Childhood Anaphylaxis in Asia

Whether childhood food allergy (FA) has increased in recent years continues to be a potential source of debate [1]. Demand for allergy-related medications and anaphylaxis-related hospital services have steadily increased in recent decades in many high-income countries [2, 3]. By contrast, population-based studies of food sensitization, fatal food anaphylaxis rates or challenge-confirmed FA demonstrate inconsistent evidence of increase [1-3]. The perception that childhood FA incidence may have increased over the last three decades is largely underpinned by data derived from changes in hospital emergency room use and admission rates for treatment of anaphylaxis, and to a lesser extent, demand for outpatient services [2, 3]. Most studies show an acceleration in anaphylaxis hospital presentation and/or admission rates in the last two decades, with the highest burden falling on young children aged 0–4 years. Significant country-to-country differences in estimated FA and anaphylaxis prevalence rates and common food triggers have been described, with lower rates previously observed in Asia compared to other regions [4].

That situation, however, may be changing. In this issue, Goh et al. describe an approximate doubling in hospital presentations coded as anaphylaxis in those aged 0–19 years in Singapore from 2015 to 2022 [5]. Rates quadrupled in those aged 0–4 years, mirroring patterns previously reported from high-income countries outside of Asia. There was a parallel increase in anaphylaxis admission rates but no overall increase in severity, as assessed by the presence of shock, doses of adrenaline required or the need for higher levels of care [5]. The authors also reported no overall increase in attendances for total “allergy-related” presentations from 2015 to 2019; the rise was only seen for presentations coded as anaphylaxis. There were also no changes in total emergency room attendances for all medical or trauma cases, suggesting the trends observed were not an artefact of higher presentation rates overall. Adrenaline was administered in 88% of cases. Ethnic variation was observed, with higher presentation rates noted in the 24% of the population without Chinese/Malay ethnic background. Consistent with studies from high-income countries outside of Asia, the highest rates occurred in children aged 0–4 years, with the increase predominantly driven by allergy to egg, peanut, tree nuts, dairy products and shellfish. Their most recent rates of 38.8/10⁵ population is comparable with those described in Europe, and Northern America/South West Pacific countries [3, 4], albeit this increase occurring a decade after similar observations in these other regions.

A small number of studies suggest that FA/anaphylaxis presentations may be increasing in Asia in line with other countries. Even within Asia, there is significant heterogeneity in estimated rates of anaphylaxis, with the lowest rates observed in Qingdao in mainland China (1/10⁵ population/year), followed by Hong Kong (11/10⁵), Singapore (21/10⁵) and Thailand (21–25/10⁵) [6]. Shellfish was the major trigger in all countries, but curiously peanut allergy was reported as absent in Qingdao and Thailand. While the study by Goh et al. was not designed to examine risk factors for this increase, other studies describe the highest rates of FA/anaphylaxis in the most urbanized and population dense centres of Asia. This may reflect a so-called ‘westernized lifestyle’, associated with dietary habits, composition of gut microbiota, socio-economic status, city versus rural residency but in Asia, not necessarily exposure or timing of introduction of common allergenic foods [5, 6]. One needs to acknowledge the many potential caveats associated with use of hospital-derived data in these studies [5, 6], such as coding errors, anaphylaxis treatment guidelines and hospital admission policies, difficulty differentiating between unique or multiple presentations by the same individual, changes in patient health-seeking behaviour, availability of community care, more effective anaphylaxis treatment in the community or availability of adrenaline autoinjectors for self-administration. Furthermore, there are a few ways of interpreting higher rates of anaphylaxis presentations without higher rates of severity in this Singapore-based study. These include one or more of (a) changes in health seeking behaviour, with milder cases seeking medical attention (instead of recovering at home); (b) a lower threshold by hospital staff to classify allergic-like presentations as anaphylaxis; (c) a change in the nature of FA severity itself (albeit unlikely); or (d) the very high rates of adrenaline use, shown in other studies to reduce the need for admissions and further adrenaline doses, as described here (1.9% vs. 7% international average).

Perceptions of changing epidemiology of childhood FA have driven trials to reduce the risk of new FA (e.g. changes in maternal diets, hypoallergenic formula and dietary supplements) with generally disappointing results [7]. Timing of early allergic food introduction is one potentially modifiable risk factor, but its impact is potentially impeded by incomplete adherence rates even in controlled trials [7], and may not be of benefit in countries where FA incidence is low [8] or perhaps in some ethnic groups such as those of East Asian ancestry [8, 9]. Even if weaning guidelines are eventually shown to reduce the risk of new FA in young Asian infants, barriers to implementation are numerous. These include the need for early and regular consumption of allergenic food, a practice potentially influenced by cultural values, simplicity of implementation, health literacy, lack of incentive for a prophylactic intervention in the absence of known allergy (or fear of doing so in the opposite situation) or perhaps even lifestyle choices such as vegan diets. In that context, the dramatic impact of controlled studies is yet to be seen in a definite drop of FA/anaphylaxis thus far. Nonetheless, some encouraging signals have been observed in systematic reviews of early dietary diversity, changes in anaphylaxis hospital admission rate trends (several studies) or non-significant challenge-proven decreases in early childhood peanut allergy in Melbourne since weaning guidelines were changed in 2016 [9].

Regardless of the potential interpretation of their data, at a minimum, the study by Goh et al. demonstrates a higher demand for FA/anaphylaxis health care spanning less than a decade, with downstream implications for providing community and health professional education on recognition and management, demand for specialist services, costs of care and the need for further research to help explain regional disparities in rates and specific food triggers.

The author declares no conflicts of interest.