The prevalence of fish and shellfish allergy: A systematic review

Harriet Moonesinghe, Sally Kilburn, Kellyn Lee, Heather Mackenzie, Paul Turner, Carina

Venter and Tara Dean.

Corresponding Author: Dr Heather Mackenzie, Graduate School, University of

Portsmouth, Portsmouth,

Funding sources:

Clinical implications:

Capsule summary:

Key words: prevalence, fish, shellfish, food allergy, food hypersensitivity, systematic

review

ABSTRACT

Background: Accurate information on the prevalence of food allergy facilitates a more

evidence-based approach to planning of allergy services, and can establish important

geographical variations which may exist.

Objective: To perform a systematic review to assess the prevalence, by age, of fish,

crustacean and mollusc allergy worldwide.

Methods: Searches were conducted using two databases; Web of Science and PubMed.

Data was presented by method of diagnosis; questionnaire-based, sensitisation rates and

food challenge proven prevalence.

Results: A total of 7333 articles were identified but only 61 studies met the inclusion

criteria and were included in this review. The prevalence of fish allergy ranged from 0-7%

and shellfish allergy from 0-10.3%, depending on the method of diagnosis.

Conclusions: Very few studies have established the prevalence of fish/shellfish allergy

using the gold standard challenge criteria, with the majority instead relying on self-

reported, questionnaire-based methods. Where food challenges were used, the prevalence

for fish allergy was found to be 0-0.3% and for shellfish allergy was 0-0.9%.

INTRODUCTION

1

Fish and shellfish (crustacea) are major allergens as defined by the European Community,

and are a leading cause of anaphylaxis (1). Allergic reactions to seafood are usually

immediate i.e. related to an IgE response, although non-IgE mediated reactions (including

Food Protein Induced Enterocolitis syndrome) can also be triggered (2). Reactions can be

triggered by direct ingestion or skin contact, or (in some cases) through ingestion or

contact with cooking vapours (3). In contrast to allergens such as egg and cow’s milk,

seafood allergy does not in general resolve with age and therefore life-long dietary

avoidance is necessary (4). Evidence suggests that there is an increased prevalence of fish

and shellfish allergy in countries with high seafood consumption such as Australia, Asia

and parts of Europe (5).

Accurate information about the prevalence of allergies to specific foods facilitates an

evidence-based approach to the planning and provision of allergy services both nationally

and internationally (2). Prevalence data can be used to identify which are the most

common food allergens and their natural history within countries. At an international level,

geographical variations can be explored and greater understanding of trends and

mechanisms in the development of food allergy reached. Existing policy and legislation in

the field of food allergy (e.g. manufacturing and labelling practices, care guidelines,

catering practices) is largely informed by self-reported prevalence, which is widely

recognised to overestimate true prevalence (6).

A systematic review enables the totality of the evidence base to be reviewed. This would

provide an accurate description of what we currently know about the prevalence of

allergies to specific foods and identifies gaps in our understanding (e.g. where data is

lacking for countries, diagnostic method and/or allergen). It allows us to understand the

degree to which current knowledge is based on self-report, sensitisation and/or challenge-

proven food allergy.

There are currently four existing systematic reviews looking at prevalence of food allergy

(7). However no systematic review has yet to describe the prevalence of allergy to the 14

food allergens as listed under EU food labelling legislation (which is the most

comprehensive list in current use) by region of the world. Therefore we conducted a

systematic review to meet the above aims, and this paper is part of a series presenting data

from this. This paper will report the prevalence of fish and shellfish allergy.

METHODS

2

Search strategy and reference management

We searched Web of Science, PubMed and the Conference Proceedings Citations Index

(Online repository 1). No language, date or study type restrictions were employed. Grey

literature was sought via direct contact with a list of topic experts and relevant research

funders. Search results were managed using EndNote and duplicates removed. English

language versions of articles were obtained where necessary.

Screening

The titles and abstracts of all identified articles were screened by one review author and

excluded if, for example, they were obviously unrelated to the topic of the review, the

sample was inappropriate for the scope of the review, or because they did not present

primary research. If the review author was unsure about the eligibility of the paper for

inclusion in the review, the paper was discussed with another author. Reasons for

exclusion were recorded. The full-text of all potentially eligible studies was assessed

against the following criteria:

Types of studies

Population-based cross-sectional studies and cohort studies examining the prevalence of

food allergy (IgE-mediated and non-IgE mediated) at an identifiable point (or period) in

time.

