The Longitudinal Study of Australian Children
Annual statistical report 2012

8 Children's food allergies

Nadine Bertalli and Katie Allen, Murdoch Childrens Research Institute, The Royal Children's Hospital

Brigit Maguire, Australian Institute of Family Studies

Download printable version: 8. Children's food allergies (PDF 583 KB)

8.1 Introduction

The "allergy epidemic" is a major public health issue predominantly facing Western countries, including Australia. There has been a rapid increase over the past 30 years in the prevalence of allergic conditions such as asthma, eczema and food allergy, and the causes remain unknown. Food allergy prevalence in particular, has increased dramatically over the past decade. Most concerning is that food allergy is a problem that affects mainly children (Sicherer, 2011).

The disease burden of childhood allergic conditions is substantial. Around 25% of Australian children have asthma or asthma-like symptoms (Asher et al., 2001, 2006), 20-24% have eczema, and 15-25% have allergic rhinitis (Beasley, 1998). The prevalence of childhood food allergies, however, is less certain. A recent meta-analysis using data from Europe and North America determined that between 12% and 13% of children aged 0-16 years reported food allergy symptoms, and food challenge tests1 confirmed a prevalence of 1-11% (Rona et al., 2007). Australian population-based research has shown that up to 10% of infants have confirmed food allergies (Osborne et al., 2011). Although there is uncertainty about the exact prevalence of food allergies, research suggests that it is increasing. For example, in the United States, the rate of food allergies has been shown to have increased 18% from 1997 to 2007 (Branum & Lukacs, 2009), while peanut allergies doubled, from 0.4% in 1997 to 0.8% in 2002, and more than trebled to 1.4% in 2008 (Sicherer et al., 2010). Hospital admissions for food allergies and anaphylaxis (swelling/breathing difficulties) have seen similar rises in both the United Kingdom and Australia. In the UK, a seven-fold increase was observed in the period 1990-91 to 2003-04 (Gupta, Sheikh, Strachan, & Anderson, 2007), and in Australia, a 350% increase was seen in the period 1994-95 to 2004-05 (Liew, Williamson, & Tang, 2009).

Around 85% of children with an early allergy to foods - including eggs, cow's milk, wheat and soy - will develop tolerance to these foods by age 5 years (Wood, 2003). Allergies to peanuts and tree nuts, on the other hand, are typically lifelong. Only 20% of children with a peanut allergy and 9% of children with a tree nut allergy outgrew these allergies by the time they reached school (Fleischer, Conover-Walker, Matsui, & Wood, 2005; Ho et al., 2008).

Adverse food reactions can cause physical symptoms ranging from the mild (e.g., hives) to the severe (e.g., breathing difficulties); however, not all food reactions are food allergies. A food allergy causes adverse physical symptoms and involves the immune system. A food intolerance, on the other hand, does not involve the immune system. Survey questionnaires are unlikely to be able to reveal whether respondents recognise this difference.2

Food allergies can be classified as being "immunoglobulin E (IgE)-mediated" or "non-IgE mediated", based on a person's food reaction history/food challenge (using time to onset of reaction and symptoms) and from allergy test results (see Table 8.1; Allen, Hill, & Heine, 2006).

Table 8.1: Classification of IgE- and non-IgE mediated food allergies
Group 1 Group 2 Group 3
Time to onset of reaction < 1 hour 1-24 hours > 24 hours
Ingested volume required for reaction Small Moderate Large
Symptoms Immediate food hypersensitivity, urticaria, erythema, angioedema, vomiting, anaphylaxis Vomiting, diarrhoea, colitis, functional intestinal obstruction Diarrhoea, atopic dermatitis, failure to thrive, gastro-oesophageal reflux, severe infantile colic
Syndromes Oral allergy syndrome Food protein-induced enterocolitis syndrome Food protein-induced enteropathy, enterocolitis and proctocolitis; multiple food allergy
Immune class IgE-mediated Mixed IgE- and non-IgE mediated Non-IgE mediated
Immunological characteristics Large wheal on skin prick test, raised levels of food-specific serum IgE antibodies Not known Enhanced T-cell reactivity

Notes: Medical terms: Urticaria - red itchy bumps on the skin, also called hives. Erythema - redness of the skin. Angioedema - swelling below the surface of the skin.
Food protein-induced gastrointestinal syndromes are allergic reactions and non-IgE gastrointestinal reactions are believed to be delayed allergic reactions, following ingestion of one or more foods. Symptoms affect various parts of the gastrointestinal tract. Specific syndromes are: Food protein-induced enteropathy - inflammation of the small intestine; symptoms include diarrhoea and failure to thrive. Food protein-induced enterocolitis syndrome - inflammation of the small and large intestine; symptoms include profuse diarrhoea, vomiting, dehydration and failure to thrive. Food protein-induced proctocolitis - inflammation of the lower section of the large intestine; symptoms include low-grade rectal bleeding.

Source: Allen et al. (2006)

In an IgE-mediated reaction, food-specific IgE antibodies (a type of marker produced by the immune system to identify foreign substances) "recognise" when the food is eaten and activate the immune system's inflammatory response. IgE-mediated reactions usually occur within minutes of ingestion of the offending allergen and most often result in hives, angioedema (swelling) of the face or vomiting. IgE-mediated food allergy is associated with the most serious form of food allergy - anaphylaxis - which can be fatal if left untreated. Anaphylaxis is a multi-system, rapidly evolving allergic reaction that involves respiratory and/or cardiovascular compromise (Allen et al., 2006).

Non-IgE mediated food allergies occur via a different, as yet undetermined, mechanism in the immune system. The majority of non-IgE mediated symptoms are delayed until more than four hours to days after ingestion, and are generally gastrointestinal in nature (e.g., diarrhoea and vomiting). Little is known about common precipitants of non-IgE mediated food allergies since there have been no population studies and few clinical cohort studies of these conditions using formal food challenges. However, typical foods thought to be common causes of non-IgE mediated food allergy include cow's milk and soy and, to a lesser extent, wheat. Non-IgE mediated food allergies to peanut and tree nuts have not been reported.

