Abstract

We investigated the prevalence of asthma and factors related to asthma development in schoolchildren aged 6 to 14, living in central and peripheral areas of the city of Montes Claros, Minas Gerais and who were registered with the Family Health Strategy program. Initially, a standard written questionnaire, based on ISAAC (International Study of Asthma and Allergies in Childhood), was administered to collect personal data, information regarding income, asthma prevalence, allergic rhinitis and eczema (N = 1,131). Secondly, a case-control study was performed by grouping the patients as either asthmatic (A; N = 172) or non-asthmatic (NA; N = 379). Potential factors associated with the occurrence of asthma were evaluated using the complementary questionnaire from ISAAC phase II. Skin tests for immediate hypersensitivity (STIH) and parasitological tests were also performed. The odds ratio, estimated by multivariate analysis, indicated that asthma cases were related to kindergarten attendance, household smoking, family history of asthma, rhinitis and positive STIH. It was concluded that, in the studied population, the prevalence of asthma was related to genetic predisposition, in addition to individual history, social demographics, exposure to pollutants such as tobacco smoke and a positive response to allergy testing.

Asthma; Allergens; Rhinitis; Eczema

Introduction

Allergic diseases are defined as global health problems affecting both developed and non-developed countries, and are responsible for individual suffering and high socioeconomic burden¹1. Ring J. Davos Declaration: allergy as a global problem. Allergy 2012; 67(2):141-143.. In particular, asthma is the most common chronic disease of the respiratory tract in children²2. World Health Organization (WHO). Asthma: fact sheet # 307. Geneva: WHO; 2013., causing morbidity and decreased quality of life for both patients and relatives¹1. Ring J. Davos Declaration: allergy as a global problem. Allergy 2012; 67(2):141-143.. There have been many recent advances in the understanding of asthma etiology and the mechanisms involved in asthma pathophysiology, as well as the development of new treatments. However, studies conducted in different countries suggest that asthma prevalence is increasing in children and teenagers³3. O’Byrne PM. Global guidelines for asthma management: summary of the current status and future challenges. Pol Arch Med Wewn 2010; 120(12):511-517..

Asthma is a serious public health problem, with both social and economic impacts, since it overloads health services. Recent estimates indicate that asthma affects 334 million people worldwide⁴4. Global Asthma Network. The Global Asthma Report 2014. Auckland: Global Asthma Network; 2014.. In Brazil, asthma is diagnosed in over 20% of children and young people between 7 and 14 years⁵5. Chong-Neto HJ, Rosário NA, Solé D, Latin American ISAAC Group. Asthma and rhinitis in South America: how different they are from other parts of the world. Allergy Asthma Immunol Res 2012; 4(2):62-67.. The age of asthma development can be determined by genetic factors in 34% of cases and by environmental factors in 66%⁶6. Thomsen SF, Duffy DL, Ohm KK, Backer V. Genetic influence on the age at onset of asthma: a twin study. J Allergy Clin Immunol 2010; 126:626-630.. However, as the innate and adaptive immune responses remain immature in pre and postnatal life, individuals are more susceptible to asthma and similar diseases during childhood⁷7. Szefler SJ. Advances in pediatric asthma in 2010: addressing the major issues. J Allergy Clin Immunol 2011; 127:102-115..

Epidemiological studies are often used to monitor prevalence trends, to determine the associated factors and severity of allergic diseases, especially asthma and allergic rhinitis⁸8. Mallol J, Solé D, Asher I, Clayton T, Stein R, Soto-Quiroz M. Prevalence of asthma symptoms in Latin America: the International Study of Asthma and Allergies in Childhood (ISAAC). Pediatr Pulmonol 2006; 30(5):439-444.

