Epidemiology and Risk Factors of Asthma-COPD Overlap in Low- and Middle-Income Countries.

BACKGROUND: Asthma-COPD Overlap (ACO) represents the confluence of bronchial airway hyper reactivity 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 six low- and middle-income countries (LMICs).

METHODS: We compiled cross-sectional data for 11,923 participants aged 35-92 years from four population-based studies in 12 settings. We defined COPD as post-bronchodilator FEV1 /FVC 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 (OR=1.48; 95% CI 0.98-2.23), smoking (OR=1.28 per 10 pack-years; 1.22-1.34), and having primary or less education (OR=1.35; 1.07-1.70) compared to non-obstructed individuals. ACO was associated with severe breathing obstruction (FEV1 % predicted <50; 31.5% of ACO vs. 10.9% of COPD alone or 3.5% of asthma alone) and severe spirometric deficits compared to participants with asthma (-1.61 z scores FEV1 ; -1.48, -1.75) or COPD alone (-0.94 z scores; -0.78, -1.10).

CONCLUSION: 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.