Medical assessment of a suspected food allergy involves a thorough investigation of food ingestion, reaction and medical history and, where appropriate, allergy testing. In a skin prick test, the skin is pricked with a needle containing a drop of food allergen. In children sensitised to the food, a small bump or wheal will develop. A blood sample can also be drawn to test for IgE levels. A food challenge - in which the suspect food is fed to the child and any reactions observed - is the most accurate way to diagnose a "true" food allergy. A food challenge may be undertaken either to diagnose a food allergy (typically in younger children), or to test for tolerance (typically in older children who are suspected of having outgrown their food allergy), but generally only if the child's history is uncertain or if he/she is at an age where tolerance would be expected to develop.

A diagnosis of a food allergy can affect the quality of life of not only the child but also their family, their school and community. Food-allergic children and their carers need to be vigilant to avoid ingesting allergenic foods, particularly in social and school environments. They may also need to carry an adrenaline auto-injector (for those at risk of anaphylaxis) and generally live with the fear of having an adverse reaction to food (Bollinger et al., 2006; Marklund, Ahlstedt, & Nordstrom, 2007; Sicherer, Noone, & Munoz-Furlong, 2001).

8.2 Risk factors for food allergy

It is widely accepted that gender and co-existent atopic disease (allergic diseases such as asthma, hay fever or eczema) are associated with the incidence of food allergy. In a review of population-based studies, Sicherer (2011) observed that male children and adult women were at increased risk of food allergy compared to the rest of the population. The same research also found that food allergy was positively associated with co-existent atopic disease and that asthma was a risk factor for increased severity of food reaction. The search for other factors to explain the rise in food allergies has been less clear and has often been explored in relation to allergic diseases in general rather than food allergies specifically.

Early life factors - such as birth weight, prematurity, breastfeeding and the timing of the introduction of solids - have been investigated as risk factors for the development of allergy. In a recent review, prematurity and/or low birth weight were not found to be associated with childhood food allergy and were protective against atopic dermatitis (Pali-Schll, Renz, & Jensen-Jarolim, 2009). A review of the role of breastfeeding in the development of allergic diseases concluded that there were insufficient data on the role of breastfeeding in the development of food allergies, inconclusive evidence in regard to eczema and inconsistent data with regard to asthma (Matheson, Allen, & Tang, 2012). Several studies included in a review by Cochrane et al. (2009) found that the delayed introduction of solid foods is associated with a higher risk of allergic diseases, including food allergy.

One Australian study, using publicly available national databases, examined the role of socio-economic position (SEP) and area of residence on the risk of childhood food allergy. The authors found that having a higher socio-economic position and residing in urban areas were risk factors for childhood food allergy and anaphylaxis (Mullins, Clarke & Camargo, 2010).

Low vitamin D has recently been hypothesised as being a risk factor for food allergy and other atopic diseases. Two large population-based studies have supported this hypothesis, with one measuring serum vitamin D (Sharief, Jariwala, Kumar, Muntner, & Melamed, 2011) and the other using geographic latitude as a proxy measure of vitamin D (Osborne, Ukoumunne, Wake, & Allen, 2012).

This chapter uses the Growing Up in Australia: The Longitudinal Study of Australian Children (LSAC) data from Wave 4 for the B cohort (6-7 year olds) and K cohort (10-11 year olds), with some background information also taken from Waves 1 and 2 where necessary. The strength of these data is that they allow for a whole-of-population analysis across two childhood age groups.

This chapter aims to:

  • describe the prevalence of food allergy - assessed via history of food reaction and results of food allergy testing - by food allergen and age group;
  • describe the timing of and symptomology of food reaction, by food allergen and age group; and
  • assess the relationship of demographic/antecedent factors - urbanicity, vitamin D levels (as measured by latitude and sun exposure), gender, socio-economic position, duration of breastfeeding, timing of the introduction of solids, birth weight and gestational age - on food allergy status (probable food allergy, probable food intolerance, and no food allergy/intolerance).

The methodology of each of the outcomes and risk factors is described alongside the tables in the results section.

8.3 Prevalence and characteristics of food allergy in children

The prevalence of self-reported food reactions are known to be higher than the prevalence of diagnosed food allergy (Venter et al., 2006, 2008). Parents were asked whether their child had ever had a reaction (such as redness or itching) that they thought was due to food that the child had eaten. It was found that 15% of the B cohort (667 children) and 12% of the K cohort (526 children) had had such a reaction. In the younger cohort, the rate was slightly higher than the 12-13% reported by an international review of children 0-16 years old (Rona et al., 2007) and the 12% determined in a sample of 6-year-old children in the UK (Venter et al., 2006).

For those children who had had a reaction, parents were then asked what food caused the reaction. For each food type, they were then asked how old the child was when they first had a reaction to the food. Table 8.2 details the mean age at first food reaction by type of food allergen, among those who had ever had a reaction, for each age cohort.

Table 8.2: Age at child's first food reaction, by food allergen, children who had had a food reaction, B and K cohort, Wave 4
Allergens B cohort K cohort
Percentage No. of observations Mean age at first reaction (months) Percentage No. of observations Mean age at first reaction (months)
Peanuts 17.6 114 21.3 16.0 81 28.7
Other nuts 9.1 61 28.6 9.3 43 42.5
Eggs 14.9 97 15.6 9.1 47 24.0
Cow's milk 12.2 87 15.1 10.6 61 20.5
Soy 2.8 19 23.4 2.1 10 18.4
Sesame 1.8 13 31.3 0.3 2 40.3
Wheat 4.8 34 26.4 5.3 28 34.5
Other food 65.2 437 34.8 67.7 354 59.2

Notes: Children could have more than one type of food allergy, therefore column percentages do not sum to 100%. The residual percentage of children without each food allergy is omitted. For example, 18% of B cohort children (114 out of 667 children) had a reaction to peanuts, while 72% of children (553 out of 667) had never had a reaction on peanuts; the latter category has been omitted from the table.

Among those with a self-reported food reaction, peanuts were the most common food allergen (18%) in the B cohort, followed by eggs (15%), cow's milk (12%) and other nuts (9%). Soy and sesame were the least commonly reported, at 3% and 2% respectively. A similar pattern was observed in the K cohort, where the four most commonly reported food allergens were peanuts (16%), cow's milk (11%), other nuts (9%) and eggs (9%), while the two least common food allergens were soy (2%) and sesame (< 1%). K cohort sesame food reaction results will not be discussed in subsequent sections due to the low prevalence of this allergy (n = 2); however, the results will be included in the tables.