9. Barreto ML, Ribeiro-Silva RC, Malta DC, Oliveira-Campos M, Andreazzi MA, Cruz AA. Prevalência de sintomas de asma entre escolares do Brasil: Pesquisa Nacional em Saúde do Escolar (PeNSE 2012). Rev Brasileira de Epidemiologia 2014; 17(Supl.1):106-115.^-1010. Casagrande RRD, Pastorino AC, Souza RGL, Leone C, Solé D, Jacob CMA. Asthma prevalence and risk factors in schoolchildren of the city of São Paulo, Brazil. Rev Saude Publica 2008; 42(3):517-523.. Classic risk factors for asthma are a family history of allergic diseases, sensitization to environmental allergens (including aeroallergens), exposure to endotoxins, fungal and viral respiratory infections in early life. However, these factors do not fully explain the onset and chronicity of asthma¹¹11. Sly PD. The early origins of asthma: who is really at risk? Curr Opin Allergy Clin Immunol 2011; 11(1):24-28.. Other factors that have also been associated with asthma prevalence include male gender, low birth weight, maternal or household smoking and secondary exposure to pollution in urban areas¹¹11. Sly PD. The early origins of asthma: who is really at risk? Curr Opin Allergy Clin Immunol 2011; 11(1):24-28.. Moreover, asthma can also be aggravated by climate changes, exposure to irritant chemicals, physical exercise and emotional factors⁷7. Szefler SJ. Advances in pediatric asthma in 2010: addressing the major issues. J Allergy Clin Immunol 2011; 127:102-115.. As a means of verifying and recording trends in the prevalence and severity of asthma and allergic diseases in different countries, ISAAC (International Study of Asthma and Allergies in Childhood) has developed specific research instruments¹²12. Asher MI, Keil U, Anderson HR, Beasley R, Crane J, Martinez F, Mitchell EA, Pearce N, Sibbald B, Stewart AW, Strachan D, Weiland SK, Williams HC. International Study of asthma and allergies in childhood (ISAAC): Rational and Methods. Eur Respir J 1995; 8:483-491.. The use of a standardized ISAAC questionnaire minimizes variations in asthma prevalence estimates, allowing comparison across different locations¹²12. Asher MI, Keil U, Anderson HR, Beasley R, Crane J, Martinez F, Mitchell EA, Pearce N, Sibbald B, Stewart AW, Strachan D, Weiland SK, Williams HC. International Study of asthma and allergies in childhood (ISAAC): Rational and Methods. Eur Respir J 1995; 8:483-491.. In Brazil, this instrument was translated into Portuguese and both reproducibility and validity have been verified¹³13. Solé D, Vanna AT, Yamada E, Rizzo MC, Naspitz CK. International Study of Asthma and Allergies in Childhood (ISAAC) written questionnaire: validation of the asthma component among Brazilian children. J Investig Allergol Clin Immunol 1998; 8(6):376-382..

Despite advances in data recording aiding the estimates of asthma prevalence in Brazil, regional data are still scarce. To date there has been limited capacity to identify the magnitude of disease burden within specific populations and compare the results with previously obtained data from other regions of the country⁹9. Barreto ML, Ribeiro-Silva RC, Malta DC, Oliveira-Campos M, Andreazzi MA, Cruz AA. Prevalência de sintomas de asma entre escolares do Brasil: Pesquisa Nacional em Saúde do Escolar (PeNSE 2012). Rev Brasileira de Epidemiologia 2014; 17(Supl.1):106-115.. Within this context, the present study utilized ISAAC questionnaires to investigate asthma prevalence and factors related to its development in schoolchildren living in central and peripheral areas of the city of Montes Claros, Minas Gerais.

Methods

A cross-sectional study was performed, carried out in two sequential and dependent stages. Schoolchildren aged from 6 to 14 years old, living in central and peripheral areas of Montes Claros, Minas Gerais, Brazil and who were registered with the Family Health Strategy (FHS) program were eligible to participate in the first stage of the study.

