Table 1.

Importance of peanut and different tree nuts as allergen sources in different parts of the world.

Region	Test methodology	Subjects tested	Allergens tested	Results	References
Europe (11 countries), USA, Australia	Sera were screened for specific IgE to food allergen mixes and individual foods using ImmunoCAP. Test was considered positive if sIgE ≥ 0.35 kUA/L.	4522 young adults (aged 20–44) were tested for at least one allergen mix. 4220 were tested for all five food allergen mixes. Participants had been previously included in the “random sample” group during the second phase of the European Community Respiratory Health Survey.	Walnut Peanut Hazelnut (no information on individual allergen molecules)	Sensitization by country (%): Walnut: Germany (3.3), Italy (3.1), France (3.7), Belgium (2.5), USA (2.1), Australia (2.1), Spain (3.1), Norway (0.6), Sweden (1.1), UK (0.8), Iceland (0.0), Overall (2.2, excluding birch positive 1.8) Peanut: Germany (4.2), Italy (3.6), France (3.0), Belgium (2.0), USA (9.3), Australia (3.0), Spain (1.9), Norway (0.8), Sweden (1.0), UK (1.5), Iceland (1.2), Overall (2.6, excluding birch positive 1.8) Hazelnut: Germany (14.7), Italy (7.7), France (5.0), Belgium (6.0), USA (14.9), Australia (4.1), Spain (2.6), Norway (12.8), Sweden (11.8), UK (4.9), Iceland (0.4), Overall (7.2, excluding birch positive 3.1)	(48)
Europe (8 centers: Zurich, Madrid, Utrecht, Lodz, Sophia, Athens, Reykjavik and Vilnius)	Questionnaire followed by serum analysis. Detection of IgE sensitization to groups of food allergens and individual foods using ImmunoCAP, which was considered positive if sIgE ≥ 0.35 kUA/L. Sera of subjects were tested for IgE reactivity to specific food allergens using an allergen microarray assay.	Serum samples taken from in total 719 potentially-food allergic adults (aged 20-54) and 1642 controls. Up to 240 potentially food-allergic subjects per center and 240 controls, oversampling of centers with less than 240 cases (applied for all centers).	Hazelnut Walnut Peanut (individual allergen molecules tested)	IgE sensitization to food allergy by center (first number: percentage of weighted IgE-sensitization prevalence; second number: percentage of weighted IgE-sensitization prevalence to “true” food allergens not associated with cross-reactivity to plant pollen allergens): Hazelnut : Zurich (17.8, 1.1), Madrid (6.0, 2.4), Utrecht (12.0, 0.0), Lodz (6.5, 0.3), Sofia (6.3, 3.0), Reykjavik (1.3, 0.7), Overall (9.3, 0.9) Walnut: Zurich (5.6, 0.1), Madrid (7.7, 0.4), Utrecht (1.9, 0.1), Lodz (3.6, 0.3), Sofia (2.7, 0.0), Reykjavik (0.1, 0.0), Overall (3.0, 0.1) Peanut: Zurich (5.0, 0.4), Madrid (7.2, 0.5), Utrecht (1.6, 0.1), Lodz (3.1, 0.0), Sofia (1.8, 0.0), Reykjavik (0.5, 0.1), Overall (2.7, 0.14)	(50)
UK (Isle of Wight)	Clinical peanut allergy and/or IgE sensitization of participants was determined. Sensitization to peanuts determined by a wheal size ≥ 3 mm in presence of negative control during SPT. Clinical allergy was confirmed by positive SPT and convincing history or positive OFC (only Cohorts B and C).	Peanut allergy prevalence was assessed in three cohorts of children born on the Isle of Wight. Cohort A: 2181 children (aged 4) born in 1989 Cohort B: 1273 children (aged 3-4) born between 1994-1996 Cohort C: 891 children (aged 3) born between 2001-2002 Number of patients included for evaluating clinical allergy: Cohort A: 1218 Cohort B: 1273 Cohort C: 891 Number of patients tested by SPT: Cohort A: 981 Cohort B: 1246 Cohort C: 642	Peanut (commercial extracts)	Percentage of sensitization: Cohort A: 1.3 Cohort B: 3.3 Cohort C: 2.0 Percentage of clinical peanut allergy diagnosis based on positive SPT and clinical history or positive OFC: Cohort A: 0.5 Cohort B: 1.4 Cohort C: 1.2	(53)
UK	Families were chosen by primary questionnaire. Mothers were asked about their peanut allergy status and dietary changes regarding peanut consumption during pregnancy. Selected children underwent SPT. SPT was considered positive if wheal size ≥ 3 mm in presence of negative control and wheal size of at least 3 mm to histamine (1:10w/v). Sera from children with positive SPT were tested for peanut-specific IgE using ImmunoCAP. Those showing IgE sensitization underwent OFC.	1072 mother-child pairs (children aged 3-6 years) were chosen for allergy testing based on valid questionnaire.	Peanut (allergen extracts for SPT, peanut flour-based biscuits for OFC)	30 of 1072 children (2.8%) showed IgE sensitization to peanut, confirmed by positive SPT or high peanut-specific IgE levels (> 100 kUA/L). 21 children underwent DBPCFC of which 15 had positive results. 5 children had convincing medical history and supportive blood and skin test results. 20 of 1072 children (1.8%) were considered to have clinical peanut allergy.	(54)