The mean age of first food reaction, excluding "other food," ranged from 15.1 to 28.6 months in the B cohort and 18.4 to 42.5 months in the K cohort. In the B cohort, the youngest age of mean reactions was to cow's milk (15.1 months) and eggs (15.6 months), while in the K cohort, these figures were for soy (18.4 months) and cow's milk (20.5 months).

Around two-thirds of children in both age cohorts had had a food reaction to "other food" and the mean age of reaction was 34.8 months in the B cohort and 59.2 months in the K cohort. For ease of discussion, results for "other food" will be discussed separately for all subsequent tables.

For all foods, the mean age of first reaction was distinctly younger in the B cohort (6-7 years old) in comparison to the K cohort (10-11 years old). This discrepancy is likely due to recall errors from parents of children in the older cohort rather than reflecting a true difference in age of first reaction.

It is important to note here that children may have more than one food allergy. Sixty children had two food allergies, nine had three food allergies and six had four or more food allergies.

Using this method of diagnosis, more than 90% of IgE-mediated food allergies were found in LSAC to be caused by just nine foods: cow's milk, soy, eggs, wheat, fish, shellfish, peanuts, tree nuts, and sesame. This suggests that the majority of food reactions self-reported in the "other food" category are likely to be non-IgE in nature (i.e., food intolerance or non-IgE mediated), while a lesser proportion are likely to be IgE-mediated in nature (e.g., fish, shellfish and less common IgE-mediated food allergies, such as kiwi fruit).

Parents were asked whether children had had their food reaction tested with a skin prick and/or a food challenge at the hospital, and whether they then tested positive or negative for the food. Table 8.3 describes the prevalence and test results of children in the B cohort at Wave 4 who had undergone allergy testing, by food allergen. Children who had reacted to nuts other than peanuts had most commonly been tested by skin prick (75%), followed by sesame (67%) and peanuts (62%). Children who had reacted to soy, cow's milk or wheat had undergone a skin prick test less than 50% of the time. Overall, skin prick tests were positive in more than 65% of cases. Other nuts and peanuts had the highest rates of positive skin prick tests, with both food types being positive at least 98% of the time.

Table 8.3: Whether food reaction tested and test results, by type of test and food allergen, children who had had a food reaction, B cohort, Wave 4
Allergens Whether tested Test results
Tested (%) Not tested (%) Total (%) No. of observations Positive (%) Negative (%) Total (%) No. of observations
Skin prick test
Peanuts 61.6 38.4 100.0 114 98.0 2.0 100.0 71
Other nuts 74.8 25.2 100.0 61 98.4 1.6 100.0 45
Eggs 56.0 44.0 100.0 97 92.7 7.3 100.0 57
Cow's milk 39.0 61.0 100.0 86 65.8 34.2 100.0 35
Soy 47.3 52.7 100.0 19 82.8 17.2 100.0 10
Sesame 67.0 33.0 100.0 13 88.3 11.7 100.0 9
Wheat 39.2 60.8 100.0 34 68.8 31.2 100.0 13
Other food 16.8 83.2 100.0 437 70.4 29.6 100.0 60
Food challenge test at hospital
Peanuts 12.3 87.7 100.0 114 95.0 5.0 100.0 15
Other nuts 24.6 75.4 100.0 61 100.0 0.0 100.0 13
Eggs 16.5 83.5 100.0 96 92.4 7.6 100.0 18
Cow's milk 12.9 87.1 100.0 87 95.2 4.8 100.0 12
Soy 33.8 66.2 100.0 19 100.0 0.0 100.0 6
Sesame 19.4 80.6 100.0 13 68.5 31.5 100.0 2
Wheat 23.3 76.7 100.0 34 100.0 0.0 100.0 8
Other food 5.2 94.8 100.0 435 79.5 20.5 100.0 22

Notes: Children could have more than one type of food allergy. In some cases, the number of observations for positive or negative test results may not equal the total numbers tested due to item non-response.

A lower proportion of children underwent a food challenge, with fewer than one-third having this test. Soy was the most common food to be tested by food challenge (34%), while other nuts and wheat were food challenged one-quarter of the time. Of those children who reported a food reaction to cow's milk or peanuts, only 12-13% underwent a food challenge. Food challenge outcomes were positive more than 92% of the time for all foods, with the exception of sesame (69%).

Children reporting a food reaction to "other foods" had a lower rate of skin prick test and food challenge compared to any of the seven specific food allergens reported. However, positive allergy test outcomes for "other foods" were within the ranges observed for the specific allergens.

Table 8.4 describes the prevalence and test results of children in the K cohort at Wave 4 who had undergone allergy testing, by food allergen. Children who had reacted to peanuts or other nuts had the highest rates of skin prick tests (69% and 66% respectively), while children who reacted to soy and wheat had the lowest rates of skin prick testing, at less than 30%. Overall, skin prick tests were positive in at least 75% of cases. Wheat (92%), other nuts (92%) and peanuts (91%) had the highest rates of positive skin prick tests.

Table 8.4: Whether food reaction tested and test results, by type of test and food allergen, children who had had a food reaction, K cohort, Wave 4
Allergens Whether tested Test results
Tested (%) Not tested (%) Total (%) No. of observations Positive (%) Negative (%) Total (%) No. of observations
Skin prick test
Peanuts 69.2 30.8 100.0 80 90.7 9.3 100.0 53
Other nuts 66.2 33.8 100.0 42 91.5 8.5 100.0 27
Eggs 45.9 54.1 100.0 47 86.7 13.3 100.0 21
Cow's milk 37.1 62.9 100.0 60 78.2 21.8 100.0 22
Soy 27.3 72.7 100.0 10 75.0 25.0 100.0 4
Sesame 100.0 0.0 100.0 2 100.0 0.0 100.0 2
Wheat 23.8 76.2 100.0 28 92.3 7.7 100.0 5
Other food 14.9 85.1 100.0 352 79.2 20.8 100.0 48
Food challenge test at hospital
Peanuts 22.0 78.0 100.0 78 87.0 13.0 100.0 15
Other nuts 23.6 76.4 100.0 42 100.0 0.0 100.0 10
Eggs 18.1 81.9 100.0 47 71.0 29.0 100.0 8
Cow's milk 14.0 86.0 100.0 60 100.0 0.0 100.0 7
Soy 0.0 100.0 100.0 10 - - - -
Sesame 58.8 41.2 100.0 2 100.0 0.0 100.0 1
Wheat 18.0 82.0 100.0 28 100.0 0.0 100.0 4
Other food 4.4 95.6 100.0 354 84.3 15.7 100.0 14

Notes: Children could have more than one type of food allergy. In some cases, the number of observations for positive or negative test results may not equal the total numbers tested due to item non-response.

