Discussion
In this study, we investigated factors associated with the clinical
course of egg allergy, with special focus on the disease–specific
QoL.19 The QoL was evaluated at the time of OFC, when
a threshold of safe consumption was determined for dietary advice, and
correlated with the 1–year outcome. We found that a better QoL at the
OFC was an independent predictor of an increased intake level of egg at
1 year after OFC, indicating that outgrowing egg allergy was associated
with the baseline QoL.
The mechanisms by which children naturally outgrow food allergy have yet
to be elucidated.21-23 Identification of clinical
factors that accurately predict the prognosis of food allergy may help
delineate the involved mechanisms.24 We performed a
systematic review of studies of the natural history of food allergy,
focusing on predictive factors for outgrowing an allergy. We used “food
allergy” AND “natural history” as keywords to conduct a Pubmed search
of original research articles in English, published from January 1963
through April 2020. This search yielded a total of 358 studies. We
excluded 263 studies dealing with irrelevant topics such as non-food
allergy, anaphylaxis and eosinophilic esophagitis. We also excluded 25
studies that did not deal with prognostic factors. Finally, we selected
70 studies that investigated factors involved in the natural history of
allergy to 3 food allergens (Figure S2).
Table S2 summarizes the factors that were reported to be negatively
associated with outgrowing a food allergy: high specific IgE, large
skin–prick–test reactions, systemic food–induced symptoms, history of
anaphylaxis, comorbid asthma and atopic dermatitis, a family history of
allergic disease, and multiple sensitizations (Table S2). Our present
study found that comorbid asthma and atopic dermatitis were
independently associated with not outgrowing egg allergy, which is in
agreement with earlier studies. In addition, we identified
disease–specific QoL as a predictive factor of food allergy outcome.
Although it was reported that the QoL of patients improved after they
underwent OFC, regardless of the OFC result,25 no
studies found an association between the QoL and the future food allergy
outcome. We believe that this is the first study to find the
disease–specific QoL to be a factor that may influence the natural
history of food allergy.
Food allergy is a serious burden for affected patients and their
caregivers because it requires strict performance of a variety of tasks,
including careful cooking/eating to avoid the offending allergen, causes
anxiety over the risk of anaphylaxis, and limits common social
activities associated with eating. Thus, the parents of children with
food allergy were reported to have a poorer general QoL than the parents
of normal children.26 The health–related QoL of
children and adolescents with food allergy was shown to be worse than
not only that of the general population but also that of type 1 diabetes
patients.27 Our present results indicate that a poor
QoL is not only a consequence of the child’s food allergy but also a
factor that possibly influences the future status of the child’s
disease.
In fact, a prospective study that assessed the nutritional attitudes of
children with food allergy before and after OFC in relation to their
mothers’ anxiety showed a negative correlation between anxiety of
mothers before OFC and degree of change in nutritional habits of their
children after OFC.18 The authors stated that a
positive attitude of mothers toward food before OFC promoted subsequent
food reintroduction, which increased children’s interest in tasting new
foods, and led to favorable changes in nutritional habits. A negative
initial maternal attitude, on the other hand, led to an unfavorable
attitude in the child.18 Likewise, in our present
study, a better QoL—which is partly equivalent to less anxiety—may
have led to the child having a positive attitude toward food and an
increase in egg intake. This tendency was observed regardless of both
the OFC results and the severity of egg allergy, represented by the
specific IgE level. Since intake of a small amount of an allergenic food
after a negative low–dose OFC was reported to increase the intake
threshold,28,29 a better initial QoL may promote
outgrowing the allergy.
We also found that the initial QoL for the outgrowing patients further
improved 1 year after the OFC, whereas the QoL for the non-outgrowing
patients remained unchanged or became worse. The QoL of food allergy
patients was reported to be worse in older children, probably because of
a long period of food avoidance and an increasing demand for social
activities involving food.30,31 Conversely, a negative
OFC32 and oral immunotherapy33 were
associated with a better QoL. Our results are consistent with those
earlier reports.
This study has at least 3 limitations. First, we used a questionnaire to
determine the daily amount of egg consumed at 1 year after OFC, rather
than repeat the OFC. However, the threshold determined by OFC does not
always reflect a patient’s actual eating habits. We believe that the
caregiver–reported actual intake is more clinically relevant than an
“experimental” OFC threshold. Second, the number of subjects was
relatively small, and the statistical power to identify prognostic
factors was thus not strong. Third, we followed up the patients for only
1 year and evaluated only the trend toward outgrowing egg allergy, not
actual achievement of that goal. Further studies are needed to confirm
our present findings.
In conclusion, we found that a better QoL at baseline was associated
with a child’s outgrowing egg allergy, while vice versa, a poorer QoL
was associated with delayed resolution. A caregiver’s psychological
status, partly expressed as the disease–specific QoL, may have an
impact on the child’s food allergy outcomes. Intervention focusing on
the child’s baseline QoL may lead to better management of food
allergies.