The Natural History of Egg Allergy in an Observational Cohort
Scott H. Sicherer, MD
1,*
, Robert A. Wood, MD
2,*
, Brian P. Vickery, MD
3
, Stacie M. Jones,
MD
4
, Andrew H. Liu, MD
5
, David M. Fleischer, MD
5
, Peter Dawson, PhD
6
, Lloyd Mayer,
MD
1,**
, A. Wesley Burks, MD
3
, Alexander Grishin, PhD
1
, Donald Stablein, PhD
6
, and Hugh
A. Sampson, MD
1
1
Department of Pediatrics, Icahn School of Medicine at Mount Sinai, New York, NY
2
Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, MD
3
Department of Pediatrics, University of North Carolina, Chapel Hill, NC
4
Department of Pediatrics, University of Arkansas for Medical Sciences and Arkansas Children’s
Hospital, Little Rock, AR
5
Department of Pediatrics, National Jewish Health, Denver, CO
6
The EMMES Corporation, Rockville, MD
Abstract
Background—There are few studies on the natural history of egg allergy and most are single
site, not longitudinal, and have not identified early predictors of outcomes.
Objective—To describe the natural course of egg allergy and to identify early prognostic
markers.
Methods—Children aged 3–15 months were enrolled in a multicenter observational study with
either a convincing history of an immediate allergic reaction to egg and/or milk with a positive
prick skin test (SPT) to the trigger food; and/or moderate-severe atopic dermatitis and a positive
SPT to egg or milk. Children enrolled with a clinical history of egg allergy were followed
longitudinally and resolution was established by successful ingestion.
Results—The egg-allergic cohort consists of 213 children followed to a median age of 74
months. Egg allergy resolved in 105 (49.3%), at a median age of 72 months. Factors that were
most predictive of resolution included the following: initial reaction characteristics (isolated
urticaria/angioedema vs other presentations), baseline egg-specific IgE level, egg SPT wheal size,
atopic dermatitis severity, IgG4 and IL-4 response (all P<0.05). Numerous additional baseline
clinical and demographic factors and laboratory assessments were not associated with resolution.
Multivariate analysis identified baseline egg-specific IgE and initial reaction characteristics as
strongly associated with resolution; a calculator to estimate resolution probabilities using these
variables was established.
© 2013 American Academy of Allergy, Asthma and Immunology. Published by Mosby, Inc. All rights reserved.
Corresponding Author (and reprint requests): Scott H. Sicherer, MD, Division of Allergy/Immunology, Mount Sinai Hospital, Box
1198, One Gustave L. Levy Place, New York, New York 10029-6574. Voice: (212) 241-5548; FAX: (212) 426-1902;
scott.sicherer@mssm.edu.
*
Drs. Sicherer and Wood contributed equally to this manuscript
**
Deceased.
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NIH Public Access
Author Manuscript
J Allergy Clin Immunol. Author manuscript; available in PMC 2015 February 01.
Published in final edited form as:
J Allergy Clin Immunol. 2014 February ; 133(2): 492–499.e8. doi:10.1016/j.jaci.2013.12.1041.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
Conclusions—In this cohort of infants with egg allergy, about one half had resolved over 74
months of follow-up. Baseline egg-specific IgE and initial reaction characteristics were important
predictors of the likelihood of resolution.
Keywords
egg allergy; natural history; food allergy; IgE
INTRODUCTION
Allergy to egg is estimated to affect 0.5–2.5% of young children,
(1–4)
with a recent estimate
of up to 8.9% of infants reacting to raw egg in one study from Australia.
(5)
Having an egg
allergy, or being sensitized to egg, is associated with increased risks of peanut and other
food allergies, atopic dermatitis (AD) and development of respiratory allergies and
asthma.
(6–9)
For those with egg allergy, avoidance is difficult and allergic reactions from
accidental ingestion are common.
(10)
Fortunately, egg allergy typically resolves during
childhood.
(11–14)
However, the rate of resolution may be slowing, with a past study
suggesting the majority are egg tolerant by age 3 yrs
(13)
and a recent study suggesting about
half of children reach tolerance by age 12 yrs.
(11)
The recent study from a referral
population showed persistent egg allergy for 42% of children in late adolescence,
(11)
suggesting the number of egg allergic adults may increase with time, although the current
estimate of egg allergy among adults is 0.2%.