Types of participants

Participants of all age groups from any country. Studies that did not present region or

country-specific data were excluded from the review. Studies must have been population

based, using either a fixed cohort or an appropriate sampling strategy. Studies conducted in

a clinical setting or in selected patient groups were excluded.

Types of outcome measure

Prevalence of allergies (or sensitisation) to one or more of the following food allergens

(milk/dairy, eggs, cereals, peanuts, nuts, celery, crustaceans, fish, molluscs, soy, lupin,

mustard and sesame) were eligible for inclusion as diagnosed by:

Self-report

Positive SPT

3

Positive serum-specific IgE

Clinical history of adverse reactions to foods and:

; positive SPT (for IgE-mediated food allergy)

; or positive serum-specific IgE (for IgE-mediated food allergy)

; or positive food challenge (open or double-blind placebo-controlled: for IgE and

non-IgE mediated food allergy, allowing for delayed reactions in the case of non-

IgE mediated food allergy)

Studies that did not present separate prevalence data for individual allergens were excluded

from the review. In addition, studies employing atopy patch tests or other diagnostic tests

e.g. IgG measures were excluded as these are not recommended for the routine diagnosis

of food allergy (8).

Data extraction and analysis

The following was extracted for all included studies (using EPPI Reviewer software; EPPI

Centre, 2011):

1. General information: Authors’ contact details, research funder, year(s) study

conducted, country/countries in which conducted.

2. Methods: Study design, type of food allergy considered, food(s) assessed, method

of diagnosis (including additional information with regard to the procedure),

sampling strategy and sample characteristics.

3. Outcomes: Percentage prevalence, raw data and confidence intervals.

Where there was ambiguity in the reporting of results, all efforts were made to contact the

study authors to provide additional information.

Assessing the quality of included studies

Studies were assessed as being at low, medium or high risk of bias on the basis of two

quality criteria: risk of bias of the diagnostic method (in studies utilising more than one

method of diagnosis, the risk of bias of the highest quality method was judged) and method

of sampling.

Data synthesis and presentation

4

For each allergen we have presented a forest plot which maps the data (percentage

prevalence and 95% confidence intervals, where possible) according to region and country

and then by age (this has been grouped however is meaningful dependent upon the

approach taken by the included studies). The prevalence data has been presented by

method of diagnosis, and information has also been included on the year and age group for

which data is being presented. Data has additionally been narratively reported for the

prevalence of allergy to fish and shellfish both across Europe and for countries outside of

Europe. Meta-analysis was not conducted due to the high heterogeneity between studies

and so a pooled estimate would have been misleading.

RESULTS

Results of the search

Of the 7333 papers identified by the search 7145 were excluded during the title and

abstract screening. Hence, the full-text was obtained for 216 papers, of which 116 were

excluded after screening (further details of the process and reasons for exclusion are

outlined in Figure 1). There were 100 studies that were included in the systematic review,

of which there were 61 studies identified which presented data on the prevalence of fish

and/or shellfish allergy.

5

Figure 1 Flowchart of search results and screening for all studies

Description of included studies

The majority of studies (48) employed a cross-sectional design and 13 studies used a

cohort design. Forty-one studies were based in a paediatric population (< 18 years old), 11

in adults (> 18 years old), and in nine studies all ages were presented collectively. Figure 2

illustrates where the included studies were conducted. The key characteristics as well as

further information about the method of diagnosis of these studies are shown for each

country in alphabetical order (online repository). Questionnaire-based methods for

6

OF WHICH PRESENTED DATA ON

FISH/SHELLFISH = 61

INCLUDED= 100

MAIN REASON

Study design= 23

Topic= 16 Unidentifiable

time point= 4 Sample= 24 Unidentifiable

allergen= 1 Method of

diagnosis= 2 Data not

presented by individual allergen= 15

Linked records (i.e. data presented elsewhere= 26

Cannot obtain study record= 5

EXCLUDED= 116SCREENED ON FULL TEXT= 216

EXCLUDED= 7117SCREENED ON TITLE AND ABSTRACT= 7333

ADDITIONAL PAPERS IDENTIFIED (e.g. from

contact with expert panel)= 10

DUPLICATES REMOVED= 2484

RESULTS FROM DATABASE SEARCH= 9807

assessing suspected fish and/or shellfish allergy were presented in 44 studies, 25 studies

measured sensitisation rates, and ten studies carried out food challenges to confirm fish

and/or shellfish allergy.

