This study is novel since it was conducted in a small town, and in a population of preschool age children, thereby having populational features which are often overlooked by many studies on food allergies. The prevalence of reported food allergies after applying the screening questionnaire was 11.7% but it dropped to 0.97% when a more thorough, confirmatory, validated questionnaire was applied.
The frequency of reported food allergies detected in our study by the screening questionnaire (11.7%) was within the range reported by other similar studies. In fact, prevalence results obtained in such studies have been quite variable ranging from 17.6%, as reported in another Brazilian study done in the southeast region with preschoolers , to 5.6%, as described in a Portuguese study also with preschoolers of bigger cities . Both of these studies also resulted from questionnaires and involved preschool age children, while a meta-analysis with 23 selected studies described a variation in the prevalence of reported food allergies from 3 to 35% . However, when we applied the second, confirmatory questionnaire (Q2), the prevalence of reported food allergy dropped to 0.97%, a value that is clearly lower than that observed in other similar studies for the same age range .
This clear discrepancy in the prevalence of food allergies between the screening and Q2 questionnaires suggests an overestimation of prevalence of food allergies by self-report, using short screening tests, in population studies. The huge difference observed after applying a confirmatory questionnaire is probably not due to memory bias since only a short time elapsed between applying both questionnaires. It thus seems to be based on the false perception of the presence of allergy to some foods considered unhealthy in a given culture and the low level of understanding on the part of the parents/guardians who answered the self-administered screening questionnaire. The low agreement between the findings of the screening questionnaire and the detailed questionnaire may further reiterate the importance of understanding the cultural aspects of the population in the direct approach of a patient suspected of food allergy, highlighting the importance of medical history, complementary tests and oral food challenge to confirm the diagnosis.
Various factors may account for the low prevalence of reported food allergies in our study, as detected by the Q2 questionnaire. First of all, cultural factors may play a part. With regard to cultural aspects, self-administered questionnaires enable a wide range of understandings, given the multidimensionality and complexity of the intercultural facets of communication. Among those surveyed, from a cultural viewpoint, a range of interpretations may arise in parents/guardians, after analysis of the questions asked in the questionnaire, and this may vary significantly between the population groups. In fact, issues such as knowledge regarding ancestors, religion and access to information are just some of the factors that influence the answers to these questionnaires. Thus, cultural aspects strongly influence results found by qualitative and quantitative research including self-reported data . Secondly, socio-demographic factors may also have influenced our questionnaire results.
The region under study has a low human development index (0.663), with 45.2% of the population living on less than US$101 per capita a month. These specific characteristics of the region may have impacted on the results of this research since the variety of foods offered during childhood is also restricted , which may imply that children in such small cities receive less exposure to foods that are potentially more likely to trigger food allergies. Thirdly, it is also possible that the comparatively low level of reports of food allergies in the preschoolers in our study may be due to misunderstandings regarding the concepts of food allergy, since literacy levels are low in the region . Finally, it is possible that the low prevalence of reported food allergy in preschoolers in our study may be due to the fact that the study region has a high prevalence (60.0% to 64.2%) of intestinal parasites for the age group studied [18, 19]. A high early exposure of a child to intestinal parasites may provide protection against allergic diseases .
Regarding our results on specific food allergies that were reported in the screening questionnaire, some aspects should be highlighted.
With regard to the foods mentioned in the screening questionnaire, the finding of only 1.7% prevalence of reported allergy to milk in the present study may be due to the fact that 54.51% of the children studied were aged over 4 years, an age group in which most children who present symptoms of CMPA have already developed a tolerance towards cow's milk .
The high prevalence of reported pork allergy (3.6%) among the study participants differs from previous literature . In the region where the present study was conducted, there is a negative cultural perception about certain foods, such as pork. The main religion practiced in the region is Catholicism (80%), the second is evangelical (11%), both based on Christianity and, according to studies, with a possible influence of Judaism on new Christians . There is a strong cultural bias in the local population that attributes impurity to pork. This rejection of food may therefore have led to a high number of positive responses. This fact is corroborated during the direct application of the detailed questionnaire by stating a refusal to eat pork.
Mollusks and shrimps were independently reported as causing food allergies in 15 (3.6%) participants, since they are highly perishable, and are related to frequent acute infectious complications, a fact commonly confused with allergy, which leads many families to avoid consuming these foods. Sulfite, a food additive used in the process of preparing shrimps for storage, is also usually related to adverse reactions , which may increase the impression of allergy to shrimp. In addition, due to its relative distance from the sea, the consumption of seafood in Limoeiro is lower than in coastal regions of the state of Pernambuco, especially among low-income families, such as those who participated in the study, due to the high costs. These factors seem to have contributed to a false impression of a food allergy to mollusks and shrimps in this study, with a subsequent denial in the detailed questionnaire off consuming these types of food.
Among fresh fruits, it is of note that allergy to these food items is more common in regions with a high incidence of pollen, due to immunologically-driven cross-reactivity, an uncommon fact in the studied area . It is important to note that, among the aforementioned types of fruit, acai is rarely mentioned in food allergy studies, and is common in the cuisine of the Northern region of Brazil. This food was introduced to the Northeast region and its consumption has increased over the past 10 years. Recent research has suggested its insertion into the group of food allergens . Among the aforementioned fruits, bananas and avocados are classically related to cross allergy with latex , while there are reports in the literature of contact dermatitis with guava , although with no solid references to food allergy.
Previous studies have reported that the majority of studied children react to 1 or 2 food allergens, with multiple sensitization being more uncommon . In the present study, reports of allergy to multiple foods occurred more frequently among those who mentioned shrimps, pork and mollusks in the screening questionnaire, thereby emphasizing, as mentioned above, the importance of cultural perception when analysing the replies. Reports of multiple food allergies was not supported after applying the detailed questionnaires. This fact leads us, therefore, to the limitation of the screening questionnaire in separating adverse food reactions and actual food allergy, and to the importance of confirmatory tests.
Our study has various limitations. First of all, an important limitation was the fact that 24.1% of the participants who reported the presence of a reaction to food in the screening questionnaire did not continue the study. A high dropout rate is, in fact, something common in population-based studies , especially those involving several stages. Despite this, the sample size in our study remained sufficient to achieve statistical representativeness. Secondly, this is a report-based study of prevalence and may be influenced by memory bias . Thirdly, this study was only carried out in a single city and results may not be directly generalizable to other similar cities in Brazil or elsewhere.
In conclusion, this study highlights the low frequency of reported food allergy in poor areas. Despite its limitations, it throws a light in the importance of confirming food allergy before food intake (Additional file 1) restrictions. More studies are needed to complement the data obtained.