(9)
The ability to determine prognosis of egg
allergy is critical because potential interventions under study carry risks
(15)
and ideally
would be applied in those unlikely to achieve resolution naturally.
The Consortium of Food Allergy Research (CoFAR) enrolled 512 infants with likely egg or
milk allergy, but without previously known peanut allergy, in a multicenter observational
study to address the immunologic, genetic, and environmental factors that affect the natural
course of food allergy.
(16;17)
Evaluations were offered every 6 months and oral food
challenges (OFC) were offered as clinically indicated, similar to the studies described
above.
(11–14)
We previously reported the natural course of milk allergy in this cohort and
identified a number of prognostic markers that could be used to estimate resolution rates
utilizing baseline characteristics.
(18)
The primary aim of the current analysis is to assess the
natural history of egg allergy in the infants enrolled in this cohort, with a focus on the
clinical factors predicting the resolution of egg allergy over the first six years of life.
METHODS
Subjects, study definitions and procedures
The subjects of this study are an egg-allergic subset of a larger cohort of 512 infants
originally enrolled at 3–15 months of age at 5 sites (egg allergic children/total enrolled per
site): The Icahn School of Medicine at Mount Sinai, New York (47/106); Duke University
Medical Center, Durham, NC (now followed at the University of North Carolina, 20/103);
Johns Hopkins University School of Medicine, Baltimore, MD (37/109); National Jewish
Health, Denver, CO (42/99), and Arkansas Children’s Hospital, Little Rock, AR (67/95) as
described previously.
(16;18)
Enrollment criteria for the whole cohort were designed to
include atopic children with likely egg or milk allergy at risk to develop peanut allergy, but
without current peanut allergy. Briefly, enrollment required either (1) a history of a
convincing immediate allergic reaction to egg and/or cow’s milk and a positive skin prick
test (SPT) to the trigger food, and/or (2) moderate to severe AD, and a positive SPT to egg
and/or milk. Exclusion criteria included clinical evidence of peanut allergy or peanut-
specific IgE > 5 kU
A
/L identified prior to enrollment.
(16;18)
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The subgroup of children in the current study had a diagnosis of egg allergy at the time of
enrollment, or acquired this diagnosis after enrollment with no prior evidence of egg
tolerance. Study procedures were reviewed and approved by the National Institutes of
Allergy and Infectious Diseases Data Safety Monitoring Board and by local site Institutional
Review Boards, and written signed consents were obtained.
Participants were considered egg-allergic if their initial reaction was either (1) a positive
physician-supervised OFC; (2) a convincing reaction (defined by symptoms within an hour
of isolated ingestion that included at least urticaria and/or angioedema, difficulty breathing,
wheezing, throat tightness, and/or vomiting) AND sensitization to egg (egg-specific IgE
≥0.35 kU
A
/L and/or SPT ≥ 3 mm); or (3) a flare of AD associated with egg ingestion AND
an egg-specific IgE level greater than 2 kU
A
/L, a level which is >95% predictive of egg
allergy in infants.
(13)
Reaction details were recorded regarding skin, oral, respiratory,
gastrointestinal and cardiovascular symptoms. The study analyzed 3 mutually exclusive
initial clinical presentations of reaction to egg ingestion: AD diagnosis (flare of AD), skin
only (acute hives and/or angioedema) or systemic (e.g., more than isolated skin, including
respiratory and gastrointestinal reactions). Subjects were considered egg tolerant if they
ingested whole, concentrated egg products (scrambled egg, French toast) in serving size
quantities without symptoms either during physician-supervised OFCs or after introduction
at home. Dietary ingestion of products with extensively heated egg (baked egg, for example
as an ingredient in a muffin or cookie) was queried but was not considered evidence of
resolved egg allergy.
Dietary, medical and social histories were obtained using questionnaires completed during
enrollment interviews. A diagnosis of asthma and allergic rhinitis was based on parental
report or parental report of physician diagnosis. A diagnosis of other food allergies included
per protocol definitions for egg and peanut,
(16;18)
while for other foods this was based on a
clinical diagnosis by a study physician.
Diagnosis of baseline AD, in distinction to AD flares due to egg ingestion described above,
required pruritus and an eczematous rash (acute, subacute, chronic) with typical morphology
and age-specific patterns, a chronic or relapsing history, atopy (personal and/or family
history or IgE reactivity) and xerosis. AD severity was graded by criteria previously
described and published by Rajka and Langeland.