7

Figure 2 A map of the world showing the countries from which prevalence data was found Online repository (purple pins= Europe, orange pins= rest of the world

8

Risk of bias in included studies

Table 2 presents the quality assessment for all included studies.

Table 1 Quality assessment of included studies

Study IDDiagnostic Methods: risk

of bias

Sampling Strategy

Method: risk of bias

Al-Hammadi (2010)

Arshad (2001)

Ben-Shoshan (2010)

Branum (2009)

Brugman (1998)

Burney (2010)

Chen (2011)

Connett (2012)

Dalal (2002)

Eggesbo (1999)

Emmett (1999) N/R

Falcao (2004)

Gelincik (2008)

Greenhawt (2009)

Gupta (2011)

Haahtela (1980)

Hu (2010)

Jansen (1994)

Johansson (2005)

9

Study IDDiagnostic Methods: risk

of bias

Sampling Strategy

Method: risk of bias

Kajosaari (1982)

Kavaliunas (2012)

Kim (2011) N/R

Krause (2002)

Kristjansson (1999)

Lao-araya (2012)

Leung (2009)

Liu (2010)

Marklund (2004)

Marrugo (2008)

Martinez-Gimeno

(2000)Mustafayev (2012) N/R

Obeng (2011) N/R

Oh (2004)

Orhan (2009)

Osborne (2011)

Ostblom (2008 a) N/R

Ostblom (2008 b) N/R

Osterballe (2005)

Osterballe (2009)

Penard-Morand

(2005)Pereira (2005)

10

Study IDDiagnostic Methods: risk

of bias

Sampling Strategy

Method: risk of bias

Pyrhonen (2009)

Rance (2005)

Ro (2012) N/R

Roberts (2005)

Sakellariou (2008)

Santadusit (2005)

Schafer (2001)

Shek (2010)

Sicherer (2004)

Touraine (2002)

Van Bockel-

Geelkerken (1992)

N/R

Venter (2006)

Venter (2008)

Vierk (2007)

Von Hertzen (2006)

Woods (1998)

Wu (2012)

Young (1994)

Zannikos (2008)

Zuberbier (2004)

11

High risk of

bias

Medium risk of

bias

Low risk of

bias

1) Low risk of bias= food challenges (open or double-blind) with or without clinical history; Medium

risk of bias= sensitisation (skin prick test and/or serum-specific IgE) with clinical history; High risk

of bias = Sensitisation (skin prick test and/or serum specific IgE) without clinical history,

questionnaire-based methods (self-report, clinical history or clinician diagnosed)

2) Low risk of bias = whole population; Medium risk of bias= random; High risk of bias = non-random

12

13

Figure 3 Fish allergy prevalence in Europe diagnosed by questionnaire-based methods

14

Figure 4 Fish allergy prevalence in other regions of the world diagnosed by questionnaire-based methods

15

Figure 5 Fish allergy prevalence in Europe diagnosed by sensitisation methods

Figure 6 Fish allergy prevalence in other regions of the world diagnosed by sensitisation methods

16

Figure 7 Fish allergy prevalence in Europe diagnosed by food-challenge methods

17

Figure 8 Fish allergy prevalence in other regions of the world diagnosed by food-challenge methods

18

Fish Allergy Prevalence

Assessed using questionnaire-based methods

In Europe, the highest reported prevalence in adults was found in Greece with 1.5%

(95% CI: 1.0-2.2) (9) of 20-54 year olds reporting an adverse reaction to fish and the

lowest reported prevalence was seen in Denmark, with only 0.2% (95% CI: 0.0-1.0)

(10) of 22 year olds reporting an adverse reaction to fish (cod specifically). With

regards to children, the prevalence ranged from 7.0% (95% CI: 5.4-9.0) (11) in one

year olds in Finland to 0.0% (95% CI: 0.0-0.1) (12) of 0-2 year olds in Israel.

In the African region one study reported fish prevalence data in Ghana and found the

reported prevalence of 5-16 year old children to be 0.3% (95% CI: N/R) (13).

In the Americas region, the highest reported fish allergy in adults was seen in the

United States (2.7%, 95% CI: 1.6-4.7) (14) and the lowest was 0.12% (95% CI: 0.08-

0.16) in Canada (15)1. The highest prevalence for children was 0.2% (95% CI: 0.1-

0.5) (16) in the United States and the lowest prevalence found in Canada was 0.0%

(95% CI: N/R) (15).