UK	Participants were recruited prenatally. At the age of 8 years information on exposure and reactivity to peanut was collected by a questionnaire. Peanut sensitization was confirmed by SPT with wheal size of at least 3 mm greater than the negative control and/measurement of IgE (≥ 0.2 kUA/l) using ImmunoCAP. Sensitized patients underwent OFC. Three children underwent open OFC with roasted peanuts. Peanut-consuming children underwent open OFC with peanut protein in brownies. All others underwent DBPCFCs with peanut protein-containing brownies. The sensitization profile of peanut-allergic children was compared to the profile of those who were considered tolerant using microarray assays.	933 children at age 8 years (unselected population-based birth cohort)	Peanut (tested for individual allergen molecules; peanut protein in brownies for OFC and DBPCFC; three children with milk/egg allergy underwent open OFC with roasted peanuts)	110 of 933 children (11.8%) were considered sensitized to peanut. 19 were not further challenged. 12 children were considered peanut-allergic due to reports of allergic reactions together with sIgE ≥ 15 kUA/L and/or SPT ≥ 8 mm without further challenge. Of the remaining 79 subjects that underwent OFC, 7 were considered allergic due to showing objective symptoms. Ara h 2 was the most relevant predictor of clinical peanut allergy.	(55)
UK	Evaluation of ethnic differences in nut sensitization profiles. Sensitization was assessed by SPT. Wheal size ≥ 3 mm was considered sensitization and ≥ 8 mm was defined as allergy.	Data from 2638 patients was collected (new referrals at the children’s allergy clinic in Leicester).	Almond Hazelnut Peanut Pecan Brazil nut Cashew Pistachio Walnut (allergen solutions and whole nuts for SPT)	Nut sensitization (SPT wheal ≥ 3 mm) and allergy (SPT wheal ≥ 8 mm) in south Asian children (percentage of all tested): Almond: 61.9, 7.4 Brazil nut: 17.2, 1.5 Cashew: 69.1, 27.4 Hazelnut: 30.5, 4.2 Peanut: 63.2, 30.3 Pistachio: 64.3, 25.7 Pecan: 26.9, 8.3 Walnut: 30.1, 8.1 Nut sensitization (SPT wheal ≥ 3 mm) and allergy (SPT wheal ≥ 8 mm) in White children (percentage of all tested): Almond: 31.1, 1.8 Brazil nut: 20.1, 5.4 Cashew: 35.6, 10.6 Hazelnut: 25.8, 2.4 Peanut: 64.7, 36.1 Pistachio: 31.2, 6.9 Pecan: 24.7, 7.1 Walnut: 20.8, 5.4	(56)
UK Israel	Participants completed validated questionnaires about food allergy (schoolchildren) or food consumption (infants) (period 2004-2005). Food frequency questionnaire was completed by the mothers of the infants. Food allergy questionnaires in primary schools were completed by the children’s parents. Children with questionnaire-based peanut allergy were invited for allergy testing (SPT, sIgE or both) which was considered positive if results were > 95% positive predictive values or in case of positive OFC.	The food allergy questionnaire was returned by 4148 Jewish schoolchildren (aged 4-19 years) in the UK and 4672 in Israel. Food frequency questionnaire included 77 Jewish infants (aged 4-24 months) in the UK and 99 in Israel.	Peanut Tree nuts (questionnaire based; products for allergy testing not further specified)	Questionnaire-based peanut allergy prevalence was 1.85% in the UK and 0.17% in Israel. Of peanut-allergic children, 58.9% (43 of 73) in the UK and 50% (4 of 8) in Israel had tree nut allergy. Dietary introduction of peanut occurred earlier in Israel than the UK. At age 9 months, 69% of infants in Israel and 10% in the UK were eating peanuts.	(57)
Denmark	Questionnaire followed by SPT, histamine release (HR) assay and OFC. Positive SPT was defined as wheal size ≥ 3 mm. Histamine release of ≥ 10 ng/ml was considered as positive. DBPCFC was performed for peanut using peanut-containing chocolate bars. Distinction made between primary food hypersensitivity (FHS) (independent of pollen) and secondary FHS (pollen allergic patients).	Total study population were 1272 unselected young adults (age 22 years), of which 843 responded to questionnaire and were included in the analysis.	Peanut Almond Hazelnut Brazil nut Walnut (only peanut was used for SPT (fresh peanut) and OFC (peanut in chocolate bars))	223 of 843 subjects that returned the questionnaire suspected FHS. Of those, 165 self-reported primary FHS (independent of pollen) and 141 secondary FHS (pollen-associated). Prevalence of primary FHS: Peanut: Self-reported n (%): 45 (5.3) Challenged n: 12 Confirmed by OFC n (%): 5 (0.6) Prevalence of secondary FHS (only self-reported): Almond n (%): 2 (0.2) Brazil nut n (%): 23 (2.7) Hazelnut n (%): 56 (6.6) Walnut n (%): 4 (0.5)	(58)