(19)
Briefly, the AD severity was graded as
mild, moderate, or severe (Supplemental Table E1) as described previously.
(18)
. Atopic
disease history in parents of the enrolled infants was based upon previously published
definitions and was recorded by parental report.
(20)
To maintain uniformity and an observational approach, the study design includes
evaluations, care for food allergy, and instructions on dietary management that were uniform
among the clinical centers, and reflect practice parameters in force at the time of enrollment
for AD,
(21)
food allergy,
(22)
and allergy prevention.
(23)
Participants were evaluated in person
at enrollment, 6 months, 12 months and yearly thereafter, with additional telephone follow-
up between each visit and instructions to contact the study site for any allergic reactions, at
which time additional details were obtained.
(10)
OFCs to egg were typically offered when
egg-specific IgE serum concentrations were ≤ 2 kU
A
/L and skin test mean wheal diameter
was < 10 mm if there was no reaction in the preceding 6 months. However, OFC was not
withheld if additional clinical data warranted OFC outside of these parameters (e.g.,
tolerance of a small accidental exposure or parental preference). OFCs were considered
positive for persistent subjective or for objective symptoms.
(24)
OFCs were performed with
cooked whole or pasteurized powdered egg, not raw egg white.
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Skin Prick Tests (SPTs)
SPTs were performed using the GreerPick® (Lenoir, NC) with participants avoiding
antihistamines for at least 5 half-lives of the specific agent. Tests were performed on the
infant’s back, and at 15 minutes the wheal was outlined in pen and transferred by tape to
paper. The size of the longest diameter and its longest perpendicular were averaged. A SPT
score was computed by subtracting the saline control measure and a positive SPT is defined
by a score of 3 mm or greater. Tests were considered reliable if the wheal of the negative
control (50% glycerin-saline) was 3 mm or smaller and wheal size of the histamine control
was at least 3 mm larger than the wheal size of the negative control. All sites used the same
lot of reagents, and training was performed to ensure consistency. The egg (chicken) white
extract was obtained from Greer (catalog number F272).
Serum egg-specific IgE and IgG4
The concentration of specific IgE antibody to egg white was measured from plasma at a
central laboratory (Mount Sinai) using the Thermo-Fisher ImmunoCAP® system (Uppsala,
Sweden) reported in kU
A
/L. A level >0.35 kU
A
/L was considered positive. The
concentration of IgG4 antibodies to milk were also measured from plasma samples using the
ImmunoCAP® system (detection limit 0.07 mg/L).
Mononuclear cell stimulation and PCR analysis
Studies were performed to determine if egg-specific Th2 or T regulatory cell gene
expression was predictive of egg allergy outcomes. Peripheral blood mononuclear cell
isolation was performed by Ficoll-Paque density gradient centrifugation and cultures were
performed at each clinical site on fresh venous blood samples as previously described.
(16)
Briefly, 4 million cells per condition were cultured for 48 hours in AIM-V serum-free media
(Invitrogen) with egg white protein (50 mcg each/ml), aqueous peanut extract (50 μg/ml),
tetanus toxoid (5 μg/ml), purified α, β, and κ-caseins (50 μg each/ml), and additional control
stimulations were performed with medium alone (negative) and anti-CD3/-CD28 beads
(positive). At the end of the culture period, cells expressing CD25 were enriched by
selection with anti-CD25 coated para-magnetic beads according to the manufacturer’s
protocol (Miltenyi). Pilot experiments demonstrated ~10-fold enrichment of CD25+ cells
with 70–80% of selected cells co-expressing CD3, CD4 and CD25 as measured by flow
cytometry. The entire selected fraction of cells was immediately lysed in RLT buffer
(Qiagen) and stored at −80°C until RNA purification. The quantitative polymerase chain
reaction (qPCR) was carried-out in the central laboratory according to the in-house
established protocol utilizing SYBR Green I fluorescence detection in a 384 well plate on
ABI 7900 (Applied Biosystems). Raw PCR analysis and annotation were performed on
coded samples. Threshold cycle number (Ct) was set by software with confirmation and
adjustment as necessary to define the threshold of linear amplification. For the gene
expression data, ddCt was calculated by subtracting the RPS9 reporter gene Ct and then
normalizing by subtracting the standardized medium control response. Negative values
indicate relatively higher activity with a unit score change corresponding to a doubling.