Almost one-quarter of the K cohort children had a food challenge test at hospital. Other nuts and peanuts were the most commonly challenged allergens (24% and 22% respectively), while there were no reports of soy being food challenged. Food challenge outcomes were positive more than 70% of the time, and other nuts, wheat and cow's milk tested positive in 100% of cases.

Children reporting a reaction to "other foods" underwent allergy testing less often compared to the seven specific food allergens.

Overall, the rates of skin prick testing for any food allergen were comparable between the B and K cohorts. Peanuts and other nuts were the most commonly tested allergens by skin prick in both age groups, although other nuts were tested more often in the younger cohort (B cohort: 75% vs K cohort: 66%). Skin prick tests were more frequently positive in the K cohort (>= 75%) than the B cohort (> 65%). Peanuts and other nuts had a higher positive test outcome in the B cohort (both 98%) compared with the K cohort (91-92%).

In both age groups, fewer children had a food challenge than a skin prick test. The rate of food challenge tests for food allergens was higher in the B cohort except for other nuts, soy and sesame. Up to one-fifth of the B cohort and 15% of the K cohort had been tested via food challenge (data not shown). Soy was the most commonly challenged food in the B cohort and was not challenged at all in the K cohort. Peanuts were challenged more frequently in the older cohort (22%) and least frequently in the B cohort (12%), while other nuts were food challenge tested at comparable rates.

For each food reaction, parents were asked how long after the child ate the particular food the reaction had appeared. As described in section 8.1, food reactions occurring within one hour of ingestion are likely to be IgE-mediated. Table 8.5 shows that the majority of food reaction symptoms were observed to occur within one hour for both age groups. In the B cohort, the foods with the highest proportion of reactions occurring within half an hour were eggs (89%), other nuts (78%) and peanuts (77%), all of which are typically considered to be IgE-mediated food allergens. Similarly, in the K cohort, the foods with the highest proportion of reactions occurring within half an hour were other nuts (86%) and peanuts (75%).

Table 8.5: Time taken for food reaction, by food allergen, children who had had a food reaction, B and K cohorts, Wave 4
Allergens Less than half an hour (%) Half an hour to an hour (%) 1-4 hours (%) More than 4 hours (%) Total (%) No. of observations
B cohort
Peanuts 77.4 7.5 12.9 2.2 100.0 114
Other nuts 78.2 7.8 6.9 7.1 100.0 61
Eggs 89.4 4.6 3.3 2.7 100.0 97
Cow's milk 43.6 7.5 18.3 30.6 100.0 87
Soy 38.6 0.0 18.1 43.4 100.0 19
Sesame 66.3 0.0 16.5 17.2 100.0 13
Wheat 30.7 5.2 38.3 25.8 100.0 34
Other food 43.1 16.4 21.3 19.2 100.0 437
K cohort
Peanuts 75.0 13.8 6.1 5.1 100.0 81
Other nuts 85.8 4.8 5.6 3.8 100.0 43
Eggs 67.0 10.0 10.8 12.2 100.0 47
Cow's milk 52.6 10.8 12.8 23.7 100.0 61
Soy 68.0 16.8 9.5 5.6 100.0 10
Sesame 100.0 0.0 0.0 0.0 100.0 2
Wheat 29.9 10.4 5.4 54.3 100.0 28
Other food 49.3 16.0 15.5 19.1 100.0 354

Notes: Children could have more than one type of food allergy. Percentages may not total exactly 100.0% due to rounding.

Parents also provided information about the type of reaction children had to each food. As outlined in section 8.1, the type of food reaction symptom can indicate whether the reaction is IgE- or non-IgE mediated. A reaction is thought to be IgE-mediated if a skin rash or vomiting occurs, or if there are signs of anaphylaxis (including breathing difficulties or swelling/tingling of the mouth) within one hour of ingestion. Diarrhoea and stomach ache/pain can occur with either type of reaction. Migraine is a non-specific symptom not usually regarded by specialists as being mediated by food allergy reactions, although migraines in some cases can be triggered in response to adverse reactions to foods.

Table 8.6 shows that for all food allergens in both cohorts, with the exception of wheat in the K cohort, the majority of food reactions resulted in skin rash symptoms.

Table 8.6: Type of food reaction, by food allergen, children who had had a food reaction, B and K cohorts, Wave 4
Allergens Skin rash (%) Vomiting (%) Diarrhoea (%) Stomach ache /abdominal pain (%) Migraine (within 4 hours) (%) Difficulty breathing (%) Swelling/ tingling of mouth (%) Other (%) No. of observations
B cohort
Peanuts 68.2 23.3 3.0 4.6 0.0 18.6 44.7 19.1 114
Other nuts 68.4 20.5 7.0 9.4 0.0 26.4 35.8 10.8 61
Eggs 71.7 20.1 3.3 8.8 0.0 12.0 26.1 16.3 97
Cow's milk 61.6 26.5 21.4 29.5 0.0 5.9 3.8 14.8 87
Soy 53.9 9.4 11.9 23.3 0.0 3.0 0.0 40.5 19
Sesame 59.0 0.0 0.0 19.9 0.0 4.8 19.7 29.3 13
Wheat 56.2 15.8 10.1 40.2 0.0 8.8 3.6 31.9 34
Other food 70.0 6.6 2.7 4.7 0.5 2.8 12.6 23.5 437
K cohort
Peanuts 72.7 8.9 1.9 6.1 1.9 20.6 48.9 17.2 81
Other nuts 62.8 21.8 8.1 16.6 4.3 31.8 47.2 17.5 43
Eggs 77.7 20.3 5.8 6.7 0.0 3.1 19.6 12.0 47
Cow's milk 57.9 26.9 25.1 28.9 0.9 7.8 6.8 11.7 61
Soy 83.6 50.5 22.5 32.1 0.0 0.0 0.0 0.0 10
Sesame 100.0 41.2 0.0 0.0 0.0 0.0 100.0 0.0 2
Wheat 48.0 6.7 21.0 54.0 3.1 5.6 0.0 27.4 28
Other food 63.2 10.5 2.5 5.0 1.7 3.8 16.5 20.2 354

Notes: Children could have more than one type of food allergy and more than one type of reaction.

