Introduction
The incidence of anaphylaxis has continued to rise globally based on
hospitalised data from Europe, United states, Australia, Brazil and some
Asian countries such as South Korea and Taiwan [1, 2]. However, the
actual incidence is likely to be several folds higher due to
mis-diagnosis, mis-classification, due to under reporting [1] and
also because allergies and anaphylaxis being neglected in many
developing countries, due to other disease priorities [3]. Food
allergy was shown to be the predominant cause of anaphylaxis, followed
by drugs and venom, in many countries [1, 2, 4]. However, in a large
proportion of cases, even after extensive evaluation, a trigger cannot
be identified, and such cases are classified as ‘idiopathic
anaphylaxis’[5].
Approximately 10% of children and 30 to 60% of adults presenting with
anaphylaxis are classified as having idiopathic anaphylaxis (IA), as a
trigger cannot be identified [5]. Mast cell disorders such as
mastocytosis, mast cell activation syndrome and hereditary
α-tryptasaemia, are some of the conditions that can cause IA, and
screening for these diseases have been suggested in the diagnostic
work-up [6]. Allergy to Galactose-α-1,3-galactose (α-gal), has shown
to be important cause of anaphylaxis in those in whom a cause cannot be
identified [7]. Alpha-gal allergy typically occurs 3 to 6 hours
after ingestion of red meat and has shown to occur due to IgE antibodies
specific to the carbohydrate epitope found on mammalian meat [8].
Since the identification of α-gal allergy as an important cause of
delayed anaphylaxis, screening for the presence of allergy to α-gal has
been included in the diagnostic workup in a patient, in whom a possible
cause of anaphylaxis cannot be identified [7]. Other important
causes where IA was shown to be food dependent exercise induced
anaphylaxis (FDEIA), due to presence of IgE to omega-5-gliadin [5].
FDIEA, has indeed shown to be an important cause especially in patients
who present at specialised allergy clinics. In one study, 12.2% of
patients were identified as having FDIEA [9].
Although the incidence of anaphylaxis is not reported in many lower
middle-income countries (LMICs), the incidence of asthma and asthma
related mortality has shown to be rising [10]. Diseases related to
allergies are neglected in many LMICs with adrenalin not used in many
instances, in the management of anaphylaxis and long-term management of
patients with anaphylaxis being sub-optimum due to the non-availability
of adrenalin autoinjectors [3, 11]. Although there is no data on the
incidence of anaphylaxis and other allergic diseases in Sri Lanka, there
is a high prevalence of asthma and allergen sensitization reported among
Sri Lankan children [11, 12]. Furthermore, many patients with
anaphylaxis present to specialised allergy clinics in Sri Lanka where
food allergy, FDIEA and allergy to vaccines have been identified as the
predominant causes of anaphylaxis [9, 13, 14]. As food consumption
patterns, genetic background, and environmental factors can lead to
differences in allergen sensitization patterns in different geographical
regions, we sought to identify the possible triggers of IA in Sri Lankan
patients presenting to specialised allergy clinics in Sri Lanka.