Surveillance/Surveys Self-reported asthma symptoms in children and adults of Bangladesh: findings of the National Asthma Prevalence Study M Hassan et al. Int J Epidemiol 2002;31: Fushun Zhang Zubin Punthakee Peter Ghali Yejun Xu Michael Zappitelli

Overview Recent international studies of the prevalence and characteristics of asthma European Commission Respiratory Health Study International Study of Asthma and Allergies in Childhood No population studies to assess the magnitude of asthma in Bangladesh

Study Questions What is the prevalence of asthma in adults and children in Bangladesh in 1999? What are the factors associated with asthma in Bangladesh?

Population and Sample Entire population of Bangladesh > 5 y/o Sampling method: –multistage stratified random sample 64 districts 4 metropolitan cities6 district towns6 rural districts 14 city blocks12 city blocks12 villages x xx 25 households34 households xxx All members

Appropriate Design? Yes Population based prevalence study –stratified random sampling to be representative –cross-sectional survey

Appropriate Sampling Frame? Not described –census, phone book, trial & error Households –doesn’t include homeless which make up a large part of the Bangladeshi population

Adequate Sample Size? No sample size calculation Estimated prevalence 11.8% Acceptable margin of error 2% n=(1.96/0.02) 2 x 0.118( ) = 1000 * Their n = 5642 * for independent sample

Acceptable outcome measurement? “Pretested structured questionnaire” face-to-face interview with housewife (modified from ECRHS & ISAAC) Objective - No self-report of wheeze, night cough, perceived asthma, diagnosed asthma by a doctor or “quack” Suitable - Yes given population-based, various education levels Standard - No modified from a European questionnaire without description of “pre-testing” they did provide operational definitions

Unbiased outcome measurement? No Social desirability (perceived secondary gain) Recall bias Observer bias No blinding of observer to risk factors

Response rate? Nonresponders? Response rate not described but calculated: –963 / 1166 households (83%) Non-reponders were not described, or even mentioned. This may introduce selection bias.

Prevalence estimates with CIs? Recent wheeze 6.9% { } –Metropolitan 6.6% { } –other urban 7.8% { } –rural areas 7.0% { } By age, economic status, education, household size, odds ratios {95% CI} were reported

Implications of the study Asthma prevalence is lower in Bangladesh than more industrialized countries Prevalence is higher in younger, more educated, high socioeconomic status, smaller households May suggest a need to –target interventions at more advantaged, or –improve detection in the disadvantaged Generates hypotheses: eg. Dirtier environments protect against asthma