France	Clinical symptoms of asthma, allergic rhinitis and food allergy assessed using a questionnaire that was completed by the parents. Evaluation of food allergy prevalence and its association with respiratory manifestations of allergy by SPT to food and aeroallergens. For positive SPT wheal size had to be ≥ 3 mm and greater than the negative control.	In total, 6672 schoolchildren (aged 9-11 years) from 108 randomly chosen schools were recruited for clinical examination and completed the questionnaire.	Peanut Tree nuts, only listed as “nuts” and not further defined (only peanut was tested by SPT)	Reported symptoms of FA, n (%): Peanut: 21 (0.3) Nuts: 10 (0.2) Food sensitization n (%): Peanuts: 70 (1.1) Of the children sensitized to at least one food allergen (n = 119), 58.8% were sensitized to peanut. About 26.7% were sensitized to at least one aeroallergen. Of the 10 children that reported symptoms to nuts, 22.2% were sensitized to birch pollen.	(59)
Finland	Investigation of nut sensitization and cross- and co-sensitization to other nuts and birch pollen by using available SPT data. SPT was considered positive if wheal size was at least 3 mm.	50604 patients (children and adults) at the Helsinki Allergy Hospital (1997–2013), that underwent SPT to at least one nut (18603 birch-positive, 32001 birch-negative).	Peanut Hazelnut Almond Pistachio Macadamia Walnut Cashew Pecan Brazil nut (for SPT raw nuts were used (prick-to-prick method))	Of 50604 patients that were tested for nuts, 36.8% were birch positive and 63.2% were birch-negative. Nut sensitization in birch-positive patients (%): Hazelnut: 84 Almond: 71 Peanut: 60 Pistachio: 55 Macadamia: 45 Walnut: 41 Cashew: 28 Pecan: 21 Brazil nut: 18 Nut sensitization in birch-negative patients (%): Pistachio: 14 Cashew: 12 Walnut: 11 Macadamia: 10 Brazil nut: 8 Pecan: 8 Peanut: 7 Almond: 6 Hazelnut: 5 In a subgroup of patients without birch sensitization, children <5 years were most commonly nut‐sensitized (8–40%), with decreasing prevalence with age. Cross-reactivity was strongest between cashew and pistachio and pecan and walnut.	(60)
Turkey	Initial selection based on 6963 available questionnaires of subjects with suspected food allergy, followed by a telephone interview. Clinical diagnosis of consented patients by SPT, physical examination, sIgE and OFC. SPT was considered positive if wheal size was at least 3 mm in comparison to the negative control. SIgE was measured by ImmunoCAP.	Study included 6963 schoolchildren (aged 10-11 years) from the multicenter ISAAC Phase II study (2005-2006). 1162 children, including 909 symptom-positive, 301 SPT-positive and 48 for which applied both were selected and 813 participated in a telephone interview. Of 152 adolescents with current complaints, 87 agreed to clinical investigation.	Peanut Hazelnut Walnut Pistachio (commercial extracts or prick-to-prick testing)	Percentage of parental-reported food allergy prevalence in the ISAAC Phase II study population (n = 6963): Pistachio: 0.8 Walnut: 1.2 Peanut: 1.4 Hazelnut: 1.5 Percentage of SPT-confirmed prevalence in the ISAAC Phase II study population: Hazelnut: 0.4 Peanut: 0.7 Walnut: 4.5 In total, 12 food allergies were diagnosed in 9 adolescents including allergy to peanut (n = 1), hazelnut (n = 1) and walnut (n = 3).	(61)
Turkey	Pre-selection by questionnaire, clinical evaluation by SPT and DBPCFC. SPT was considered positive if wheal size diameter was at least 3 mm in presence of a negative control and a positive histamine reaction after 15 minutes. DBPCFC was preceded by a 7-day elimination diet.	2739 of 3500 randomly selected schoolchildren (aged 6-9 years) from the eastern Black sea region of Turkey returned questionnaire. SPT was performed in 145 children and DBPCFC was performed in 44 children.	Hazelnut Walnut Peanut (commercially available extracts for SPT; DBPCFC performed with all three nuts, masked in chocolate pudding)	Of the 2739 subjects that returned the questionnaire, 156 had parent-reported IgE-mediated food allergy and were further recruited for a second-phase study. Of these 156 children, 145 underwent SPT of which 48 were considered positive to at least one food. 41 children with positive SPT and 3 with negative SPT underwent DBPCFC. Nuts that were most commonly associated with allergic reactions (of total foods reported (n = 256), food positive in SPT (n = 88) and positive in OFC (n = 22)): Hazelnut: Reported n (%): 8 (3.1) SPT n (%): 2 (2.2) DBPCFC n (%): 0 (0) Peanut: Reported n (%): 3 (1.1) SPT n (%): 2 (2.2) DBPCFC n (%): 0 (0) Walnut: Reported n (%): 3 (1.1) SPT n (%): 2 (2.2) DBPCFC n (%): 0 (0)	(62)
