Comparing asthma prevalence estimates in Recife

CARTAS AO EDITOR

Comparing asthma prevalence estimates in Recife

Dear Sir,

We would like to comment on a number of methodological issues related to an article by Britto et al.¹ recently published in this journal.

One of the objectives of that study was to evaluate the diagnostic accuracy of the annual prevalence of wheezing as an indicator of asthma. To do this the authors compared answers to two different questions: question 2 (Q2) of the core asthma module of the ISAAC questionnaire - "Have you had wheezing in the past 12 months"? and question 6 (Q6) -"Have you ever had asthma?". It has been previously suggested that, in the absence of a gold standard, results obtained by administering a questionnaire of the signs and symptoms of asthma can be compared to documented diagnosis of asthma made by physicians in the same patients.² In our opinion, information obtained through Q6 cannot be taken as equivalent to a history of physician-diagnosed asthma (clinical examination and diagnosis made by a health professional), since participants' replies to this question will be determined by their own understanding of the term "asthma" rather than by an objective measure of the presence of that disease. Therefore, the reported information seems to merely represent data on the agreement between answers to two separate questions rather than information on the validation of Q2. Validating this question would have required the comparison of replies to Q2 with results from either an objective test (e.g. lung function test), or a clinical examination by a physician, or documented information on a previous diagnosis of asthma from medical records.²

A second methodological issue is concerned with the use of the term cansaço (which in English means feeling breathless or short of breath) as part of the translation of the term "wheeze". Although the ISAAC study group had suggested that asthmatic children and their parents could be asked to describe breathing patterns during an asthma episode,³ we think that the translation of the term "wheeze" as cansaço used in the present study might not be appropriate. First, the term "wheeze" included in the core module of the ISAAC questionnaire corresponds to the terms sibilos, piado or chiado, in Brazilian Portuguese. In contrast, the term cansaço (shortness of breath) has a broader meaning and, in the Brazilian context, it is frequently associated with several clinical conditions other than asthma. Second, the English version of the questionnaire that was used in phase I of the ISAAC only included the terms "wheeze", "cough" and "asthma" (and not "breathless" or "short of breath").⁴ The term "breathless" or "short of breath" was only introduced later in the English version of the phase II ISAAC core questionnaire (module Wheeze and Breathlessness Supplementary Questionnaire).³ It is worth noting that the term cansaço did also not appear in the Brazilian version of the questionnaire designed to be used in Phase I of the ISAAC in Brazil.⁵ Finally, other three English versions of questionnaires designed to study respiratory diseases have used the terms "wheeze", "breathless" and "short of breath" in separate questions or as "shortness of breath with wheezing" (IUATLD, ATS and MRC).² And it has been shown that questions that use the terms "breathless" and "short of breath" have lower specificity in correctly identifying asthma than those using the term "wheeze".²

As a result, by accepting the term cansaço as a translation of "wheeze", Britto et al. may have obtained higher prevalence estimates than surveys based on questionnaires that did not include that term, making the results of the present study less comparable. Moreover, it is unclear whether the term cansaço was used in the survey conducted in 1994-1995⁶ or only in the 2000 survey; if the term was not used, interpretation of the findings from this comparative study will be difficult. In conclusion, we would like to suggest that future surveys of this type use standard questionnaires (e.g. ISAAC) without modification in order to preserve comparability of results across countries and over time. If modifications are judged necessary, they should be incorporated as additional questions, allowing separate analyses, as recommended in textbooks.⁷

Sérgio Souza da Cunha

MD, PhD. Projeto Fatores de risco para Asma e Alergia em Salvador, Instituto de Saúde Coletiva, Universidade Federal da Bahia (UFBA), Salvador, BA

E-mail: [e-mail]

Mar Pujades-Rodríguez

MD, DTM, MSc. School of Community Health Sciences, Nottingham University, United Kingdom

E-mail: [e-mail]

References

1. Britto MC, Bezerra PG, Brito RC, Rego JC, Burity EF, Alves JG. Asma em escolares do Recife - comparação de prevalências: 1994-95 e 2002 (Asthma in schoolchildren from Recife, Brazil, Prevalence comparison: 1994-95 and 2002). J Pediatr (Rio J). 2004;80:391-400.

