and parents of the selected children were then followed up with a telephone interview to obtain additional information on specific manifestations, diagnosis and allergy testing. RESULTS: The prevalence of an ADR in children was 5.4 percent, with 56.7 percent of cases reporting an ADR to beta-lactam antibiotics. Dermal manifestations were reported in 60 percent of all ADRs, while multiple drug allergies accounted only for 3.8 percent. Only 6.9 percent of the children who experienced an ADR were referred to a hospital for further investigations. CONCLUSIONS: ADRs were associated with a positive history of atopy, increased income level and Chinese and Indian ethnicity, but not with gender or age. It is striking that most children suffering from a clinical ADR were not investigated further or referred for diagnostic tests. Many parents were unaware of the availability of drug allergy tests and feared compromising their children's health. This certainly could attribute to the high incidence of the over-reporting of ADRs in the general population.