Initially, a standard written questionnaire (WQ) developed by ISAAC was administered in a version validated for use in the Brazilian population¹⁰10. Casagrande RRD, Pastorino AC, Souza RGL, Leone C, Solé D, Jacob CMA. Asthma prevalence and risk factors in schoolchildren of the city of São Paulo, Brazil. Rev Saude Publica 2008; 42(3):517-523.. Between the end of 2007 and the beginning of 2008, 1,240 WQs were distributed, with 1,131 of them being considered valid, as they were answered properly (8.8% loss). These questionnaires were forwarded to parents and/or guardians responsible for the students and were administered during FHS medical meetings or by the research team directly at the recipients’ homes. Questionnaires were collected after a maximum of five days. Written informed consent on behalf of the student was considered an inclusion criterion.

The WQ contains a field requesting a brief description of student personal data and income, in addition to three sections specific to asthma, allergic rhinitis and eczema. With respect to asthma, the evaluated topics were: cumulative prevalence, active asthma condition, medical diagnosis, associated symptoms, severity, and association with other allergic diseases (rhinitis, eczema and rhinitis, or eczema alone ). The prevalence of accumulated asthma was evaluated by the percentage of affirmative answers to question 1 of the asthma module: “wheezes at some point in your life?”. The prevalence of active asthma was estimated by the percentage of affirmative responses to question 2: “wheezes in the last 12 months?”. The prevalence of asthma as diagnosed by a physician was assessed indirectly by affirmative answers to question 6: “asthma any time in life?”. When necessary, the technical terms and any other doubt regarding the questions were explained during the interview.

In accordance with the answers to the WQ, a second stage case control study was performed, where students were divided into asthmatic (A) and non-asthmatic (NA) groups. Students providing positive answers to question 2 of the ISAAC questionnaire, which asked about “the occurrence of wheezes in the last 12 months” were considered asthmatics. Potential factors associated with the occurrence of asthma in the population were investigated, using the complementary questionnaire (CQ) from ISAAC phase II¹⁰10. Casagrande RRD, Pastorino AC, Souza RGL, Leone C, Solé D, Jacob CMA. Asthma prevalence and risk factors in schoolchildren of the city of São Paulo, Brazil. Rev Saude Publica 2008; 42(3):517-523. in both groups. The CQ is comprised of 33 questions related to personal data, environmental, dietary and family conditions, diet, infections and immunizations.

Sampling during the second stage was performed with the purpose of keeping the NA/A ratio close to two to one. A 20% in controls prevalence for each factor associated with asthma , 1.5 odds ratio (OR), alpha error of 5% and test power of 85%⁵5. Chong-Neto HJ, Rosário NA, Solé D, Latin American ISAAC Group. Asthma and rhinitis in South America: how different they are from other parts of the world. Allergy Asthma Immunol Res 2012; 4(2):62-67. were assumed. Therefore, all 230 schoolchildren classified as A were included and 460 NA patients were selected by simple random sampling. The final sample, consisting of the selected students whose parents answered the CQ, contained 172 (31.2%) individuals within the A group and 379 (68.8%) within of the NA group. Similarities between the A and NA groups, in terms of distribution of variables such as gender, residential location (peripheral or central area) and maternal education, was confirmed using chi-square tests. P-values < 0.05 were considered significant.

The study also included a skin test for immediate hypersensitivity (STIH) and a parasitological stool test (PST). The STIH included a standard battery of aeroallergens (FDA Allergenic®, Brazil): Dermatophagoides pteronyssinus (Dp), Blomia tropicalis (Bt), German cockroach (Gc), American cockroach (Ap), dog epithelium (De), cat epithelium (Ce), pollen mix (Po), fungi mix (Fa), positive control (histamine, 10 mg/mL) and negative control (excipient, salt solution). The test was performed on the anterior surface of the forearm and allergens that induced papule formation with an average diameter equal to or greater than 3 mm were considered positive¹⁴14. Oppenheimer J, Nelson HS. Skin testing. Ann Allergy Asthma Immunol 2006; 96(2 Supl. 1):6-12..

