Paediatric food allergy trends in a community-based specialist allergy practice, 1995–2006

Australia has one of the highest prevalences of allergic disorders in the developed world. Recent decades have seen increases in the prevalences of allergic rhinitis, asthma and atopic eczema (although the proportion of people with asthma has plateaued in the past few years).1,2 Evidence that food allergy is becoming more common, however, is limited to changes in prevalence of peanut allergy in two separate studies of young children, which showed a doubling of clinical reactivity over 5 years.3,4

In the absence of comparable epidemiological studies of food allergy in Australian children, a dramatic increase in the number of young children referred to me for evaluation of food allergy and food-associated anaphylaxis (FAA) prompted me to compare my clinical practice with Australian hospital admissions data to determine whether this was a practice-specific or region-specific phenomenon, or was generalisable to the Australian population.

Data were analysed for patients aged 0–5 years who were referred to a community-based specialist immunology/allergy medical practice in the Australian Capital Territory (population about 0.33 million) from 1 January 1995 to 30 December 2006. John James Memorial Hospital Ethics Committee approved the study.

This study identified a 12-fold increase in demand for consultations related to food allergy (and a sevenfold increase in FAA) in children over a 12-year period in a single private practice providing approximately 50% of specialist allergy-related ambulatory services in the ACT. The number of anaphylaxis-related hospital admissions in Australia also increased over the same period, and this increase was disproportionate in children with FAA.

I studied children aged 0–5 years because of a disproportionate increase in demand for assessment for food allergy in this age group. Time trends were not an artefact of practice expansion, triaging, change in local medical services or ACT demographic changes. The practice casemix (not total workload) changed — there was no triaging, relevant ACT medical services actually expanded, and ACT birth rates and the number of children aged 0–5 years fell about 10% during the study period (Maureen Bourne, Data Manager, ACT Maternal and Perinatal Data Collection, Canberra Hospital, personal communication). That similar demand for assessment of patients for food allergy has been observed in Canberra Hospital clinics (Dr Carolyn Hawkins, Department of Clinical Immunology, Canberra Hospital, personal communication) suggests that changing demand is not simply a practice-specific phenomenon.

There are limitations to a single-practice study. I was able to examine a subset of patients seeking medical assessment, but not a random selection of the entire population. The effects of the natural evolution of practice casemix with time, practice reputation, referral bias, increased recognition that food allergy could both aggravate and coexist with atopic eczema, and the drift of patients from other subspecialties (eg, paediatrics) must be considered. Furthermore, increased service demand is not equivalent to increased prevalence, which requires confirmatory evidence.

The dramatic increase in hospital admissions for anaphylaxis in Australia (around twice that described in United Kingdom studies10,11) is independent of both referral bias and location, and has been interpreted as evidence of a food allergy/FAA “epidemic” in some quarters.12 Admission rates, however, can be influenced by service availability, lowered threshold to seeking medical assistance (perhaps reflecting parental anxiety or perhaps even anaphylaxis management plans7), or changes in medical practice to lower the threshold for admission. Contrary evidence counters these interpretations, showing that emergency management plans reduce anxiety, the risk of relapse and need for medical intervention.13 Other studies have shown that only a small proportion of children presenting with food allergy/FAA are admitted to hospital,14 suggesting that patients with relatively minor symptoms are more likely to be coded as having urticaria (and discharged) than having anaphylaxis (and admitted). Even if hospital coding errors occurred, these are likely to have transferred patients between diagnostic categories for manifestations of allergy (eg, ana-phylaxis, acute urticaria/angioedema), and the number of patients in all these diagnostic categories increased. Nor are the data a statistical artefact — identical age-specific admission-rate time trends emerged using both ABS estimated population and census data. Overall, the data suggest that changes in admission rates reasonably reflect changing prevalence of FAA in infants.

Measuring demand for allergy-related medication is a less useful measure of changing prevalence. Hypoallergenic infant formula prescriptions increased fourfold in the 5 years ending 2004.15 Significant regional variation in prescribing rates could also reflect increased awareness, access to specialist services, or inappropriate prescribing. While sales of the EpiPen autoinjector (CSL Limited, Melbourne, Vic), which delivers adrenaline as first aid for severe allergic reactions, have increased substantially in recent years16 (and well before the introduction of Pharmaceutical Benefits Scheme subsidies in 2003), it is impossible to assess the relative distortions introduced by routinely providing two EpiPens to children, EpiPen-prescribing guidelines introducing asthma as a factor to be considered when evaluating those with food allergy (not necessarily anaphylaxis8), inappropriate prescribing and, possibly, medicolegal pressures.

Estimates of disease burden, prevalence and time trends for allergic disorders have been based (in part) on health service use in other studies.10,11,17 Unfortunately, it is difficult to quantify the effects of factors such as changes in health-seeking behaviour, driven (in part) by increased community awareness or by anxiety induced by recent media reports of fatal FAA,18 on apparent changes in the prevalence of allergy. The adoption of government policies on food allergy/FAA management in schools and childcare centres (adopted in South Australia in 1998 and the ACT and New South Wales in 2003) may not only reflect community concerns, but also drive demand for children to be assessed for food allergy before enrolment, which might partially explain the greater increase in consultations related to food allergy compared with FAA. Assuming that behavioural factors were the only explanation, however, would presuppose a large cohort of previously unassessed children with food allergies, many with anaphylaxis, and would not explain the similar trends observed in older age groups, both in terms of consultations and hospital admissions.

Rapid increases in disease prevalence over a decade are not unprecedented.2 Given the documented relationship between food allergy and infantile atopic eczema,19 it would be surprising if the prevalence of food allergy had not also increased in parallel with the almost doubling of the prevalence of atopic eczema documented between 1993 and 2002 in Australian children.2 Increases in food allergy/FAA-related consultations and admissions for infants (disproportionate to population size) would not be unexpected if food allergy is becoming even more prevalent in this “sentinel group” in which it is already most common. In the context of Australian and UK admissions data and increased incidence of food allergy in two well conducted population studies,3,4 it is difficult to escape the conclusion that, while anxiety has probably contributed to service demand, the underlying prevalence of food allergy has also increased in Australian infants over the past decade.

This study was not designed to explain the changing prevalence of food allergy. Hypotheses (for which there is limited published evidence) include greater exposure to potentially allergenic foods, sensitisation to topical allergens in emollients, increased use of antacid medication in infants, sensitisation through breast milk, prolonged breastfeeding, and increasing maternal age.20-23 If the data are confirmed to represent an actual increased prevalence of food allergy, long-term implications include: (i) a need for more resources for evaluating and re-evaluating patients; (ii) an eventual increase in the incidence of food allergy in older people in whom mortality is more common; and, possibly, (iii) a need to reassess the risk of fatal outcomes in young children if the underlying problem is more common.18

There is an urgent need for coordinated systematic studies of the epidemiology of food allergy in Australia and abroad, to ascertain risk factors and guide public health policy. If such studies confirm an increased prevalence of food allergy, there are important implications for public health, medical workforce planning, costs of care and the availability of public allergy services in Australia, that are currently deficient in some regions such as the Northern Territory, Tasmania and Queensland.

1 Time trends in allergy-related disorders in children aged 0–5 years referred to an Australian Capital Territory private practice

2 Trends in hospital admission rates for selected allergy-related disorders in the financial years 1993–94 to 2004–05*

* From Australian national hospital morbidity data.9 † Rate per million population.

3 Age-adjusted Australian hospital admission rates for anaphylaxis in the financial years 1993–94 to 2004–05

* Rate per million population.