Turkey	Pre-selection of adolescents by parental questionnaire and phone survey. Clinical evaluation in selected patients by SPT (positive if wheal diameter at least 3 mm), measurement of specific IgE by ImmunoCAP (> 0.35 kUA/L for positive result) and DBPCFC.	10,096 parents of schoolchildren (aged 11-15 years) responded to a questionnaire. Of those, 1139 reported food allergy of their children and were selected for phone survey. Finally, 107 adolescents were selected for clinical evaluation.	Peanut Walnut Hazelnut Almond Pistachio (commercially available extracts for SPT; hazelnut peanut and walnut were masked in chocolate pudding for DBPCFC)	Clinical evaluation (n = 107) of pre-selected patients with suspected food allergy: Walnut (n = 14): SPT positive: 4/14 sIgE positive: 3/14 DBPCFC: 4/5 Hazelnut (n = 11): SPT positive: 1/11 sIgE positive: 1/11 DBPCFC: 1/3 Peanut (n = 9): SPT positive: 6/9 sIgE positive: 3/9 DBPCFC: 4/6 Almond (n =1): SPT positive: 0/1 sIgE positive: 0/1 No DBPCFC Pistachio (n =1): SPT positive: 1/1 sIgE positive: 1/1 No food challenge due to history of anaphylaxis The most common foods causing allergies were peanut (0.05%) and tree nuts (0.05%).	(63)
Russia	Initially, parents completed the international ISAAC questionnaire. Based on the questionnaire two groups of children were formed (with and without symptoms of allergy). All children underwent SPT and sera from both groups were tested for sIgE using microarray-based allergen chip (MeDALL allergen chip). Allergen-specific IgE level of = or > 0.3 ISU was considered positive.	In total, 200 children that attended the National Research Center—Institute of Immunology Federal Medical‐Biological Agency of Russia with their parents were included in this study. Group 1: Children with allergic symptoms (n = 103; 12.24 ± 2.23 years) Group 2: Children without allergic symptoms (Group 2: n = 97; 12.78 ± 2.23 years)	Hazelnut Peanut Walnut Cashew Pistachio Brazil nut (tested for individual allergen molecules)	Food allergen-specific IgE sensitization was dominated by cross-reactive allergens (PR10 proteins) such as rAra h 8 (peanut) rCor a 1 (hazelnut), with the latter being among the most frequently recognized allergens (52.4%) in symptomatic children. Within the group of symptomatic children (n = 103) the following nut allergens were recognized, n (%): rCor a 1 (hazelnut): 54 (52.4) rAra h 8 (peanut): 47 (45.6) nJug r 2 (walnut): 15 (14.5) rJug r 3 (walnut): 8 (7.8) rAra h 9 (peanut): 6 (5.8) rCor a 8 (hazelnut): 5 (4.8) nAna o 2 (cashew): 2 (1.9) nCor a 9 (hazelnut): 2 (1.9) rJug r 1 (walnut): 2 (1.9) rAna o 3 (cashew): 1 (0.9) rAna o 1 (cashew): 1 (0.9) nAra h 1 (peanut): 1 (0.9) rPis v 3 (pistachio): 1 (0.9) rCor a 14 (hazelnut): 0 rBer e 1 (Brazil nut): 0 rPru du 3 (Almond): 0 rPru du 4 (Almond): 0 rPru du 6 (Almond): 0 rPru du 6.01 (Almond): 0 rPru du 6.02 (Almond): 0 nAra h 3 (Peanut): 0 nAra h 6 (Peanut): 0 rAra h 2 (Peanut): 0 Similarly, recognition of PR10 proteins predominated in subjects without symptoms. Of genuine nut allergens not associated with respiratory sensitization, walnut allergens were most commonly recognized in the symptomatic group. The lack of reactivity to peanut storage proteins suggests low prevalence of peanut allergy in Russia.	(38)
Iran	Initial questionnaire in 2 different groups: population within the Kerman Province, the largest pistachio cultivation region of the world, and a population outside this region. Adults completed the questionnaire themselves or as guardians for their children. Clinical evaluation by SPT and testing of in vitro cross-reactivity with other nuts by Western blot and inhibition ELISA. SPT was considered positive with a wheal diameter > 3 mm in regard to the negative control.	1724 subjects responded to the questionnaire. Within the pistachio cultivation region were 564 responses (average age 31.35 ± 13.6 years). In the population outside this region were 1160 responses received (average age 37 ± 10 years). Clinical evaluation of 21 patients. Testing of IgE-cross-reactivity in 3 pistachio-allergic patients.	Pistachio (protein extracts used for SPT) Cashew Almond Peanut (protein extracts used for cross-reactivity study)	Questionnaires revealed a pistachio allergy prevalence of 0.65% within the pistachio cultivation site and a prevalence of 0.3% for outside this region based on reports of allergic reactions to pistachios. Cross-reactivity between pistachio and cashew was shown, followed by partial cross-reactivity between pistachio and almond (determined by inhibition ELISA).	(64)
Iran	Medical record review of patients referred to the Immunology and Allergy Medical Center of Khatam Hospital during a 7-year period (1996-2003). Patients underwent SPT and responded to a questionnaire. SPT with wheal diameter > 3 mm in regard to the negative control and flare diameter of > 10 mm were considered positive.	1286 allergic patients (aged 2-79 years) were included.	Walnut Hazelnut (no information on individual allergen molecules)	29.16% of patients were sensitized to walnut and 15.32% were sensitized to hazelnut, determined by positive SPT.	(65)