The most frequent food reaction symptoms reported for eggs were skin rash (B cohort: 72%, K cohort: 78%), swelling or tingling of the mouth (B cohort: 26%, K cohort: 20%) and vomiting (B cohort: 20%, K cohort: 20%). The most frequent food reaction symptoms reported for peanuts were skin rash (B cohort: 68%, K cohort: 73%), swelling or tingling of the mouth (B cohort: 45%, K cohort: 49%) and breathing difficulty (B cohort: 19%, K cohort: 21%). Vomiting was also reported, but more commonly in the younger cohort (23%) than the older cohort (9%). Similarly, for other nuts, the most common food reaction symptoms were: skin rash (B cohort: 68%, K cohort: 63%), swelling or tingling of the mouth (B cohort: 36%, K cohort: 47%) and breathing difficulty (B cohort: 26%, K cohort: 32%).

Breathing difficulty, the most serious form of food reaction, indicates the child is at risk of anaphylaxis. In both cohorts, the two foods that were associated with the highest rates of breathing difficulty were other nuts (B cohort: 26%, K cohort: 32%) and peanuts (B cohort: 19%, K cohort: 21%), while the lowest rates were found with soy (B cohort: 3%, K cohort: 0%).

With the exception of "other food", migraines were only reported in the K cohort and were very rare in younger children.

8.4 Comparisons of groups by probable food allergy or intolerance

Comparison of groups by allergic reactions

The remainder of this chapter compares three groups based on their responses to the questions about allergic reactions. Because data from the gold standard for diagnosis - oral food challenge - were not always available, we collated responses into three groups:

  • probable food allergy - those children who fulfil the criteria for a likely diagnosis of IgE-mediated food allergy for any food reaction through:
  • a positive food challenge; or
  • a reaction within one hour and a positive skin prick test; or
  • a skin reaction, vomiting, diarrhoea, abdominal pain, difficulty breathing or swelling of mouth and a reaction within one hour and a skin prick test or food challenge test, but the result was negative or missing; or
  • a skin reaction, vomiting, diarrhoea, abdominal pain, difficulty breathing or swelling of mouth and a reaction within 1-4 hours and a positive skin prick test;
  • probable food intolerance - those with symptoms consistent with an adverse reaction to a food, but not consistent with an IgE-mediated reaction; and
  • no food allergy/intolerance - those with no history of reaction to a food at all.

It is important to note, however, that the diagnosis of a food allergy or food intolerance among LSAC participants was not always determined by testing through a skin prick or food challenge.

We begin by looking at the risk of probable food allergy in each group by each potential risk factor individually (univariate analysis). The benefit of this type of analysis is that it allows for an examination of patterns of association between food allergies and each individual risk factor. However, univariate analysis does not allow for the effect of multiple risk factors (i.e., it does not consider the potential association between the risk factors themselves), thus such results must be interpreted with caution. At the end of this section, we combine all risk factors into one analysis (multivariate analysis) to assess which factors increase the risk of food allergies, while accounting for the other risk factors.

Table 8.7 shows that the prevalence of probable food allergy and probable food intolerance was higher in the B cohort compared with the K cohort. The rates of probable food allergy were within the 1-11% range of confirmed food allergy reported in children aged 0-16 years (Rona et al., 2007). When comparing the prevalence to age-specific populations (both included in Rona et al.), the rate for the B cohort was higher than that observed in 6-year-old British children (3%) (Venter et al., 2006) and the rate for the K cohort was comparable to that observed in 11-year-old British children (2%) (Pereira et al., 2005).

Table 8.7: Prevalence of probable food allergy or food intolerance, B and K cohort, Wave 4
B cohort K cohort
% n % n
Probable food allergy 4.2 182 2.9 122
Probable food intolerance 11.0 485 9.4 404
No food allergy/intolerance 84.8 3,571 87.7 3,635
Total 100.0 4,238 100.0 4,161

Geographic location and child/family characteristics

Families' postcodes were used to link LSAC and ABS Census data, which identified whether they lived in metropolitan (capital city statistical divisions) or regional areas (the rest of the state outside the capital city statistical divisions). Table 8.8 shows the prevalence of probable food allergy or food intolerance by region. Although the prevalence of probable food allergy seems higher in the metropolitan region for both age groups, the statistical evidence to support this observation is marginal (B cohort: p < .05; K cohort: p = .07).

Table 8.8: Geographic location and prevalence of probable food allergy or food intolerance, B and K cohort, Wave 4
B cohort * K cohort
Metropolitan (%) Regional (%) Metropolitan (%) Regional (%)
Probable food allergy 4.7 3.1 3.3 2.4
Probable food intolerance 11.1 11.0 8.6 10.7
No food allergy/intolerance 84.2 85.9 88.2 86.9
Total 100.0 100.0 100.0 100.0
No. of observations 2,565 1,662 2,500 1,655

Notes: Percentages may not total exactly 100.0% due to rounding. Statistically significant differences are noted: * p < .05.

As documented elsewhere, Vitamin D insufficiency has been linked to an increased risk of food allergy (Sharief et al., 2011). The most accurate method of determining vitamin D status is to measure serum concentrations of 25-hydroxyvitamin D. However, in large population-based studies such as LSAC, this is not always logistically or financially feasible. Since almost all (90-100%) vitamin D requirements can be met by exposure to sunlight - in particular exposure to UVB (Holick, 2003) - it is reasonable to assume that measures of sunlight exposure are an acceptable proxy of vitamin D levels. Living at higher latitudes (i.e., further away from the equator) has been shown to correlate with lower vitamin D levels both in Australia (Daly et al., 2012) and the United States (Looker, Dawson-Hughes, Calvo, Gunter, & Sahyoun, 2002), and has been associated with higher rates of food allergy and asthma (Krstic, 2011; Osborne et al., 2012). The limitation of an approach such as this, is that it describes population characteristics, which may not necessarily translate to the level of risk for an individual. To investigate individual-specific sun exposure, LSAC participants were asked about the frequency of children using sun protection during their time spent outdoors. Although this approach may be subject to recall errors, self-reported sun exposure has shown to be an acceptable measure of sun exposure (Millen & Bodnar, 2008).