Non-detected genes were arbitrarily assigned a Ct of 40.
Statistical analysis
Time to resolution of egg allergy was measured with age as the time metric, whether
enrolled with egg allergy or having the diagnosis following enrollment. While the time of
allergy diagnosis varied depending on when food introduction and diagnostic testing were
performed, each individual’s first definitive diagnosis was positive for egg allergy.
Proportional hazards regression models were fit to examine covariates for their impact on
the hazard or risk function.
(25)
The estimated survival distribution was calculated from the
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relative hazard, which is the exponentiated sum of the linear combination of the products of
the parameter estimates with their respective clinical characteristics. The common
underlying empirical cumulative hazard function Lambda(t) is estimated with a step function
and the resolution curve is estimated as 1-exp(-RH*Lambda(t)). In this paper, hazard refers
to the chance of a beneficial event, i.e., allergy resolution, and variables are structured so
that large relative hazard values are associated with increased chance of allergy resolution.
A multivariate proportional hazards model was fit using significant baseline factors from the
univariate models to assess the probability of allergy resolution over time. The final model
was selected based on factor significance and model fit. Time varying clinical covariate
analyses used the most recent available assessment in the model and nonproportional
hazards were examined by fitting linear and spline function interactions with time. Reported
p-values are two-tailed when applicable and SAS 9.2 and R were used for the computations.
RESULTS
Of the 512 enrolled infants, the egg-allergic cohort consists of 213 children, of whom 140
were diagnosed with egg allergy at baseline. In the remaining 73, the diagnosis was
categorized as uncertain at their entry visit but egg allergy was subsequently confirmed at a
median age of 23.2 months (interquartile range, 16.1–41.9 months), 10 by OFC. Key
baseline characteristics are summarized in Table 1 and Table E2. AD was present in 196,
categorized as mild in 31, moderate in 104, and severe in 61. Twenty-seven infants (12.7%)
were diagnosed with egg allergy based on AD criteria while the remainder had a history of
an acute reaction and positive tests. Ninety-three subjects were first diagnosed based on a
reaction or clinical history that was limited to skin symptoms (hives, pruritus or swelling)
after exposure. Another 93 subjects were diagnosed based on a reaction that involved more
extensive symptoms (e.g., oral, upper/lower respiratory, GI or cardiovascular), in addition to
or apart from urticaria/angioedema.
One hundred five of the 213 participants (49.3%) have now resolved their egg allergy with a
median age of resolution of 72 months and a median age at last follow-up of 74 months
(Figure 1). Resolution was defined by OFC in 47 (44.8%) and by successful home
introduction of whole (not baked) egg products in the remainder, recorded by the time of
their visit. Regarding exposure to egg in baked goods, at the 6 year time point, 43 of 113
(38.1%) with unresolved allergy reported tolerating at least some baked egg products, while
4 reported reactions to ingestion of baked egg products.
Additional baseline characteristics of the cohort, comparing those with and without egg
allergy resolution, are presented in Table 1 and Cox regression analyses are shown in Table
2. The baseline characteristics that were most predictive of egg allergy resolution included
egg-specific IgE level and the characteristics of the presenting reaction. Specifically, highly
significant differences (P <0.001) in the rate of resolution were noted when comparing those
subjects with baseline egg-specific IgE levels <2 kU
A
/L, 2 – 10 kU
A
/L, and ≥10 kU
A
/L
(Figure 2). Significant differences (P = 0.007) in resolution were also predicted by reaction
classification, with those having acute reactions with only skin symptoms having a greater
likelihood of resolution compared to those with acute reactions involving systems beyond
the skin (Figure 3, distinguishing the 3 clinical categories described above). Those with an
AD flare from egg and those with systemic reactions to egg had poorer prognosis than those
with isolated urticaria/angioedema. The poor prognosis of the former reaction category may
be partly influenced by the requirement for elevated egg specific IgE antibodies in the
definition of an egg allergic reaction manifested by an AD flare. Resolution was also
associated with baseline AD severity (Table 2 and supplemental Figure E1), egg-SPT (Table
2 and supplemental Figure E2) and egg-specific IgG4 (Table 2 and supplemental Figure E3)
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