Jennifer J. Koplin

Prevalence of challenge-proven IgE-mediated food allergy using population-based sampling and predetermined challenge criteria in infants

BACKGROUND Several indicators suggest that food allergy in infants is common and possibly increasing. Few studies have used oral food challenge to measure this phenomenon at the population level. OBJECTIVE To measure the prevalence of common IgE-mediated childhood food allergies in a population-based sample of 12-month-old infants by using predetermined food challenge criteria to measure outcomes. METHODS A sampling frame was used to select recruitment areas to attain a representative population base. Recruitment occurred at childhood immunization sessions in Melbourne, Australia. Infants underwent skin prick testing, and those with any sensitization (wheal size ≥ 1 mm) to 1 or more foods (raw egg, peanut, sesame, shellfish, or cows milk) were invited to attend an allergy research clinic. Those who registered a wheal size ≥ 1 mm to raw egg, peanut, or sesame underwent oral food challenge. RESULTS Amongst 2848 infants (73% participation rate), the prevalence of any sensitization to peanut was 8.9% (95% CI, 7.9-10.0); raw egg white, 16.5% (95% CI, 15.1-17.9); sesame, 2.5% (95% CI, 2.0-3.1); cows milk, 5.6% (95% CI, 3.2-8.0); and shellfish, 0.9% (95% CI, 0.6-1.5). The prevalence of challenge-proven peanut allergy was 3.0% (95% CI, 2.4-3.8); raw egg allergy, 8.9% (95% CI, 7.8-10.0); and sesame allergy, 0.8% (95% CI, 0.5-1.1). Oral food challenges to cows milk and shellfish were not performed. Of those with raw egg allergy, 80.3% could tolerate baked egg. CONCLUSION More than 10% of 1-year-old infants had challenge-proven IgE-mediated food allergy to one of the common allergenic foods of infancy. The high prevalence of allergic disease in Australia requires further investigation and may be related to modifiable environmental factors.

Increasing the accuracy of peanut allergy diagnosis by using Ara h 2

BACKGROUND Measurement of whole peanut-specific IgE (sIgE) is often used to confirm sensitization but does not reliably predict allergy. Ara h 2 is the dominant peanut allergen detected in 90% to 100% of patients with peanut allergy and could help improve diagnosis. OBJECTIVES We sought to determine whether Ara h 2 testing might improve the accuracy of diagnosing peanut allergy and therefore circumvent the need for an oral food challenge (OFC). METHODS Infants from the population-based HealthNuts study underwent skin prick tests to determine peanut sensitization and subsequently underwent a peanut OFC to confirm allergy status. In a stratified random sample of 200 infants (100 with peanut allergy and 100 with peanut tolerance), whole peanut sIgE and Ara h 2 sIgE levels were quantified by using fluorescence enzyme immunoassay. RESULTS By using the previously published 95% positive predictive value of 15 kU(A)/L for whole peanut sIgE, a corresponding specificity of 98% (95% CI, 93% to 100%) was found in this study cohort. At the equivalent specificity of 98%, the sensitivity of Ara h 2 sIgE is 60% (95% CI, 50% to 70%), correctly identifying 60% of subjects with true peanut allergy compared with only 26% correctly identified by using whole peanut sIgE. We report that when using a combined approach of plasma sIgE testing for whole peanut followed by Ara h 2 for the diagnosis of peanut allergy, the number of OFCs required is reduced by almost two thirds. CONCLUSION Ara h 2 plasma sIgE test levels provide higher diagnostic accuracy than whole peanut plasma sIgE levels and could be considered a new diagnostic tool to distinguish peanut allergy from peanut tolerance, which might reduce the need for an OFC.