South Korea	Retrospective medical record review performed in 14 university hospitals in South Korea (2009–2013) in order to collect cases of anaphylaxis that were caused by peanut, tree nuts or seeds. Measurement of sIgE levels using ImmunoCAP and SPT. SPT was considered positive if wheal diameter > 3 mm or ≥ the histamine control.	Pediatricians identified 991 cases of anaphylaxis in patients (< 19 years) based on retrospective medial record review. IgE data of 104 patients available, 11 patients underwent SPT.	Peanut Walnut Almond Hazelnut Cashew Pistachio Pecan Macadamia (products used for testing not specified)	In total, 126 of 991 cases of anaphylaxis were caused by peanut, tree nuts or seeds. Affected patients were between 0.8 and 18.9 years old (over 80% of children < 7 years old). Nuts that caused anaphylaxis, n (%): Peanut: 41 (32.5) Walnut: 52 (41.3) Cashew: 6 (4.8) Almond: 3 (2.4) Hazelnut: 3 (2.4) Pecan: 3 (2.4) Pistachio: 1 (0.8) Macadamia: 1 (0.8) In 104 cases, sIgE levels were measured. Median sIgE levels to peanut and walnut were 10.50 and 8.74 kUA/L.	(66)
China	Medical records of patients at the First Affiliated Hospital of Zhengzhou University, Henan Province, China (2012-2016) were retrospectively analyzed. SIgE of Patients was measured by AllergyScreen test with sIgE ≥ 0.35 IU/mL being considered positive.	Medical records of 15534 patients with suspected allergy were included. The study population included 7388 males and 8146 females (5257 children and 10277 adults). The average age was 30.56 ± 20.98 years.	Cashew (no information on individual allergen molecules)	Cashew nut was one of the most frequent tested food allergens (n = 1320, 8.5%).	(67)
China	Parents that attended routine baby health checks with their children at the Department of Primary Child Care, Children’s Hospital of Chongqing Medical University were asked to complete a questionnaire. Children underwent SPT. Wheal size of ≥ 3 mm greater than the negative control was considered positive. Children with positive SPT or positive medical history were asked to undergo OFC (not for peanut).	497 infants and young children (aged 0-12 months) were included in the study, of which 477 fully participated.	Peanut (product used not further specified)	In 46 of 497 cases parents reported allergic reactions of their children to food. 2 subjects had positive SPT to peanut.	(68)
China	Two cross‐sectional studies were performed, the first in 1999 and the second in 2009. Children that attended the division of Primary Child Care, Children’s Hospital, Chongqing Medical University for well-baby checking were randomly enrolled. Parents completed an initial questionnaire. Subsequently, all subjects underwent SPT. SPT was considered positive if wheal diameter was at least 3 mm larger than the negative control. Elimination diet was followed by OFC if positive effect of food elimination was observed.	In total, 401 infants were randomly selected (0-24 months), and 382 were included in the final analysis (in study from 2009). Results were compared with study from 1999. In 1999, 314 questionnaires were returned and infants were skin prick tested. 10 infants dropped out during food elimination, thus, 304 were included in the final analysis.	Peanut (Extracts or prick-to-prick technique used for SPT; peanut butter used for oral provocation)	Of 32 infants with positive SPT in 1999, 1 showed reactivity to peanut. In 2009, 72 infants had positive SPT, including 6 that reacted to peanut. In 1999, peanut was among the offending foods causing food allergy in infants (observed in 1 of 11 children with challenge-confirmed food allergy). In 2009, confirmed food allergy only included egg and cow´s milk.	(69)
Singapore	Retrospective study to evaluate clinical features of peanut allergy in children in the largest pediatric hospital in Singapore. Peanut allergy was diagnosed based on medical history, together with SPT (positive of wheal diameter of ≥ 3 mm in comparison to the negative control), sIgE (positive for sIgE ≥ 0.35 kUA/L) and OFC.	269 children (≤ 16 years old) with clinical diagnosis of peanut allergy were included.	Peanut Cashew Almond Hazelnut Walnut (SPT with commercial extracts; OFC using peanut butter or roasted peanuts)	269 patients that were diagnosed with peanut allergy were identified, together with 59 patients that were considered peanut tolerant (positive SPT, but tolerant to peanut ingestion). In the peanut allergy group, the median age of first allergic presentation was at 24 months. The rate of anaphylactic reactions in the study population was 7.1%. In the peanut allergy group, 32.3% were also sensitized to the following tree nuts: cashew nut (17.1%), almond (15.6%), hazelnut (15.6%), walnut (14.1%).	(70)