Parents were asked how often during the summer months they tried to protect their child from the sun on days when the child was outdoors. Table 8.9 shows a positive trend association between the risk of probable food allergy and increasing frequency of sun protection in the K cohort (p < .01), but not the B cohort. Although these results appear to suggest low vitamin D status plays a role in the development of food allergy, they do not take into account any other factors and thus should be interpreted with caution.

Table 8.9: Frequency of sun protection and prevalence of probable food allergy or food intolerance, B and K cohort, Wave 4
B cohort K cohort **
Every day (%) Most days (%) Some days/ never/ hardly ever (%) Every day (%) Most days (%) Some days/ never/ hardly ever (%)
Probable food allergy 4.3 3.8 5.0 3.3 2.7 1.7
Probable food intolerance 11.1 11.2 9.9 10.2 9.3 4.3
No food allergy/ intolerance 84.7 85.0 85.1 86.6 88.0 94.0
Total 100.0 100.0 100.0 100.0 100.0 100.0
No. of observations 2,930 1,112 195 2,437 1,401 319

Notes: Percentages may not total exactly 100.0% due to rounding. Statistically significant differences are noted: ** p < .01.

To assess geographic latitude, families' state of residence was used as a proxy, resulting in three comparison groups: NT and Queensland (lower latitude); ACT, New South Wales and Western Australia (middle latitude); and South Australia, Tasmania and Victoria (higher latitude). Table 8.10 shows that the risk of probable food allergy, but not probable food intolerance, increases with increasing latitude in both cohorts. However, only in the B cohort did this trend reach statistical significance (p < .05).

Table 8.10: Geographic latitude of family residence and prevalence of probable food allergy or food intolerance, B and K cohort, Wave 4
B cohort * K cohort
NT/Qld (%) ACT/NSW/WA (%) SA/Tas./Vic. (%) NT/Qld (%) ACT/NSW/WA (%) SA/Tas./Vic. (%)
Probable food allergy 1.9 4.6 4.9 1.7 3.0 3.7
Probable food intolerance 11.1 10.6 11.5 9.7 9.0 9.7
No food allergy /intolerance 87.0 84.7 83.6 88.6 88.0 86.6
Total 100.0 100.0 100.0 100.0 100.0 100.0
No. of observations 967 1,819 1,452 933 1,799 1,429

Notes: WA was grouped with ACT and NSW because the vast majority of its population (i.e., Perth/Fremantle) are located at similar latitudes. Percentages may not total exactly 100.0% due to rounding. Statistically significant differences are noted: * p < .05.

Table 8.11 shows that there was no gender difference in the prevalence of probable food allergy or food intolerance in either age cohort. Childhood food allergy is more common in males, yet in adulthood it is more common in females (Sicherer, 2011). The actual timing of this gender switch, however, is uncertain. A similar gender switch occurs around the time of puberty in the prevalence and severity of asthma (Almqvist, Worm, & Leynaert, 2008), and food allergy is hypothesised to also follow this pattern.

Table 8.11: Child gender and prevalence of probable food allergy or food intolerance, B and K cohort, Wave 4
B cohort K cohort
Boys (%) Girls (%) Boys (%) Girls (%)
Probable food allergy 4.2 4.1 2.9 3.0
Probable food intolerance 10.9 11.2 8.5 10.3
No food allergy/intolerance 84.9 84.7 88.6 86.7
Total 100.0 100.0 100.0 100.0
No. of observations 2,184 2,054 2,128 2,033

Table 8.12 shows a trend toward an increasing risk of probable food allergy with increasing family socio-economic position. The highest prevalence rates of probable food allergy were clustered in the group with the highest 25% socio-economic position; however, the gradient was stronger and only significant in the B cohort (p < .01). In contrast, rates of probable food intolerance were comparable across socio-economic groups in both age cohorts. This suggests there may be other factors contributing to the higher rates of food allergy (but not intolerance) in the highest 25% socio-economic group. People from higher socio-economic groups are known to engage in more "health-seeking" behaviours (e.g., going to the doctor) and may therefore be more likely to be diagnosed with a food allergy than those from lower socio-economic groups.

Table 8.12: Family socio-economic position and prevalence of probable food allergy or food intolerance, B and K cohort, Wave 4
B cohort ** K cohort
Lowest 25% SEP (%) Middle 50% SEP (%) Highest 25% SEP (%) Lowest 25% SEP (%) Middle 50% SEP (%) Highest 25% SEP (%)
Probable food allergy 2.3 4.5 6.2 2.4 3.2 3.6
Probable food intolerance 11.1 10.8 11.5 9.1 9.4 9.7
No food allergy/intolerance 86.6 84.7 82.3 88.5 87.4 86.8
Total 100.0 100.0 100.0 100.0 100.0 100.0
No. of observations 1,058 2,119 1,056 996 1,988 995

Notes: Percentages may not total exactly 100.0% due to rounding. Statistically significant differences are noted: ** p < .01.

Children's early life risk factors

Early life risk factors - including breastfeeding, timing of the introduction of solids, birth weight and gestational age - have been hypothesised to play a role in the development of food allergies and other allergic diseases. Information from Waves 1 and 2 of LSAC was used to categorise children based on these early life risk factors.

Based on Waves 1 and 2 data on how long each child had been breastfed, three comparison categories were created: never breastfed, breastfed for less than 6 months, and breastfed for 6 months or longer. Table 8.13 shows a significant positive relationship between duration of breastfeeding and the risk of probable food allergy in the B cohort (p < .05) but not the K cohort.

Table 8.13: Duration of breastfeeding and prevalence of probable food allergy or food intolerance, B and K cohort, Wave 4
B cohort * K cohort
Never breastfed (%) Breastfed < 6 months (%) Breastfed 6+ months (%) Never breastfed (%) Breastfed < 6 months (%) Breastfed 6+ months (%)
Probable food allergy 2.2 3.0 5.0 4.2 2.5 3.0
Probable food intolerance 10.7 9.9 11.2 10.1 9.3 9.3
No food allergy/intolerance 87.1 87.1 83.7 85.6 88.1 87.8
Total 100.0 100.0 100.0 100.0 100.0 100.0
No. of observations 308 1,336 2,134 342 1,337 2,462

Notes: Percentages may not total exactly 100.0% due to rounding. Statistically significant differences are noted: * p < .05.