One study identified from the Eastern Mediterranean region of the world reported that

the clinician diagnosed prevalence of fish allergy in children (6-9 years old) was 2.8%

(95% CI: 1.5-5.1) (17).

In the South East Asia region, the highest reported prevalence seen in Thailand was

1.1% (95% CI: 0.4-2.7) (18) for 3-7 year olds, compared to the lowest which was

0.3% (95% CI: 0.1-1.2) (19) of 6 month- 6 year olds also in Thailand.

In the Western Pacific region of the world the reported prevalence of ‘fish/shellfish’

in 20-44 year olds in Australia was 2.1% (95% CI: 1.2-3.6) (20). In Taiwan in over 19

year olds, the prevalence was lower at 1.2% (95% CI: 1.0-1.4) when a clinician

diagnosis of fish allergy was used (21). The reported prevalence of childhood fish

allergy ranged from 4.3% (95% CI: 4.0-4.7) (22) in 14-16 year olds in the Phillipines

to 0.2% (95% CI: 0.1-0.5) (23) of 2-7 year olds in Hong Kong.

1 Ben-Shoshan (2010) prevalence and confidence interval are reported to two decimal places, as it was not possible to calculate the prevalence based on raw data and therefore we report as per the study.

19

Assessed using sensitisation

In Europe one study in Germany used SPT in an adult population (25-74 year olds)

showing 2.9% (95% CI: 2.2-3.9) (24) sensitisation to mackerel. In children the highest

sensitisation rate was found in Finland, where 2.7% (95% CI: 1.7-4.2) (25) of 15-17

year olds were sensitised to fish and the lowest sensitisation rate was seen in the

United Kingdom, where 0.0% (95% CI: 0.0-0.3) (26) of seven year olds were

sensitised to fish (cod specifically).

One study in the Americas region measured sensitisation using serum-specific IgE

tests and found that 0.0% (95% CI: 0.0-5.3) (27) of 20-44 year olds were sensitised to

fish.

The same study found 0.0% (95% CI: 0.0-2.1) (27) fish sensitisation in 20-44 year

olds in Australia. For children the sensitisation rate ranged from 0.2% (95% CI: 0.0-

1.4) (28) to 0.8% (95% CI: 0.2-2.5) (29) in China.

Assessed using clinical history and sensitisation

In Europe the highest prevalence was seen in Norway where 1.1% (95% CI: 0.4-3.1)

(30) of two year olds were sensitised to fish and the lowest was 0.0% (95% CI: 0.0-

0.1) (12) of 0-2 year olds in Israel. Adult fish allergy prevalence ranged from 0.8%

(95% CI: 0.2-2.5) (27) in 20-44 year olds in Germany, to 0.0% in several other

studies.

In South East Asia the prevalence was 0.2% (95% CI: 0.0-1.0) (19) of 6 month- 6

year olds in Thailand.

Assessed using food challenges

In Europe, with regards to open food challenges, only one study in Denmark reported

data for adult fish (cod) allergy; 0.1% (95% CI: 0.0-0.8) (10) of 22 year olds. For

children, the lowest confirmed prevalence was 0.0% (95% CI: 0.0-4.2) (31) of under

three year olds in Denmark and the highest was 0.1% (95% CI: 0.0-0.8) (11) of six

year olds in Finland. When a double-blind placebo-controlled food challenge was

used, in adults the rate of confirmed prevalence ranged between 0.2% (95% CI: 0.0-

0.9) (31) in Denmark and 0.0% (95% CI: 0.0-0.1) (32) in Turkey; and in children

20

from 0.3% (95% CI: 0.0-2.0) (33) in Iceland to 0.0% in Denmark (31), Turkey (34)

and the United Kingdom (35).

In South East Asia a prevalence of 0.2% (95% CI: 0.0-1.4) (18) was found for 3-7

year olds based on an open food challenge.