Singapore Philippines	Administration of a questionnaire to assess prevalence of peanut and tree nut allergy in Singapore (local and expatriate) and Philippine schoolchildren of different age groups. Allergy diagnosis was based on convincing history which was defined by reports on the appearance of specific allergic symptoms within two hours after food ingestion.	In total, 25,692 schoolchildren responded to the survey. Of these, 23,425 children (4-6 and 14-16 years) were included in the final analysis. The analysis included 4515 local Singapore children (4-6 years old), 6498 local Singapore children (14-16 years old), 978 Singapore expatriates (4-6 and 14-16 years old) and 11434 Philippine children (14-16 years old).	Peanut “Tree nuts” including the following: Almond Brazil nut Cashew Hazelnut Macadamia Pecan Walnut (only questionnaire based)	Peanut allergy prevalence based on convincing history: Singapore (4-6 years: 0.64% Singapore (14-16 years): 0.47% Philippines (14-16 years): 0.43% Tree nut allergy prevalence based on convincing history: Singapore (4-6 years): 0.28% Singapore (14-16 years): 0.30% Philippines (14-16 years): 0.33% Higher rates of peanut and tree nut allergy were reported in Singapore expatriates: Peanut (4-6 years): 1.29% Peanut (14-16 years): 1.21% Tree nuts (4-6 years): 1.12% Tree nuts (14-16 years): 1.21 Most common reported tree nuts (decreasing order of frequency) were cashew, hazelnut, almond, walnut, macadamia, pistachio, pecan and Brazil nut.	(71)
Singapore	Patients from the allergy database at Kandang Kerbau Children’s Hospital (KKH), Singapore, with positive SPT or peanut-specific ImmunoCAP FEIA < 0.35 kUA/L were selected (2003-2006). Eligible patients completed a questionnaire. Specific serum IgE to Ara h 1, Ara h 2 and Ara h 3 was detected by ELISA. Peanut-specific IgE was detected using CAP-FEIA.	31 patients (aged 0.7-13.2 years) consented to the study (of 62 eligible patients).	Peanut (specific IgE to Ara h 1, 2, 3 was measured; commercial extracts used for SPT)	SPT wheal size of the 31 tested patients ranged from 3-17 mm. 28 patients had positive peanut-specific IgE. 87.1% had IgE specific to Ara h 1, 87.1% to Ara h 2 and 54.8% to Ara h 3.	(72)
Singapore	Retrospective study of Singaporean children that experienced anaphylaxis and visited a tertiary pediatric hospital between 2005-2009. Patients with history of anaphylaxis underwent SPT. SPT was considered positive if wheal size was ≥ 3 mm compared to the negative control.	98 children (aged 3.6-10.8 years) included in study (108 cases of anaphylaxis).	Peanut Tree nuts (commercial extracts used for SPT)	Peanut was the most common food trigger of anaphylaxis (19%). Tree nuts accounted for 4% of anaphylaxis.	(73)
Taiwan	Serum was collected and sIgE to individual nuts was measured (positive if sIgE ≥ 0.35 kUA/L) using ImmunoCAP.	333 patients (aged 2-93 years) from the outpatient department of Kaohsiung Veterans General Hospital, Taiwan that showed symptoms of asthma, atopic dermatitis and allergic rhinitis were included in the study (from 2014-2017).	Peanut Cashew Brazil nut Almond (no information on individual allergen molecules)	In total, 555 sIgE data were available, of which 339 were considered as food sensitization (≥ 0.35 kUA/L), including peanut (n = 124, 36.6%), cashew nut (n = 64, 18.9%), Brazil nut (n = 28, 8.3%) and almond (n = 73, 21.5%).	(74)
Japan	A questionnaire was provided to the participants in order to collect data on anaphylaxis-causing foods.	1383 individuals from 878 families (including 319 patients with history of anaphylaxis) provided a valid questionnaire. Average age was 11.25 years (range, 0–93 years). The most frequently recorded age was 5 years.	Peanut (only questionnaire based)	27 of 319 patients (8.5%) reported peanut-related anaphylaxis. In comparison, anaphylaxis to milk, eggs and wheat was reported by 221 (69.3%), 144 (45.1%) and 92 (28.8%) patients, respectively.	(75)
USA	Follow-up study to determine prevalence of peanut and tree nut allergy in the USA by a nationwide, cross-sectional random phone survey. Allergic reactions were considered “convincing” if specifically defined allergic symptoms were reported.	5300 households (13,534 subjects) were surveyed (children and adults from 0 to ≥65 years).	Peanut Walnut Cashew Pecan Almond Pistachio Brazil nut Macadamia (only questionnaire based)	Overall prevalence of peanut allergy (children and adults): 0.8% Overall prevalence of tree nut allergy (children and adults): 0.6% For children < 18 years the prevalence of peanut or tree nut allergy was 2.1%, compared with 1.2% in 2002 and 0.6% in 1997. Number of participants reporting tree nut allergy: Walnut: 41 Cashew: 29 Pecan: 26 Almond: 25 Pistachio: 19 Brazil nut: 19 Hazelnut: 17 Macadamia: 17	(76) Previous studies: (77, 78)