At Waves 1 and 2, B cohort parents were asked how old their child was when they first had solid food (e.g., baby cereals, puréed fruits, etc.) more than twice a week for several continuous weeks. Table 8.14 shows that the highest prevalence of probable food allergy was in children who had solids introduced at between 4 and 6 months of age, and the lowest was in children who had solids introduced before 4 months. However, as for many of the univariate associations reported here, there was no statistical significance when controlling for other risk factors.

Table 8.14: Timing of the introduction of solids and prevalence of probable food allergy or food intolerance, B cohort, Wave 4
Solids introduced at < 4 months (%) Solids introduced at 4-6 months (%) Solids introduced at 6+ months (%)
Probable food allergy 1.9 4.7 3.8
Probable food intolerance 9.6 11.2 10.4
No food allergy/intolerance 88.5 84.1 85.8
Total 100.0 100.0 100.0
No. of observations 406 3,311 369

Children's birth weight (provided by their parents at Wave 1) was categorised as "normal weight" (2,500 grams and over) or "underweight" (less than 2,500 grams), based on the definition provided by the World Health Organization (2010). Table 8.15 shows the risk of probable food allergy and probable food intolerance is lower in children born at low birth weight compared to those born at normal birth weight in the B cohort (p < .05), but not the K cohort.

Table 8.15: Birth weight and prevalence of probable food allergy or food intolerance, B and K cohort, Wave 4
B cohort * K cohort
Low birth weight (%) Normal birth weight (%) Low birth weight (%) Normal birth weight (%)
Probable food allergy 2.7 4.3 2.0 3.1
Probable food intolerance 7.1 11.3 8.7 9.3
No food allergy/intolerance 90.2 84.4 89.3 87.6
Total 100.0 100.0 100.0 100.0
No. of observations 219 3,996 260 3,847

Notes: Statistically significant differences are noted: * p < .05.

Children's gestational age (provided by their parents at Wave 1) was categorised as "pre-term" (born at 36 weeks or earlier) or "normal" (born at 37 weeks or later, including late births) (Laws & Sullivan, 2009). Table 8.16 shows that the risk of probable food allergy in B cohort children born at 36 weeks or earlier was significantly lower than those born at term or later (p < .01), but in the K cohort was comparable between gestational age categories.

Table 8.16: Gestational age and prevalence of probable food allergy or food intolerance, B and K cohort, Wave 4
B cohort ** K cohort
Pre-term (%) Normal (%) Pre-term (%) Normal (%)
Probable food allergy 3.4 4.2 2.2 3.0
Probable food intolerance 5.5 11.5 7.8 9.4
No food allergy/intolerance 91.1 84.3 90.0 87.6
Total 100.0 100.0 100.0 100.0
No. of observations 269 3,963 302 3,832

Notes: Statistically significant differences are noted: ** p < .01.

Significant associations between food allergy and early life characteristics were more common in the B cohort compared with the K cohort. The rates of probable food allergy were lower in LSAC children with a low birth weight and those born pre-term in the B cohort (but not the K cohort). However, previous research has shown low birth weight/prematurity not to be associated with food allergy (Pali-Scholl et al., 2009) but with wheezing (Kumar et al., 2008), and to be protective against sensitisation to inhalant allergens (aeroallergens) such as birch pollen and cat fur (Siltanen et al., 2011) and to atopic dermatitis (Buhrer, Grimmer, Niggermann, & Obladen, 1999).

Asthma and eczema

At each wave, children's parents were asked whether they had ever had a doctor tell them that their child had asthma, and their reports from this question at Wave 4 are used here. Table 8.17 shows that the risk of probable food allergy is more than double in children with co-existent asthma compared to children without asthma in both age cohorts (p < .01).

Table 8.17: Whether child has asthma and prevalence of probable food allergy or food intolerance, B and K cohort, Wave 4
B cohort ** K cohort **
Asthma (%) No asthma (%) Asthma (%) No asthma (%)
Probable food allergy 7.9 2.9 5.5 1.6
Probable food intolerance 14.4 9.7 11.4 8.1
No food allergy/intolerance 77.7 87.4 83.1 90.2
Total 100.0 100.0 100.0 100.0
No. of observations 1,072 3,135 1,379 2,774

Notes: Percentages may not total exactly 100.0% due to rounding. Statistically significant differences are noted: ** p < .01.

At each wave, parents reported on whether their child had eczema (not necessarily diagnosed by a doctor), and information from Wave 4 is used here. Table 8.18 shows the risk of probable food allergy is four-fold higher in children with co-existent eczema in both cohorts (p < .01).

Table 8.18: Whether child has eczema and prevalence of probable food allergy or food intolerance, B and K cohort, Wave 4
B cohort ** K cohort **
Eczema (%) No eczema (%) Eczema (%) No eczema (%)
Probable food allergy 13.3 2.8 12.2 1.8
Probable food intolerance 22.3 9.3 14.3 8.8
No food allergy/intolerance 64.5 87.9 73.5 89.4
Total 100.0 100.0 100.0 100.0
No. of observations 556 3,682 453 3,708

Notes: Percentages may not total exactly 100.0% due to rounding. Statistically significant differences are noted: ** p < .01.

Multivariate analysis of demographic and risk factors

Demographic, early life characteristics and other antecedent (risk) factors were combined into one analysis (logistic regression analysis) to assess the effects of each factor on the risk of probable food allergy, while controlling for the influence of all other factors examined in this chapter.3 Results in this type of analysis are expressed as an odds ratio (OR), which indicates the likelihood of a child being food allergic if they have the risk factor compared to if they don't have the risk factor. An OR greater than 1 indicates a positive association, while an OR less than 1 indicates a negative one.

The results from the combined models showed that children in the B cohort were more likely to be food allergic if they had co-existent eczema (OR = 5.08, p < .001), or co-existent asthma (OR = 2.86, p < .001). In other words, B cohort children with eczema had more than five times the odds of being food allergic than children without eczema, and children with asthma had nearly three times the odds of being food allergic than children without asthma.

Similarly, children in the K cohort were more likely to be food allergic if they had co-existent eczema (OR = 7.41, p < .001), co-existent asthma (OR = 3.36, p < .001), or if they had never been breastfed (OR = 2.00, p < .05). K cohort children were less likely to be food allergic if they lived in lower latitude regions (i.e., NT and Queensland) (OR = 0.48, p < .05).