Vitamin D insufficiency is associated with challenge-proven food allergy in infants

BACKGROUND Epidemiological evidence has shown that pediatric food allergy is more prevalent in regions further from the equator, suggesting that vitamin D insufficiency may play a role in this disease. OBJECTIVE To investigate the role of vitamin D status in infantile food allergy. METHODS A population sample of 5276 one-year-old infants underwent skin prick testing to peanut, egg, sesame, and cows milk or shrimp. All those with a detectable wheal and a random sample of participants with negative skin prick test results attended a hospital-based food challenge clinic. Blood samples were available for 577 infants (344 with challenge-proven food allergy, 74 sensitized but tolerant to food challenge, 159 negative on skin prick test and food challenge). Serum 25-hydroxyvitamin D levels were measured by using liquid chromatography tandem mass spectrometry. Associations between serum 25-hydroxyvitamin D and food allergy were examined by using multiple logistic regression, adjusting for potential risk and confounding factors. RESULTS Infants of Australian-born parents, but not of parents born overseas, with vitamin D insufficiency (≤50 nmol/L) were more likely to be peanut (adjusted odds ratio [aOR], 11.51; 95% CI, 2.01-65.79; P=.006) and/or egg (aOR, 3.79; 95% CI, 1.19-12.08; P=.025) allergic than were those with adequate vitamin D levels independent of eczema status. Among those with Australian-born parents, infants with vitamin D insufficiency were more likely to have multiple food allergies (≥2) rather than a single food allergy (aOR, 10.48; 95% CI, 1.60-68.61 vs aOR, 1.82; 95% CI, 0.38-8.77, respectively). CONCLUSIONS These results provide the first direct evidence that vitamin D sufficiency may be an important protective factor for food allergy in the first year of life.

The Natural History and Clinical Predictors Of Egg Allergy In The First 2 Years Of Life: A Prospective, Population-Based, Cohort Study

BACKGROUND There is a paucity of data examining the natural history of and risk factors for egg allergy persistence, the most common IgE-mediated food allergy in infants. OBJECTIVE We aimed to assess the natural history of egg allergy and identify clinical predictors for persistent egg allergy in a population-based cohort. METHODS The HealthNuts study is a prospective, population-based cohort study of 5276 infants who underwent skin prick tests to 4 allergens, including egg. Infants with a detectable wheal were offered hospital-based oral food challenges (OFCs) to egg, irrespective of skin prick test wheal sizes. Infants with challenge-confirmed raw egg allergy were offered baked egg OFCs at age 1 year and follow-up at age 2 years, with repeat OFCs to raw egg. RESULTS One hundred forty infants with challenge-confirmed egg allergy at age 1 year participated in the follow-up. Egg allergy resolved in 66 (47%) infants (95% CI, 37% to 56%) by 2 years of age; however, resolution was lower in children with baked egg allergy at age 1 year compared with baked egg tolerance (13% and 56%, respectively; adjusted odds ratio, 5.27; 95% CI, 1.36-20.50; P = .02). In the subgroup of infants who were tolerant to baked egg at age 1 year, frequent ingestion of baked egg (≥5 times per month) compared with infrequent ingestion (0-4 times per month) increased the likelihood of tolerance (adjusted odds ratio, 3.52; 95% CI, 1.38-8.98; P = .009). Mutation in the filaggrin gene was not associated with the resolution of either egg allergy or egg sensitization at age 2 years. CONCLUSION Phenotyping of egg allergy (baked egg tolerant vs allergic) should be considered in the management of this allergy because it has prognostic implications and eases dietary restrictions. Randomized controlled trials for egg oral immunotherapy should consider stratifying at baseline by the baked egg subphenotype to account for the differential rate of tolerance development.

Is caesarean delivery associated with sensitization to food allergens and IgE‐mediated food allergy: A systematic review

Several studies have shown differences in the composition of the gastrointestinal flora of children who develop sensitization to food allergens compared with non‐allergic children. It has been hypothesized that changes in the gut microbiota resulting from caesarean section delivery could increase a child’s risk of developing food allergy; however, studies examining the relationship between mode of delivery and food allergy have produced conflicting results. The objective of this review was to determine whether there is sufficient evidence to support an association between delivery by caesarean section and the development of sensitization to food allergens and immunoglobulin E (IgE) mediated food allergy. Using predefined inclusion and exclusion criteria, MEDLINE and PubMed were searched for studies investigating the relationship between caesarean section delivery and food allergy. The information on the quality of the studies and results were extracted and analysed systematically. The search identified four relevant studies as per our protocol. Symptomatic food allergy was used as the outcome in two studies and was found to occur more frequently in children born by caesarean section in one study while the second study found no association between food allergy diagnoses and mode of delivery. The other two studies measured levels of food antigen‐specific IgE, with both studies showing an increase in sensitization to food allergens among children born by caesarean section. Overall, there is evidence that the risk of developing IgE‐mediated sensitization to food allergens is increased among children delivered by caesarean section, however further studies using objectively diagnosed food allergy as the outcome are needed to verify whether this equates to an increase in confirmed food allergy. Future birth cohort studies should control for the effects of mode of delivery when investigating environmental modifiers of food allergy.