Mexico	Cross-sectional, observational, retrospective trial. Data registries (2016-2018) from an allergy laboratory in Mexico City that included patients with suspected food allergy of all ages were analyzed. Data included results of sIgE measurements using ImmunoCAP (sIgE ≥ 0.35 kUA/L for positive result).	In total, 2633 patients (of all ages and gender) were included in the serological testing. In the final analysis, 1795 patients with suspected clinical allergy were included.	Hazelnut Peanut Almond Cashew Pecan (no information on individual allergen molecules)	Hazelnut, peanut and almond were among the 15 most frequent foods with positive sIgE (≥ 0.35 kUA/L) results (number of tested patients and % of positive results of all patients tested for this food): Hazelnut: 63, 49% Peanut: 219, 25% Almond: 65, 18% Sensitization to peanut and tree nuts was more frequent in older children (aged 6-17 years). In the group of foods with low sample size (< 50) cashew showed high positivity: of 22 patients tested, 27.3% had sIgE levels of ≥ 0.35 kUA/L and 13.6% had sIgE levels of ≥ 0.71 kUA/L. Of 34 patients that were tested to pecan, 14.7% had both sIgE levels of ≥ 0.35 kUA/L and ≥ 0.71 kUA/L.	(79)
Mexico	Prevalence of peanut and tree nut allergy in Mexican adults assessed based on a survey. Probably allergy was defined by reports of specific allergic symptoms appearing within two hours after food ingestion.	1126 participants (50.1% young adults aged 18-24 years and 49.9% adults aged 25-50 years) were included in the study.	Peanut Pecan Hazelnut Pistachio Almond (only questionnaire based)	Due to lack of documented adverse reactions to hazelnuts, pistachios, and almonds in the tree nut category perceived and probable allergy applied only for pecan and was 0.4% and 0.3%, respectively. Perceived and probably peanut allergy was both 0.6%.	(80)
Canada	Food allergy prevalence was assessed by a random telephone survey. Food allergy was either defined as perceived (self-report), probable (convincing history or reported confirmation by a physician) or confirmed (convincing medical history and confirmatory test results). Confirmatory test results included positive SPT (wheal size at least 3 mm greater than the negative control), food specific serum IgE levels of IgE ≥ 0.35 kUA/L or positive OFC. Additionally, patients that had uncertain clinical history were considered having confirmed allergy if they had positive SPT together with sIgE of ≥ 15 kUA/L for peanut and tree nut or positive SPT together with positive OFC or OFC alone.	Of 10596 households, 3613 (9667 individuals) completed interview and were included in the analysis. Participation was eligible if respondents were 18 years or older. However, respondents also provided information on any additional allergic household member.	Peanut Tree nut (not distinguished between individual tree nuts) (only questionnaire based)	Peanut allergy prevalence (%): Children: Perceived: 1.77 Probable:1.68 Confirmed: 1.03 Adults: Perceived: 0.78 Probable: 0.71 Confirmed: 0.26 Entire study population: Perceived; 1.00 Probable: 0.93 Confirmed: 0.61 Tree nut allergy prevalence (%): Children: Perceived; 1.73 Probable: 1.59 Confirmed: 0.69 Adults: Perceived: 1.07 Probable:1.00 Confirmed: 0.35 Entire study population: Perceived; 1.22 Probable: 1.14 Confirmed: 0.68	(81)
Australia	Parents completed an initial questionnaire. Detection of IgE sensitization to foods in 1-year-old infants by SPT and those with sensitization in SPT (wheal size ≥ 1 mm compared to the negative control) underwent OFC.	2848 infants (12 months old) were included in the study. Of those, 45 did not undergo SPT because they had been already tested by their doctor.	Peanut (products used not further specified)	Prevalence of sensitization to peanut was 8.9% (wheal size ≥ 1 mm). Prevalence of clinically relevant sensitization (SPT ≥ 3 mm) to peanut was 6.4%. Peanut allergy prevalence confirmed by OFC was 3.0%.	(49)
Australia	At age 1 year: Tree nut sensitization was defined by SPT wheal size of at least 3 mm (compared to the negative control) to almond, cashew or hazelnut. Tree nut tolerance was defined by history of tolerance to food ingestion or negative SPT. Parent reported tree nut allergy was defined by reports of specific allergic reactions. No OFC for tree nuts was performed at age 1, but OFC performed for peanut. Sensitized tolerance to peanut was defined by SPT wheal size of at least 2 mm and negative OFC. Peanut allergy was defined by SPT wheal size of at least 2 mm and positive OFC. At age 6 years: Tree nut sensitization was defined by SPT with wheal size of at least 3 mm (compared to the negative control) to almond, Brazil nut, cashew, hazelnut, macadamia, pecan, pistachio or walnut. Definite tree nut allergy was defined by positive OFC and IgE sensitization or history of objective symptoms or positive OFC at age 4 years and SPT wheal size of 8 mm at age 6 years. Probable tree nut allergy was defined by SPT response of at least 8 mm, without reaction history or previous OFC result, SPT wheal size of 3-7 mm at age 6 years together with positive OFC at 4 years of age, history of objective symptoms or report of food avoidance due to allergy. Tree nut tolerance was defined by negative OFC result, SPT wheal size of 0-2 mm, SPT response of 3-7 mm and reported food ingestion, or lack of reaction since age 4 years without food avoidance.	