Many of the associations observed in the univariate analyses were not significant when combined into a logistic regression model, indicating the initial results were distorted by the relationships among the risk factors. Similarly, associations that were not significant in the univariate analyses - specifically breastfeeding and latitude in the K cohort - were significant in the multivariate model. Again, this is likely related to the interplay between risk factors.

Of note here is the apparent contradiction in findings for breastfeeding. In the initial analyses, a relationship between food allergy and a longer duration of breastfeeding was found in the B cohort, but not the K cohort. Yet in the regression analysis for the K cohort, those who had never been breastfed were more likely to have a food allergy. The discrepancy seen in the first analysis between the age groups may simply be a reflection of the ambiguous relationship between breastfeeding and food allergies described by Matheson et al., (2012). Alternatively, it may be a result of "reverse causation", whereby infants perceived to be at high risk of food allergy are breastfed for a longer duration (in response to changing infant feeding guidelines, for example) than those perceived to be at low risk, creating an apparent positive association between breastfeeding and food allergies.

8.5 Summary and discussion

This chapter has provided a snapshot of the prevalence of and factors associated with childhood food allergies in Australia, using Wave 4 LSAC data from the B cohort (6-7 year olds) and K cohort (10-11 year olds). It describes the prevalence of food reactions and "probable" food allergy, and the types of food causing and presenting features of food allergy reactions, and investigates the relationship between various demographic and antecedent factors and food allergy risk.

Overall, 15% of 6-7 year olds and 12% of 10-11 year olds had ever had a reaction to food. As would be expected, when classified using clinical criteria, a significantly lower number of children were considered to have had a "probable food allergy" (B cohort: 4%, K cohort: 3%). Consistent with previous reports by others, the prevalence of food reactions and food allergies was higher in younger children (Rona et al., 2007).

The four most common types of food reported to cause a reaction were peanuts, eggs, cow's milk and other nuts, while soy and sesame had the lowest reaction rates. Eggs, cow's milk and soy were reported to cause reactions earlier in life than foods that are typically introduced to the diet later (e.g., other nuts and sesame).

"Other food" accounted for around two-thirds of food reactions and was associated with a later age of first reaction. As discussed, this group is likely to predominantly involve food intolerances and non-IgE-mediated reactions.

Overall, the rates of skin prick tests were comparable between younger and older children, and in both age groups, peanuts and other nuts were the foods most commonly tested by skin prick. Food challenges were administered more frequently in younger children (one-fifth) compared with older children (15%). Younger children were challenged to soy most often and least often to peanuts. In contrast, older children were more often challenged to peanuts and least to soy. We expected a higher rate of children in the older age group undergoing food challenge tests for peanuts, as doctors seek to determine the development of tolerance with age.

Food allergies can be classified as being IgE- or non-IgE mediated, based on the symptoms and timing of onset of symptoms in addition to the type of food allergen. The results were consistent with the notion that peanuts, tree nuts and eggs cause IgE-mediated food allergies (i.e., within one hour, skin rash symptoms and signs of anaphylaxis show), and that wheat is non-IgE mediated (i.e., symptoms show after 4 hours and are likely to be non-specific).

Risk factors for food allergies were investigated. Initial results suggested the prevalence of food allergies increased for children who lived in urban areas (for the B cohort), and had co-existent asthma or eczema (for both cohorts).

These results, however, were a preliminary analysis and did not account for other potential confounding factors, such as gender, socio-economic position and other risk factors investigated within this report. When all demographic and antecedent risk factors were considered together, the only two that increased the risk of food allergies consistently across age groups were co-existent eczema and asthma. The strongest association with food allergy was co-existent eczema; in both younger and older children, those with eczema had up to seven times the odds of being food allergic than children without eczema. Additional lifestyle risk factors in older children were not having been breastfed and living in southern areas of Australia.

The limitations of the results presented in this chapter include the self-report nature of the data and that questions were focused on lifetime food reaction history. The rate of self-reported food allergy is known to be higher than that of diagnosed food allergy (Venter et al., 2006, 2008), and self-reported data can be affected by inaccurate recall. We created an objective classification of food allergies, based on descriptions of clinical symptoms, and found a rate of probable food allergy comparable to existing research. In addition, parents were asked questions about lifetime, as opposed to current and past, food reactions. Since many children with an early food allergy develop tolerance before the age of five (Wood, 2003), it is possible that a subset had already outgrown their food allergy by the time of the questionnaire administration.

Nevertheless, these findings suggest a high prevalence of food allergy among Australian children aged 6-11 years, with the majority of affected children having received some form of allergy testing. Food allergy questions were first asked in Wave 4 of the LSAC study. Analysis of future waves of LSAC data will allow for a longitudinal investigation of childhood food allergies and enable researchers to explore factors contributing to the persistence of food allergies and the development of tolerance.

8.6 References

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Asher, M., Barry, D., Clayton, T., Crane, J., D'Souza, W., Ellwood. P. et al. (2001). The burden of symptoms of asthma, allergic rhinoconjunctivitis and atopic eczema in children and adolescents in six New Zealand centres: ISAAC Phase One. New Zealand Medical Journal, 114(1128), 114-120.

Asher, M., Montefort, S., Bjorksten, B., Lai, C. K., Strachan, D. P., Weiland, S. K., & Williams, H. (2006). Worldwide time trends in the prevalence of symptoms of asthma, allergic rhinoconjunctivitis, and eczema in childhood: ISAAC Phases One and Three repeat multicountry cross-sectional surveys. The Lancet, 368(9537), 733-743.

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Footnotes

1 A food challenge is a test during which a suspect food is fed to the child and any reactions observed.

2 In the Longitudinal Study of Australian Children (LSAC) questionnaire, parents were asked whether their child had ever had a reaction (such as redness or itching) that they thought was due to food that the child had eaten. As this question did not differentiate between allergic and intolerance reactions, responses are likely to also include intolerance reactions (e.g., lactose or gluten intolerance).

3 The factors included in the regression models were: child gender, geographic location (metropolitan/regional), frequency of sun protection (every day, most days, some days/never/hardly ever), geographic latitude (NT/Qld, ACT/NSW/WA, SA/Tas./Vic.), family socio-economic position (lowest 25%, middle 50%, highest 25%), duration of breastfeeding (never, less than 6 months, 6 months or longer), timing of the introduction of solids (B cohort only; before 4 months of age, 4-6 months, 6 months or later), birth weight (low, normal), gestational age (36 weeks or earlier, 37 weeks or later), asthma, and eczema.

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