2. Tennant S, Szuster F. Nationwide monitoring and surveillance question development: Asthma. Working Paper Series No. 2. Public Health Information Development Unit, Adelaide; 2003. Available from: http://www.publichealth.gov.au/

3. ISAAC Study Group [homepage on the Internet]. Auckland: ISAAC Study Group; [updated 2004 Nov 30; cited 2005 Jan 18]. Guidelines for the Translation of Questionnaires; [about 2 screens]. Available from: http://isaac.auckland.ac.nz/PhaseOne/Translation/TransFrame.html

4. Asher MI, Keil U, Anderson HR, Beasley R, Crane J, Martinez F, et al. International Study of Asthma and Allergies in Childhood (ISAAC): rationale and methods. Eur Respir J. 1995;8:483-91.

5. Sole D, Naspitz CK. Epidemiologia da asma: Estudo ISAAC (International Study of Asthma and Allergies in Childhood). Rev Bras Alergia Imunopatol. 1998;21:38-45.

6. Britto MC, Bezerra PG, Ferreira OS, Maranhao IC, Trigueiro GA. Asthma prevalence in schoolchildren in a city in north-east Brazil. Ann Trop Paediatr. 2000;20:95-100.

7. Armstrong BK, White E, Saracci R. The design of questionnaires. In: Armstrong BK, White E, Saracci R. Principles of exposure measurement in epidemiology. Oxford: Oxford University Press; 1992. p. 137-170.

Author's reply

Dear Editor,

Before making any comments about the considerations made by Dr. Cunha and Rodriguez, it should be underscored that the definition of asthma is vague and inaccurate;^1,2 therefore, any observations are subjected to error.

When evaluating the accuracy of wheezing in the past 12 months with the presence of asthma "ever" one should note that the meaning of the term "asthma" varies among different populations, or even between individuals in the same population. According to Dr. Cunha and Dr. Rodriguez, the presence of asthma ever is less accurate than an "objective measure" of the disease. To my knowledge, pulmonary function tests are the only objective measures that are universally accepted for the diagnosis of asthma. According to a systematic review of the literature,³ lung function tests are less accurate than separate questionnaires to determine asthma prevalence. Therefore, unless this scientific evidence is contested with a better one, I believe that even though the presence of asthma ever is not the ideal reference for assessing the accuracy of wheezing in the past 12 months, it is acceptable.

In relation to the use of the terms cansaço or chiado as an equivalent to the English term "wheezing", which literally means only chiado, although we have not tested the validation and reproducibility of the association of these terms, the daily practice with asthmatic children and their families shows that this term is often used by them to mean wheezing. Similarly, in the state of Minas Gerais, it is common to use wheezing for chieira and not for chiado. Therefore, I think the term cansaço, although subjective, can be used in the questionnaires applied in our setting.

Murilo C. A. de Britto

Ph.D., Instituto Materno-Infantil de Pernambuco (IMIP), Recife, PE, Brazil

E-mail: [e-mail]

References

1. National Institute of Health, National Heart, Lung and Blood Institute. Global initiative for asthma. Global strategy for asthma management and prevention. NHLBI/WHO workshop report. Bethesda: National Heart, Lung and Blood Institute. National Institutes of Health, US Department of Health and Human Services; 2002.

2. Warner JO, Naspitz CK, Cropp GJ. Third international pediatric consensus statement on the management of childhood asthma. Pediatr Pulmonol. 1998;25:1-17.

3. Pekkanen J, Pearce N. Defining asthma in epidemiological studies. Eur Respir J. 1999;14:951-7.

6. Britto MC, Bezerra PG, Ferreira OS, Maranhao IC, Trigueiro GA. Asthma prevalence in schoolchildren in a city in north-east Brazil. Ann Trop Paediatr. 2000;20:95-100.

Publication Dates

• Publication in this collection
  23 June 2005
• Date of issue
  Feb 2005