BACKGROUND
IgE-mediated tree nut allergy in children is common, often serious, and
usually lifelong [1]. Australia has the highest reported prevalence
of tree nut allergy [2-4]. Accidental ingestion is common, and nuts
are the most common trigger of fatal anaphylaxis in <20 year
olds [5-7]. Tree nut allergy resolution is very low, at around 10%,
[8] hence once established in young children, tree nut allergy is
usually life-long and avoidance remains the mainstay of management.
Systematic review and meta-analyses have shown that early peanut and egg
introduction reduces the risk of a child developing peanut or egg
allergy compared with delaying until after 12 months of age [9].
This has resulted in a paradigm shift in clinical practice, from advice
to delay the introduction of peanut and egg, to actively encouraging
introduction before 12 months of age. Accordingly, infant feeding
guidelines in Europe, Canada, the US and Australia have been revised to
recommend the introduction of peanut and egg (and in some countries
other common allergens) in the first year of life [10-12].
There are, however, no specific prevention strategies for tree nut
allergy. There is emerging evidence from the HealthNuts cohort,
which observed a protective effect of early cashew introduction with no
participants (0%: 95% CI, 0%-2.6%) who were introduced to cashew
before 12 months developing cashew allergy by 6 years of age [13],
compared to 3.6% (95% CI 2.9-4.4%) cashew allergy in infants who did
not consume cashew in the first year. Infants with peanut allergy are at
higher risk of developing tree nut allergies, with up to 40% of
children with peanut allergy developing one or more tree nut allergies
by age 6 [2, 14]. Of concern, the EarlyNuts study found that
parents of infants at high risk of tree nut allergy (peanut allergic
and/or eczema) were more likely to delay tree nut introduction compared
to infants without peanut allergy and/or eczema in the first year of
life [15].
Initial recommendations in the US suggested infants with peanut allergy
should be screened for tree nut allergies with tests of allergen
specific IgE sensitisation (skin prick test or serum IgE) and an
individual OFC performed for all sensitised tree nuts to determine
allergy status [16]. This approach may minimize parental anxiety and
assist with home introduction of the negative tree nuts but the concern
is the poor positive predictive value of IgE testing may mean a risk of
over diagnosis of tree nut allergy. Given long wait times and limited
access to hospital based OFCs, this approach may result in delayed
introduction of the sensitised tree nuts, potentially amplifying the
risk of developing additional nut allergies [17]. Given this, there
is a move towards recommendations against pre-emptive tree nut screening
for those with peanut allergy [10, 11].
The current practice in Australia is to advise infants with a diagnosed
food allergy to introduce all other food allergens one by one (including
tree nuts) via a cautious home introduction protocol without prior
allergy testing (screening). Whilst the risk of anaphylaxis in infants
via a cautious graded approach is considered low [17], there remains
the risk of IgE mediated reactions. Another concern is that it can be
labour intensive and time-consuming to introduce each of the 8
individual tree nuts (almond, brazil nut, cashew, hazelnut, macadamia,
pecan, pistachio and walnut) in a meal or ground form safe for infants.
We hypothesise a supervised multi-nut OFC (compared to home based
individual tree nut introduction) will reduce tree nut allergy
prevalence at 18 months of age in infants with peanut allergy,
facilitate earlier and ongoing ingestion of tree nuts, improve parental
anxiety and quality of life and reduce the healthcare costs associated
with the management of multiple nut allergies.
METHODS AND ANALYSIS