21

Figure 8 Shellfish allergy prevalence in Europe diagnosed by questionnaire-based methods

22

Figure 9 Shellfish allergy prevalence in other regions of the world diagnosed by questionnaire-based methods

23

Figure 10 Shellfish allergy prevalence in Europe diagnosed by sensitisation methods

24

Figure 12 Shellfish allergy prevalence in other regions of the world diagnosed by sensitisation methods2

2 No confidence intervals were available for Liu 2010

25

Figure 11 Shellfish allergy prevalence in Europe diagnosed by food-challenge methods

26

Figure 14 Shellfish allergy prevalence in other regions of the world diagnosed by food-challenge methods

27

Shellfish Allergy Prevalence

Assessed using questionnaire-based methods

In Europe with regards to adult crustacean allergy, one study was carried out in

Denmark which found 2.0% (95% CI: 1.2-3.3) (10) self-reported allergy to shrimp. In

children the reported prevalence ranged from 5.5% (95% CI: 4.3-7.1) (36) of 5-17

year olds in France to 0.1% (95% CI: 0.0-0.5) (37) of 5-12 year olds in Lithuania. The

reported prevalence of mollusc (oyster) allergy was 1.5% (95% CI: 0.9-2.4) (36) in 5-

17 year olds in France, for octopus allergy it was 0.4% (95% CI: 0.1-1.1) (10) of 22

year olds in Denmark, and for octopus and squid allergy combined in Portugal it was

0.5% (95% CI: 0.1-1.5) (38) of 39 year olds and above.

In the African region, one study could be found from Ghana which reported shrimp

allergy prevalence in 5-16 year old children to be 0.1% (95% CI: N/R) (13).

In the Americas region, one study, carried out in the United States, specifically asked

about crustacean allergy, finding that for adults the reported prevalence was 0.7%

(95% CI: 0.5-1.0) (39).The remaining studies report on ‘shellfish allergy’ collectively.

The highest reported prevalence seen in adults was 9.0% (95% CI: 6.7-11.9) (14) and

the lowest was 1.69% (95% CI: 1.39-1.98) (15). The highest reported shellfish allergy

in children was 2.0% (95% CI: 1.7-2.5) (40) and the lowest was 0.06% (95% CI:

0.01-0.10) (15).

In the South East Asia region the highest reported crustacean allergy was 3.1% (95%

CI: 1.8-5.3) (18) of 3-7 year olds (shrimp) and the lowest was 0.7% (95% CI: 0.2-2.1)

(18) of 3-7 year olds (crab). With regards to mollusc allergy, the reported prevalence

was 0.2% (95% CI: 0.0-1.4) (18) for 3-7 year olds and for ‘shellfish’ was 0.5% (95%

CI: 0.1-1.5) (19) of 6 month- 6 year olds.

In the Western Pacific region one study reported clinician-diagnosed prevalence for

adults in Taiwan with shrimp allergy affecting 3.3% (95% CI: 3.0-3.6), crab allergy

2.3% (95% CI: 2.0-2.5) and mollusc allergy 1.5% (95% CI: 1.3-1.7) (21). Crustacean

allergy in children was reported as high as 4% (95% CI: 3.7-4.4) for shrimp allergy

and low as 0.4% (95% CI: 0.1-1.2) for crab allergy (21). Mollusc allergy in children

was reported as high as 1.1% (95% CI: 1.0-1.3) in 4-18 year olds and low as 0.1%

(95% CI: 0.0-0.8) in under threes and (21).

28

Assessed using sensitisation

In Europe for crustacean allergy the highest sensitisation rate was reported in Italy in

adults (10.3%, 95% CI: 7.0-14.9) and the lowest in Switzerland (0.0%, 95% CI: 0.0-

2.3) (27).

In the Americas region the highest sensitisation rates were 6.1% (95% CI: N/R) (41)

of 6-19 year olds and 6.7% (95% CI: N/R) (41) of 40-59 year olds, and the lowest

were 5.2% (95% CI: N/R) (42) of under 18 year olds and 0.0% (95% CI: 0.0-5.3)

(27)of 20-44 year olds.

In the Western Pacific region, adult shrimp sensitisation was reported to be 2.3%

(95% CI: 0.8-5.5) (27) in Australia and in children the latest data from China

indicated it was 0.3% (95% CI: 0.0-1.7) (29).

Assessed using clinical history and sensitisation

In Europe when a clinical history was combined with a positive SPT result, a

prevalence rate of 0.2% (95% CI: 0.1-0.5) was found for crab allergy and 0.0% (95%

CI: 0.0-0.2) for mussel allergy, in all ages in Germany (43).

In the South East Asia region the sensitisation rates (including a clinical history) for

both shrimp and ‘shellfish’ were 0.3% (19).

