Epidemiology and risk factors of asthma-chronic obstructive pulmonary disease overlap in low- and middle-income countries

Abstract

Background: Asthma-chronic obstructive pulmonary disease (COPD) overlap (ACO) represents the confluence of bronchial airway hyperreactivity and chronic airflow limitation and has been described as leading to worse lung function and quality of life than found with either singular disease process.

Objective: We aimed to describe the prevalence and risk factors for ACO among adults across 6 low- and middle-income countries (LMICs).

Methods: We compiled cross-sectional data for 11,923 participants aged 35 to 92 years from 4 population-based studies in 12 settings. We defined COPD as postbronchodilator FEV₁/forced vital capacity ratio below the lower limit of normal, asthma as wheeze or medication use in 12 months or self-reported physician diagnosis, and ACO as having both.

Results: The prevalence of ACO was 3.8% (0% in rural Puno, Peru, to 7.8% in Matlab, Bangladesh). The odds of having ACO were higher with household exposure to biomass fuel smoke (odds ratio [OR], 1.48; 95% CI, 0.98-2.23), smoking tobacco (OR, 1.28 per 10 pack-years; 95% CI, 1.22-1.34), and having primary or less education (OR, 1.35; 95% CI, 1.07-1.70) as compared to nonobstructed nonasthma individuals. ACO was associated with severe obstruction (FEV₁ %, <50; 31.6% of ACO vs 10.9% of COPD alone) and severe spirometric deficits compared with participants with asthma (-1.61 z scores FEV₁; 95% CI, -1.48 to -1.75) or COPD alone (-0.94 z scores; 95% CI, -0.78 to -1.10).

Conclusions: ACO may be as prevalent and more severe in LMICs than has been reported in high-income settings. Exposure to biomass fuel smoke may be an overlooked risk factor, and we favor diagnostic criteria for ACO that include environmental exposures common to LMICs.

Keywords: ACO; Asthma; COPD; asthma-COPD overlap; chronic obstructive pulmonary disease; epidemiology; health outcomes; overlap; population-based; risk factors; spirometry.

FIG 1.

Health status by site. Because ACO is defined in this analysis as a combination of fulfilling the criteria for both asthma and COPD, categories are not discrete; an individual may fall into only 1 category. The prevalence of asthma and COPD as separate conditions (along with ACO) can be found in Table E2.

FIG 2.

Forest plot of risk factors for ACO. Risk factors are presented as ORs for presence of ACO compared with reference populations represented by each panel (ACO vs COPD-Only, ACO vs Asthma-Only, ACO vs Nonobstructed nonasthma, and ACO vs all without ACO). ORs are represented by black diamonds while the 95% CI is represented by horizontal bars. Site-specific estimates are represented by gray triangles directly under the overall estimate. Overall estimates were generated via alternating logistic regressions, which accounted for clustering by site. All models included each risk factor presented here.

FIG 3.

Box plots of prebronchodilator and postbronchodilator spirometry z scores by disease status. The top and bottom of the box represent the 75th and 25th percentile values of the distribution, respectively, while the center line represents the median. The circles on the top and bottom represent outlying values. Z scores were calculated on the basis of Global Lung Function Initiative mixed-ethnic reference population and are presented here unadjusted. FVC refers to the maximum total volume of air exhaled. FEV₁/FVC refers to their ratio. FEV₁ and FVC may come from different qualifying spirometry trials.