The initial parasitological test was carried out by processing the students stool samples using the Hoffmann spontaneous sedimentation technique¹⁵15. Farthing MJ. Parasitic and fungal infections. In: Walker WA, Durie PR, Hamilton JR, Walker-Smith JA, Watkins JB, organizadores. Pediatric gastrointestinal disease: pathophysiology, diagnosis, management. 3a ed. Ontario: BD Decker; 2000. p. 512-521.. The students who tested positive for larvae or eggs of the following helminths were considered to have a parasitic infection: Strongyloides stercoralis, Ascaris lumbricoides, Ancylostoma duodenale, Necator americanus, Taenia solium and Schistosoma mansoni.

Obtained data were entered into an Excel® spreadsheet and statistical analysis was conducted with SPSS® software (Inc, Chicago, IL). The relative and absolute frequencies of studied variables were determined. The association between asthma prevalence and independent variables (personal characteristics, environmental characteristics, eating habits, and health conditions) were tested by bivariate analysis and multivariate analysis using non-conditional binary logistic regression, with estimated OR and respective 95% confidence intervals (CI 95%) reported. Only variables having p-values < 0.20 in bivariate analysis were included in multivariate analysis, and were assessed using the stepwise backward selection procedure. The final model was comprised of factors associated with asthma occurrence (at 5% level) and/or those kept as control variables. The Hosmer-Lemeshow test was used to determine the quality of the model fit to the observed data¹⁶16. Hosmer DW, Lemeshow S. Applied logistic regression. 2a ed. New York: John Wiley & Sons Inc; 2000..

The study was approved by the Ethics Committees of both São Paulo Federal University and Montes Claros State University. All parents and/or guardians provided written informed consent.

Results

The prevalence of asthma, rhinitis and eczema symptoms within the group of 1,131 students answering the WQ during the first stage of the study were assessed according to residential location (center or periphery) and are shown in Table 1. The prevalence of asthma based on symptoms and medical diagnosis, as well as the prevalence of flexural eczema was higher among students from peripheral areas, while cases of rhinitis mainly occurred in individuals from the central area (Table 1).

Of the 551 students participating in the second stage of the study, 48.8% were male and 51.2% female, 46.6% lived in peripheral areas and 53.4% in the central city area. Table 2 shows the results of bivariate analysis assessing relationships between personal, environmental, eating and health characteristic of evaluated schoolchildren based on the presence or absence of asthma. Variables with p-values below 0.20 were chosen for integration into the multivariate model.

In the multivariate analysis (Table 3), attendance at kindergarten (OR = 1.67), household smoking (OR = 1.53), occurrence of rhinitis (OR = 3.35), family history of asthma (OR = 3.02) and positive STIH (OR = 2.48) remained significantly associated with the prevalence of asthma.

Discussion

The development of asthma is multifactorial in nature and is associated with both genetic and phenotypic heterogeneity, making it challenging to compare the results from different asthma studies¹⁷17. Bernd LAG, Di Gesu GMS, Di Gesu RW. Diagnóstico em doenças alérgicas. In: Solé D, Bernd LAG, Filho NAR, organizadores. Tratado de alergia e imunologia clínica. São Paulo: Editora Atheneu; 2011. p. 111-122.. Asthma presents as a complex interaction between environmental stimuli and immunological responses¹⁷17. Bernd LAG, Di Gesu GMS, Di Gesu RW. Diagnóstico em doenças alérgicas. In: Solé D, Bernd LAG, Filho NAR, organizadores. Tratado de alergia e imunologia clínica. São Paulo: Editora Atheneu; 2011. p. 111-122.. In this study, the application of an ISAAC standard questionnaire aided the identification of factors associated with asthma prevalence, including attendance at kindergarten, household smoking, family history and factors linked to the immunological system, such as rhinitis and positive responses to STIH. Although the data were collected in 2007-2008, it should be taken into account that the prevalence of asthma in Brazil has been a significant health problem for many years⁵5. Chong-Neto HJ, Rosário NA, Solé D, Latin American ISAAC Group. Asthma and rhinitis in South America: how different they are from other parts of the world. Allergy Asthma Immunol Res 2012; 4(2):62-67.^,1818. Barros MBA, Francisco PMSB, Zanchetta LM, Cesar CLG. Tendências das desigualdades sociais e demográficas na prevalência de doenças crônicas no Brasil, PNAD: 2003- 2008. Cien Saude Colet 2011; 16(9):3755-3768.^,1919. Moreia MCN, Gomes R, SA MRC. Doenças crônicas em crianças e adolescentes: uma revisão bibliográfica. Cien Saude Colet 2014; 19(7): 2083-2094.. The results from this study are therefore likely to have current relevance. In addition, this work addresses a gap in knowledge regarding asthma epidemiology in Montes Claros, and in future will serve as a reference for the adoption of control measures for asthma in this region.