Assessed using food challenges

Two studies in Europe (Denmark) utilised food challenges to confirm the prevalence

of shellfish allergy. Open food challenges were conducted by both studies and showed

a shrimp allergy confirmed prevalence rate of 0.0% (95% CI: 0.0-4.2) (31) for under

threes, 0.2% (95% CI: 0.0-1.0) (10) for 22 year olds, and an octopus allergy

confirmed prevalence rate of 0.1% (95% CI: 0.0-0.8) (10) for 22 year olds. One study

carried out double-blind placebo-controlled food challenges to shrimp which showed

a confirmed prevalence of 0.0% (95% CI 0.0-1.0) in three year olds and 0.3% (95%

CI: 0.1-1.0) adults (31).

In South East Asia challenge proven prevalence ranged from 0.3% (95% CI: 0.1-1.2)

(19) to 0.9% (95% CI: 0.3-2.4) (18) for shrimp allergy, and 0.2% (95% CI: 0.0-1.4)

(18) for crab allergy.

29

DISCUSSION

In summary, with regards to fish allergy, the reported prevalence assessed by

questionnaire-based methods ranged from 0.0% to 7.0%, sensitisation rates identified

in this review were between 0.0% and 2.9% and food challenge confirmed prevalence

rates were between 0.0% to 0.3%. With regards to shellfish allergy, the reported

prevalence assessed by questionnaire-based methods was 0.1% to 5.5% for crustacean

allergy, mollusc allergy ranged from 0.4% to 1.5%, and shellfish allergy was reported

in the range of 0.1% to 1.5%. Sensitisation rates ranged from 0% to 10.3% to

crustacean and 0% to mollusc and food challenges confirmed a 0% to 0.9%

prevalence of crustacean allergy and 0.1% prevalence of mollusc allergy.

We found a higher range of reported fish allergy prevalence compared to that of a

previous review (7) which found that the variation in reported prevalence of fish

allergy ranged from 0% to 2%. This is due to our inclusion of more recent studies,

including those from outside Europe; the higher prevalence’s in the current review

come from studies which have not been included in the review conducted by Rona et

al (7) (Kajosaari 1982; Kristjansson 1999; Martinez-Gimeno 2000; Mustafayev 2012;

Pyrhonen 2009; Touraine 2002; Young 1994). Sensitisation and food-challenge

confirmed fish allergy prevalence rates were similar to those reported previously

(0.5% or less and 0.4% respectively) (7). Rona et al (7) report a higher range of self-

reported shellfish allergy (0%-10%) due to their inclusion of a study which did not

meet the inclusion criteria for this review. We also found a higher rate of sensitisation

(GIVE DATA), due to our inclusion of more recent studies.

Our data suggest that the reported prevalence of fish and shellfish allergy is slightly

higher in children than in adults, however this could be due to the relative small

number of adult studies available for analysis which could result in an underestimate

of prevalence. More studies are needed to explore the self-reported prevalence of fish

allergies in adults across the world as the notion that fish allergy is more prevalent in

adults than children may not be accurate.

There was a significant paucity in food challenge data worldwide which makes

comparisons between children and adults, and different regions of the world

challenging. The limited data available suggests that fish allergy prevalence are

similar worldwide however shellfish allergy prevalence is higher in the South East

30

Asia region, perhaps due to the high consumption of shellfish in the local diet. Very

few studies investigated mollusc allergy, with the majority looking at crustacea or

shellfish combined (the study did not distinguish between crustacean and mollusc

allergy); further studies are needed which measure the prevalence of this allergy.

A strength of the current review is the rigorous search strategy used to identify

potential studies for inclusion. In addition, experts within the field of food allergy

epidemiology were contacted to ensure thoroughness of literature searches and in the

extraction and interpretation of the data. In most cases, we were able to present the

raw data from the studies and calculate the prevalence and 95% confidence intervals

to avoid misreporting. Nonetheless, there are some limitations to the current review:

we are aware that some potentially eligible studies were excluded due to the lack of

clarity of the results, and despite every efforts being made to contact the study

authors’ for clarity, not all responded to our request and thus the studies had to be

excluded from the review.

The current study provides comprehensive and up to date estimates of fish and

shellfish allergy across age groups and regions of the world. There is some evidence

to suggest that the prevalence of fish and shellfish allergy varies according to age and

region. However, there is a marked scarcity of high quality prevalence studies for fish

and shellfish allergy; only ten were included in the present review. Future research

should utilise more rigorous diagnostic methods and be conducted across all regions

of the world in both children and adults.

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