Childhood food allergy in the New Zealand context: An exploration of trends, prevalence, risk factors, and the impact on quality of life

Abstract

Although food allergy has been extensively described, diagnosed, managed and researched, many questions still linger. For over 2000 years scientists have sought to understand the effects of food on the human body. Hippocrates, the Father of Medicine, had recognition that food can cause illnesses, disease and health concerns for some people. In 1906, Dr Clemens von Pirquet suggested the use of the word “allergy” to describe an inappropriate reaction to food or other substances not typically harmful or bothersome. Researchers are just beginning to recognise potential influences on the development and progression of food allergy. The prevalence and incidence rates of food allergies worldwide have been the subject of much debate in recent decades due to what many observe as a dramatic increase in childhood food allergies. A food allergy touches the life of not only the individual diagnosed but also their family, friends, health care providers, food producers, retailers, and schools. The epidemiology of food allergy in New Zealand has been incompletely described and there is minimal published data that allows for any estimation of the disease burden caused by food allergy in New Zealand. Aims Although New Zealand has a high prevalence of asthma, the epidemiology of other atopic disease has not been studied. Based on other studies completed around the world and the data available in New Zealand this thesis set out to better understand: (1) temporal trends in food allergy; (2) prevalence of peanut allergy and risk factors for peanut allergy; and (3) the impact of childhood food allergy on quality of life. Methods To meet the objectives of this thesis four projects made up of five studies were completed. Each project utilised a different data set to allow comparisons to be made of data from New Zealand with that which has been reported from other countries and to provide several perspectives on how food allergies are impacting New Zealand children. 1) To determine whether Emergency Department presentations can be used to describe temporal trends in food allergy presentations an audit was completed for all emergency department (ED) presentations from 1988 to 2011 of children (0 to 14 years old) to the public hospital ED in the Auckland District Health Board (ADHB) region, for which the ICD codes ‘anaphylaxis, unspecified’ or ‘allergy, unspecified’, were assigned. 2) The new knowledge learnt from project one was then applied to the National Minimum Dataset (NMDS), a national collection of public and private hospital discharge information, temporal trends in emergency department (ED) presentations for food-related acute allergic reactions from 1988 to 2011 of children (0 to 14 years old) were investigated. 3) Utilising data from the Growing Up in New Zealand cohort study the prevalence of peanut allergy and factors associated with the presence of peanut allergy at age two years were investigated. 4) The impact of food allergy on quality of life was investigated through the use of reflexive photography, photo elicitation, and the autodriven interview with food allergic children and their families. Results Understanding Administrative Coding of Emergency Department Visits for Unspecified Acute Allergic Reactions The aim of this project was to determine the proportion of ED visits coded as ‘anaphylaxis, unspecified’ or ‘allergy, unspecified’ that are food-related allergic reactions. Food-related acute allergic reactions account for 29% of hospital presentations that were assigned a discharge code for ‘anaphylaxis, unspecified’ or ‘allergy, unspecified in the ADHB. The ED presentation rate with food-related allergic reactions from 2004-2011 was almost twice as high as that which occurred from 1988-1995 (RR=1.98, 95%CI 1.10-3.72). By contrast, ED presentation rates for non-food-related allergic reactions did not change over these years. This apparent increase in New Zealand is consistent with observations using comparable data sources reported from Australia and the United States. Hospital Presentations Due to Acute Allergic Reactions Related to Food Between 1988 and 2011, 3,735 children 0 to 14 years old presented to a New Zealand hospital with an acute allergic reaction identified by ICD-9-CMA-II codes 692.5 (contact dermatitis and other eczema due to food in contact with), 693.1 (Dermatitis due to food taken internally), 995.0 (Anaphylactic reaction due to unspecified food), 995.3 (Allergy, unspecified), and 995.60-995.69 (Anaphylactic reaction due to food unspecified and specified). An average yearly increase of 8% in hospital presentations due to acute allergic reactions (p=<0.001) was observed. In comparison to the 1988 time interval (annual rate 7.11/100,000), the rate of all acute allergic presentations was consistently higher from 1997 onwards with rate ratios increasing from 1.43 and 1.55 in 1997 and 1998 to 6.06 and 5.33 in 2010 and 2011. Over the time interval from 1988 to 2011 there has been an average yearly increase of 9% in hospital presentations due to all of the identified acute allergic reaction diagnostic groups (p<0.001). A greater rate of increase was observed in the anaphylactic and allergic reactions group (average increase 11% per year, p<0.001) as compared to the skin related group (average increase 2% per year, p<0.001). Peanut Allergy in the New Zealand Context Based on parental reported data collected from Growing Up in New Zealand, a contemporary longitudinal birth cohort study, 162 (2.1%) children were identified as peanut allergic. Within this cohort, factors associated with the development of a peanut allergy were categorized based on the measurement of child, family & wider influences on disease in early childhood as defined by: child characteristics, proximal social environments, distal social environments, and macro environmental factors. The odds of having parental reported peanut allergy at age two years were increased for boys, children diagnosed with eczema since 9 months, children whose mother had a history of atopic disease (eczema, hay fever, or food allergy), and mothers who identified as being of Asian ethnicity. The odds of having parental reported peanut allergy at age two years were decreased for children who had never tried nuts or peanuts, or whose mothers had no secondary qualifications or secondary school/NCEA 1-4. Impact of Food Allergy on New Zealand Families The impact a food allergy has on a family is influenced by environment and includes four levels home, school, community, and beyond the community. This is due, in part, to the amount of control a food allergic family has within these environments. The ability to control the environment gradually decreases as a food allergic family moves away from the home. Based on the impact a food allergy has on the food allergic family, three outcomes of living with a food allergy are evident responsibility, exclusion, and resilience. The lessons learned from these families can be used to guide other food allergic families through education and advocacy. Based on the family’s description of the impact of a food allergy on their quality of life and management strategies, there is a need for consistent national school policy focused on food allergies and the provision of education and training to hospitality workers. These changes could positively impact food allergic families at multiple environmental levels. Discussion Consistent with what has been reported from several other countries the prevalence of childhood food allergy appears to have increased in recent decades. The rate of parental self-report of peanut allergy in New Zealand is similar to other countries. In New Zealand, children of male gender or who have eczema are at increased, and those who have never tried nuts or peanuts by age two years were at decreased risk of parental reported peanut allergy. In New Zealand children of atopic mothers or mothers of Asian ethnicity are at increased risk and children of less educated mothers are at decreased risk of parental reported peanut allergy. A food allergy impacts all members of a food allergic family based on the level of control within various environments. Food allergy is a complex condition and this thesis provides insight into the current state of food allergy in New Zealand.