Epidemiological data shows that children born and raised in rural environments are exposed to a wider diversity of microorganisms such as fungi and bacteria. This results in the development of stronger innate and adaptive immunity, including increased activity of regulatory T cells, which act as mediators of such protection²⁰20. Fishbein AB, Fuleihan RL. The hygiene hypothesis revisited: does exposure to infectious agents protect us from allergy? Curr Opin Pediatr 2012; 24(1):98-102.^,2121. Jucá SCB, Matos P, Takano AO, Moraes LSL, Guimarães LV. Prevalência e fatores de risco para asma em adolescentes de 13 a 14 anos do Município de Cuiabá, Mato Grosso, Brasil. Cad Saude Publica 2012; 28(4):689-697.. In this study however, children from peripheral areas, who may be comparable to children from rural areas, presented with higher incidence of asthma and eczema. Usually, socioeconomic conditions in these areas, such as poor sanitation, substandard living conditions and large reservoirs of inhalant allergens contribute to disease development²²22. Bacon SL, Bouchard A, Loucks EB, Lavoie KL. Individual-level socioeconomic status is associated with worse asthma morbidity in patients with asthma. Resp Res 2009; 17:125.. Despite the urbanization of rural and remote areas in Brazil and other places in Latin America, with the aid of social and health programs and broadening of infrastructure services²³23. Felizola MLBM, Viegas CAA, Almeida M, Ferreira F, Santos MCA, Martinho CA. Prevalence of bronchial asthma and related symptoms in schoolchildren in the Federal District of Brazil: correlations with socioeconomic levels. Jornal Brasileiro de Pneumologia 2005; 31(6):486-491.^,2424. Cooper PJ, Rodrigues LC, Barreto ML. Influence of poverty and infection on asthma in Latin America. Curr Opin Allergy Clin Immunol 2012; 12(2):171-178., there are still discrepancies in healthcare and disease prevalence, as disclosed by this study.

Kindergarten attendance was a personal characteristic assessed as a possible factor associated with the incidence of asthma in the investigated population. Other studies report that kindergarten attendance may contribute to development of the immune system and, therefore, can act as a protective factor against the development of childhood asthma. It is likely that kindergarten attendance promotes interactions between children of different ages in an environment with a high diversity of microorganisms²⁵25. Ball TM, Castro-Rodriguez JA, Griffith KA, Holberg CJ, Martinez FD, Wright AL. Siblings, day-care attendance, and the risk of asthma and wheezing during childhood. N Eng J Med 2000; 343(8):538-543.. In this study however, the chance of asthma development in children who attended kindergarten was 1.67 times higher compared with those who did not. This suggests that attending kindergarten is not a factor able to solely explain the emergence of childhood asthma. Further investigations will be necessary to ascertain what conditions are associated with the development of asthma in children attending kindergarten.

