I congratulate the authors on their article "Prevalence of bronchial asthma and related symptoms in schoolchildren in the Federal District of Brazil: correlations with socioeconomic levels" which enriches the knowledge of the epidemiology of asthma in Brazil.(1)

I would like to make a few comments regarding the article. First, despite the fact that the sampling was probabilistic and the sample was apparently representative, the substitution of incomplete questionnaires with those from other students from the same schools could have created a selection bias, creating a sample consisting of participants that were more interested in filling out the questionnaires, whether because they were more well educated or because they were asthmatic.

Second, the interaction between asthma and socioeconomic condition, as seen for other risk factors, appears in a multicausal form, and the association found in this study was not corrected for confounding factors.

Third, the authors apparently made a mistake when citing our study of asthma prevalence in Recife, stating that we had found an association between greater asthma prevalence and lower level of maternal education. What we found was in fact the opposite, that greater asthma prevalence was associated with a higher level of maternal education.(2) This is in agreement with the observations made by Chew et al.(3) in Singapore using the International Study of Asthma and Allergies in Childhood protocol. Wandalsen,(4) studying school children in the south-central region of the city of São Paulo, found no association between asthma symptoms and maternal schooling, a finding echoed by Moraes et al.(5) in a case control study conducted in Cuiabá.

According to the hygiene theory, children exposed to unhygienic conditions at an early age would be less prone to develop asthma.(6) If that theory holds true, the prevalence of asthma should be lower in the poorest communities.

The final aspect that must be taken into consideration is how we define poverty. According to the Brazilian Institute of Geography and Statistics,(7) poverty is defined as per capita income below the minimum wage. In the study conducted by Filizola et al.,(1) this criterion is not used to define socioeconomic condition. It is therefore likely that the cut-off point was higher.

From my point of view, poverty as a risk factor for asthma is complex and varies from region to region, in Brazil and in the rest of the world. In order to understand this relationship more clearly, case-control and cohort studies are needed.

REFERENCES

1. Felizola MLBM, Viegas CAA, Almeida M, Ferreira F, Santos MCA. Prevalência de asma brônquica e de sintomas a ela relacionados em escolares do Distrito Federal e sua relação com o nível sócioeconômico. J Bras Pneumol. 2006;31(6):486-91.
2. Britto MC, Bezerra PG, Brito RC, Rego JC, Burity EF, Alves JG. Asma em escolares do Recife - comparação de prevalências: 1994-95 e 2002. J Pediatr (Rio J). 2004;80(5):391-400.
3. Chew FT, Goh DYT, Lee BW. Under-recognition of childhood asthma in Singapore: evidence from a questionnaire survey. Ann Trop Paed. 1999;19:83-91.
4. Wandalsen G. Prevalência e fatores de risco para asma e doenças alérgicas em escolares da região centro-sul do município de São Paulo. São Paulo [dissertação]. São Paulo: Universidade Federal de São Paulo; 2003.
5. Moraes LSL, Barros MD, Takano AO, Assami NMC, Fatores de risco, aspectos clínicos e laboratoriaisda asma em crianças J Pediatr (Rio J) 2001; 77 (6): 447-54.
6. Prescott SL, Macaubas C, Smallacombe T, Holt BJ, Sly PD, Holt, PG. Development of allergen-especific T-cell memory in atopic and normal children, Lancet, 1999;353:196-200.
7. IBGE. Estatísticas de pobreza. Disponível em: www.ibge.gov.br/ibgteen/glossario/pobreza.html [2005 ago 23]


Murilo Carlos Amorim de Britto
Professor Fernando Figueira, Instituto Materno Infantil (IMIP, Mother and Child Institute), Recife, Brazil
1. PhD in Public Health, Professor at the Instituto Materno Infantil (IMIP, Mother and Child Institute), Recife, Brazil