An update on epidemiology of anaphylaxis in children and adults

Purpose of reviewThe purpose of the present review is to describe the epidemiology of food-induced, medication-induced, drug-induced, and insect sting-induced anaphylaxis; to summarize recent changes in the incidence of anaphylaxis internationally; and to discuss recent insights into potential risk factors for anaphylaxis. Recent findingsRecent studies confirm that the incidence of anaphylaxis, particularly food-induced anaphylaxis, is increasing world-wide. The rise in anaphylaxis incidence appears most pronounced in children under the age of 5 years, which is also the age group most at risk of hospitalization for food-induced anaphylaxis. Identification of factors that may increase the risk of episodes of anaphylaxis remains an important research priority. Recently, two large cohort studies using data from electronic medical records confirmed that individuals with asthma are at higher risk of anaphylaxis and those with severe asthma have the highest risk of all. With respect to modifiable lifestyle factors, several studies have demonstrated a link between latitude and anaphylaxis, with areas with less year-round sunlight reporting a higher prevalence of food-induced anaphylaxis. SummaryReports of an increasing incidence of anaphylaxis internationally highlight the need for identification of modifiable risk factors for anaphylaxis. Emerging evidence suggests that low vitamin D levels may be associated with risk of anaphylaxis and food allergy; however, further studies are required to confirm this.

The HealthNuts population-based study of paediatric food allergy: validity, safety and acceptability

Background The incidence of hospital admissions for food allergy‐related anaphylaxis in Australia has increased, in line with world‐wide trends. However, a valid measure of food allergy prevalence and risk factor data from a population‐based study is still lacking.

Natural history of peanut allergy and predictors of resolution in the first 4 years of life: A population-based assessment.

BACKGROUND There are no prospectively collected data available on the natural history of peanut allergy in early childhood. Previous studies of predictors of tolerance development have been biased by failure to challenge high-risk children when IgE antibody levels are high, therefore potentially introducing bias to persistent allergy. OBJECTIVES We sought to describe the natural history of peanut allergy between 1 and 4 years of age and develop thresholds for skin prick test (SPT) results and specific IgE (sIgE) levels measured at age 1 and 4 years that have 95% positive predictive value (PPV) or negative predictive value for the persistence or resolution of peanut allergy. METHODS One-year-old infants with challenge-confirmed peanut allergy (n = 156) from the population-based, longitudinal HealthNuts Study (n = 5276) were followed up at 4 years of age with repeat oral food challenges, SPTs, and sIgE measurements (n = 103). Challenges were undertaken in all peanut-sensitized children at 1 and 4 years of age, irrespective of risk profile. RESULTS Peanut allergy resolved in 22% (95% CI, 14% to 31%) of children by age 4 years. Decreasing wheal size predicted tolerance, and increasing wheal size was associated with persistence. Thresholds for SPT responses and sIgE levels at age 1 year with a 95% PPV for persistent peanut allergy are an SPT-induced response of 13 mm or greater and an sIgE level of 5.0 kU/L or greater. Thresholds for SPT and sIgE results at age 4 years with a 95% PPV for persistent peanut allergy are an SPT response of 8 mm or greater and an sIgE level of 2.1 kU/L or greater. Ara h 2, tree nut, and house dust mite sensitization; coexisting food allergies; eczema; and asthma were not predictive of persistent peanut allergy. CONCLUSION These thresholds are the first to be generated from a unique data set in which all participants underwent oral food challenges at both diagnosis and follow-up, irrespective of SPT and sIgE results.

Which infants with eczema are at risk of food allergy? Results from a population‐based cohort

The relationship between early onset eczema and food allergy among infants has never been examined in a population‐based sample using the gold standard for diagnosis, oral food challenge.

Environmental and demographic risk factors for egg allergy in a population-based study of infants

Although egg allergy is the most common food allergy in infants and young children, risk factors for egg allergy remain largely unknown. This study examined the relationship between environmental and demographic factors and egg allergy in a population‐based infant cohort.