Among the environmental factors studied, the only factor associated with higher prevalence of asthma was the presence of household smokers, which increased disease prevalence by 1.53-fold. Tobacco smoke is an environmental pollutant of high impact since it is composed of several toxic, carcinogenic and mutagenic substances, which negatively affect the health of both active and passive smokers²⁶26. Boldo E, Medina S, Oberg M, Puklová V, Mekel O, Patja K, Dalbokova D, Krzyzanowski M, Posada M. Health impact assessment of environmental tobacco smoke in European children: sudden infant death syndrome and asthma episodes. Public Health Rep 2010; 125(3):478-487.. There are controversies regarding the association of age with vulnerability to tobacco smoke, however some studies indicate that maternal or familial smoking causes the development and/or exacerbation of asthma¹⁰10. Casagrande RRD, Pastorino AC, Souza RGL, Leone C, Solé D, Jacob CMA. Asthma prevalence and risk factors in schoolchildren of the city of São Paulo, Brazil. Rev Saude Publica 2008; 42(3):517-523.^,2727. Menzies D. The case for a worldwide ban on smoking in public places. Curr Opin Pulm Med 2011; 17(2):116-122.. In the pre and postnatal phases, it is known that tobacco smoke leads to the development of asthma through induction of interleukin (IL)-13, which stimulates immunoglobulin E (IgE) production, infiltration of inflammatory cells and bronchial hyper-reactivity²⁷27. Menzies D. The case for a worldwide ban on smoking in public places. Curr Opin Pulm Med 2011; 17(2):116-122.. This knowledge reinforces the necessity of compliance with the World Health Organization recommendations to utilize legislation and public education to ensure completely tobacco free environments. Such actions would assist in reducing the negative impact of smoking on children’s and young people’s health²⁶26. Boldo E, Medina S, Oberg M, Puklová V, Mekel O, Patja K, Dalbokova D, Krzyzanowski M, Posada M. Health impact assessment of environmental tobacco smoke in European children: sudden infant death syndrome and asthma episodes. Public Health Rep 2010; 125(3):478-487..

The development of asthma is frequently associated with atopic sensitization, which can also contribute to rhinitis and eczema development²⁸28. Kurzius-Spencer M, Guerra S, Sherrill DL, Halonen M, Elston RC, Martinez FD. Familial aggregation of allergen-specific sensitization and asthma. Pediatr Allergy Immunol 2012; 23(1):21-27.. In this study, asthma was positively associated with the occurrence of allergic rhinitis, as previously reported in other epidemiological studies²⁹29. Ciprandi G, Cirillo I, Signori A. Impact of allergic rhinitis on bronchi: an 8-year follow-up study. Am J Rhinol Allergy 2011; 25(2):72-76.^,3030. Solé D, Camelo-Nunes IC, Wandalsen GF, Rosário NA, Sarinho EC, Brazilian ISAAC Group. Is allergic rhinitis a trivial disease? Clinics 2011; 66(9):1573-1577.. In our work, prevalence of allergic rhinitis increased the chance of asthma development by 3.35-fold, which is consistent with previous literature³¹31. Lasmar LMLBF, Camargos PAM, Ordones AB, Gaspar GR, Campos EG, Ribeiro GA. Prevalence of allergic rhinitis and its impact on the use of emergency care services in a group of children and adolescents with moderate to severe persistent asthma. Jornal de Pediatria 2007; 83(6):555-561.. Furthermore, the chance of asthma development was 2.48 times higher in children with positive STIH results, which is the most popular method for the diagnosis of allergic diseases, particularly those caused by aeroallergens¹⁷17. Bernd LAG, Di Gesu GMS, Di Gesu RW. Diagnóstico em doenças alérgicas. In: Solé D, Bernd LAG, Filho NAR, organizadores. Tratado de alergia e imunologia clínica. São Paulo: Editora Atheneu; 2011. p. 111-122.^,3232. Bousquet J, Heinzerling L, Bachert C, Papadopoulos NG, Bousquet PJ, Burney PG, Canonica GW, Carlsen KH, Cox L, Haahtela T, Lodrup Carlsen KC, Price D, Samolinski B, Simons FE, Wickman M, Annesi-Maesano I, Baena-Cagnani CE, Bergmann KC, Bindslev-Jensen C, Casale TB, Chiriac A, Cruz AA, Dubakiene R, Durham SR, Fokkens WJ, Gerth-van-Wijk R, Kalayci O, Kowalski ML, Mari A, Mullol J, Nazamova-Baranova L, O’Hehir RE, Ohta K, Panzner P, Passalacqua G, Ring J, Rogala B, Romano A, Ryan D, Schmid-Grendelmeier P, Todo-Bom A, Valenta R, Woehrl S, Yusuf OM, Zuberbier T, Demoly P, Global Allergy and Asthma European Network, Allergic Rhinitis and its Impact on Asthma. Practical guide to skin prick tests in allergy to aeroallergens. Allergy 2012; 67(1):18-24..

