Socioeconomic status and COPD among low- and middle-income countries

Abstract

Background: Socioeconomic status (SES) is a strong social determinant of health. There remains a limited understanding of the association between SES and COPD prevalence among low- and middle-income countries where the majority of COPD-related morbidity and mortality occurs. We examined the association between SES and COPD prevalence using data collected in Argentina, Bangladesh, Chile, Peru, and Uruguay.

Methods: We compiled lung function, demographic, and SES data from three population-based studies for 11,042 participants aged 35-95 years. We used multivariable alternating logistic regressions to study the association between COPD prevalence and SES indicators adjusted for age, sex, self-reported daily smoking, and biomass fuel smoke exposure. Principal component analysis was performed on monthly household income, household size, and education to create a composite SES index.

Results: Overall COPD prevalence was 9.2%, ranging from 1.7% to 15.4% across sites. The adjusted odds ratio of having COPD was lower for people who completed secondary school (odds ratio [OR] =0.73, 95% CI 0.55-0.98) and lower with higher monthly household income (OR =0.96 per category, 95% CI 0.93-0.99). When combining SES factors into a composite index, we found that the odds of having COPD was greater with lower SES (interquartile OR =1.23, 95% CI 1.05-1.43) even after controlling for subject-specific factors and environmental exposures.

Conclusion: In this analysis of multiple population-based studies, lower education, lower household income, and lower composite SES index were associated with COPD. Since household income may be underestimated in population studies, adding household size and education into a composite index may provide a better surrogate for SES.

Keywords: COPD; low- and middle-income country; socioeconomic status.

Figure 1

Prevalence of COPD per city using the lower limit of normal (LLN) method of diagnosis with Global Lung Function Initiative (GLI) mixed ethnic population, presented as overall and stratified by sex.

Figure 2

Pre-bronchodilator FEV₁/FVC Z-score using Global Lung Function Initiative (GLI) mixed ethnic population, stratified by age and sex. Notes: Age is stratified into four categories. Males are represented by red box plots and females by green, in ten panels each representing an individual site.

Figure 3

Mean pre-bronchodilator FEV₁ and FEV₁/FVC Z-score using Global Lung Function Initiative (GLI) mixed ethnic population, by elevation in meters and site. Notes: Elevation is in meters on the x-axis with Z-score on the y-axis. City names are beside each corresponding point. The lines represent the fitted values of a regression line of Z-score by elevation.

Figure 4

Odds ratio of COPD by socioeconomic status composite index (SES index), secondary education or higher (below secondary as reference), greater than or equal to median household size of 4 (below as reference), and monthly household income (change per category). Notes: Adjusted odds ratios are displayed for the overall sample (left) and for individual sites (right). In the left panel, the square represents the adjusted odds ratio and the segments represent 95% CIs. In the right panel, the triangles represent site-specific adjusted odds ratios. For the composite SES index, we calculate the interquartile odds ratio of COPD, ie, the ratio of odds of COPD between the 25^th vs 75^th percentile of the composite SES index. Abbreviation: SES, socioeconomic status.

Figure 5

Absolute difference in pre-bronchodilator FEV₁/FVC Z-score by socioeconomic status composite index (SES index), secondary education or higher (below secondary as reference), greater than or equal to household size of 4 (below as reference), and monthly household income (change per category). Notes: We display adjusted differences in pre-bronchodilator FEV₁/FVC Z-score for the overall sample (left) and for individual sites (right). In the left panel, the square represents the adjusted odds ratio and the segments represent 95% CIs. In the right panel, the triangles represent site-specific adjusted odds ratios. For the composite SES index, we calculate the interquartile adjusted difference in pre-bronchodilator FEV₁/FVC Z-score, ie, the difference between the 75th and 25th percentiles of the composite SES index. Abbreviation: SES, socioeconomic status.