Initially, 5276 1-year-old children were recruited. 3232 participated in the follow-up study at age 6 years and completed questionnaire and SPT assessment, while 1222 completed questionnaire only.	Cashew Almond Hazelnut Pistachio Walnut Macadamia Pecan Brazil nut (extracts for SPT)	Of the 5276 infants that participated in the study, 924 had positive SPT results to egg, sesame, peanut, shrimp or cow´s milk. The positive-tested infants further attended OFC clinic and had SPT to tree nuts. Food allergy to egg, peanut or sesame was confirmed by OFC in 530 patients. Tree nut sensitization at age 1 year: Of patients with challenge-confirmed food allergy, 31% were sensitized to at least 1 tree nut. Tree nut sensitization was more common in infants with both peanut and egg allergy. Tree nut sensitization at age 6 years: 234 children were sensitized to tree nuts at the age of 6, corresponding to 7.3% of all that underwent SPT to tree nuts (n = 3232). 154 children were considered allergic to at least one tree nut. Cashew was the most common tree nut causing allergy (2.7%), followed by hazelnut (0.9%) and almond (0.3%). Other tree nuts allergies were diagnosed in < 1.0% of the subjects (pistachio, n = 50; walnut, n = 28; macadamia, n = 12; pecan, n = 8; and Brazil nut, n = 5).	(82)
Australia	Preselection by questionnaires for students and parents. Clinical evaluation in eligible students by SPT and OFC in case of SPT result with wheal size of at least 3 mm. Current clinical food allergy was defined by positive OFC or convincing history including data on IgE sensitization (SPT wheal size of > 3 mm or sIgE > 0.35 kUA/L), or SPT with wheal size of > 8 mm.	9816 randomly selected students (aged 10-14 years) provided either a student questionnaire (history of food allergy) or a parent questionnaire (history of food allergy and additional information). 5016 students were included in the clinical evaluation.	Peanut Tree nuts: Cashew Pistachio Walnut Hazelnut Macadamia Pecan Almond Brazil nut (products used not further specified)	Clinical-defined current food allergy in the clinical group (n = 5016) had a prevalence of 4.5%. The most common foods causing allergy in the clinical group were peanut (2.7%) and tree nuts (2.3%). Among tree nuts, cashew was most prevalent (1.6%), followed by pistachio (1.0%), walnut (0.7%), hazelnut (0.7%), macadamia (0.2%), pecan (0.2%), almond (0.1%) and Brazil nut (0.1%).	(83)
South Africa	Evaluation of IgE sensitization to several allergen molecules by using an allergen microarray (ISAC technology-based). Values ≥ 0.1 ISU were considered positive.	166 black South African children (aged 9-38 months) from urban and rural areas with and without atopic dermatitis (AD) were included: Urban AD (n = 32) Urban non-AD (n = 40) Rural AD (n = 49) Rural non-AD (n = 45)	Peanut (tested for individual allergen molecules)	31% of urban and 41% of rural AD patients were sensitized to at least one peanut allergen. However, self-reported peanut exposure was significantly higher in urban (79%) than rural (39%) regions. In non-AD children sensitization was significantly lower. Ara h 2 (29% rural, 19% urban AD children) and Ara h 6 (25% rural, 22% urban AD children) were most commonly recognized.	(84)
Zimbabwe Sweden	Sera from peanut-sensitized and peanut-allergic patients were analyzed for IgE to Ara h 1-3, 6, 8 and 9 using an allergen microarray. IgE levels were considered low (0.35-1 ISU-E), moderate-high (> 1-15 ISU-E) or very high (> 15 ISU-E). Allergen-specific IgE to peanut extract was measured by ImmunoCAP (≥ 0.10 kUA/L for positive result).	54 peanut-sensitized patients from Zimbabwe (aged 0.9-59 years), 25 peanut-allergic (aged 3-15 years) and 25 peanut-sensitized, but tolerant patients (aged 3-18 years) from Sweden were included.	Peanut (tested for individual allergen molecules)	46% of African patients and all of the peanut-allergic Swedish patients had IgE to at least one highly allergenic peanut allergen (Ara h 1, 2, 3, 6 or 9). Of the African patients, 48% showed IgE toward cross-reactive carbohydrate determinants (CCDs). 60% of Swedish peanut-tolerant patients had IgE to Ara h 8.	(52)

Listed are studies investigating prevalences of allergy to different nuts as determined by different methodologies in different populations with the corresponding references.