Allergies occur most frequently after children reach the age of two years²⁸28. Kurzius-Spencer M, Guerra S, Sherrill DL, Halonen M, Elston RC, Martinez FD. Familial aggregation of allergen-specific sensitization and asthma. Pediatr Allergy Immunol 2012; 23(1):21-27.. Among the major sensitizing agents are mites within house dust, fungi, cockroaches and animal epithelial allergens²⁸28. Kurzius-Spencer M, Guerra S, Sherrill DL, Halonen M, Elston RC, Martinez FD. Familial aggregation of allergen-specific sensitization and asthma. Pediatr Allergy Immunol 2012; 23(1):21-27.. Such agents, as well as the immunological responses they initiate, are important risk factors for asthma development, and sensitized children have higher chances of developing new or more severe allergic conditions when constantly exposed to specific allergens³³33. Solé D, Cassol VE, Silva AR, Teche SP, Rizzato TM, Bandim LC, Sarinho ES, Camelo-Nunes IC. Prevalence of symptoms of asthma, rhinitis and atopic eczema among adolescents living in urban and rural areas in different regions of Brazil. Allergol Immunopathol (Madr) 2007; 35(6):248-253..

Genetic factors may also be related to asthma, since the prevalence of allergy in relatives, especially first-degree relatives, is considered an important risk factor for asthma development³⁴34. Lugogo N, Kraft M. Epidemiology of asthma. Clinics in Chest Medicine 2007; 27(1):1-15.. Confirming this , our results showed that children whose parents, particularly mothers, reported asthma, rhinitis or eczema had a 3.02 times higher chance of developing asthma. However, genetic factors alone cannot explain the prevalence of asthma, and the involvement of geographic and environmental factors should be considered⁶6. Thomsen SF, Duffy DL, Ohm KK, Backer V. Genetic influence on the age at onset of asthma: a twin study. J Allergy Clin Immunol 2010; 126:626-630.^,3535. Kuriakose JS, Miller RL. Environmental epigenetics and allergic diseases: recent advances. Clin Exp Allergy 2010; 40(11):1602-1610.. Therefore, the higher association of maternal allergies with asthma development may also involve immunologic factors during pregnancy, genetic polymorphisms, interactions with oxidative stress genes, maternal exposure to environmental factors both inside and outside the home, exposure to tobacco smoke and occurrence of maternal atopy¹¹11. Sly PD. The early origins of asthma: who is really at risk? Curr Opin Allergy Clin Immunol 2011; 11(1):24-28.^,3636. Yang KD, Ou CY, Hsu TY, Chang JC, Chuang H, Liu CA, Liang HM, Kuo HC, Chen RF, Huang EY. Interaction of maternal atopy, CTLA-4 gene polymorphism and gender on antenatal immunoglobulin E production. Clin Exp Allergy 2007; 37(5):680-687..

In conclusion, asthma prevalence in schoolchildren in Montes Claros was not only related to genetic predisposition, but was also associated with individual history, social demographics, exposure to pollutants such as tobacco smoke and positive responses to allergens. These results obtained can be compared to those from other studies, since they were obtained using a standardized ISAAC protocol. A limitation to this study was the cross-sectional design, limiting our ability to identify the time sequences between exposure to risk factors and development of allergic diseases. However, the data are useful for highlighting the role of residential location in increasing the risk of asthma development, and demonstrate a need for planning specific strategies to prevent and control asthma.

Acknowledgements

We would like to acknowledge Cristiane Silva, for tirelessly organizing the agenda, contacts and materials for this study, the Montes Claros ESF teams, students of the Unimontes and Funorte medicine courses and the students participating in the study. The study was financed by FAPESP.

References

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