Association of socioeconomic status with respiratory mortality and hospitalisations in COPD: a nationwide cohort study.

BACKGROUND

Socioeconomic status (SES) and air pollution are independently associated with adverse outcomes in patients with chronic obstructive pulmonary disease (COPD). This study investigated the association of SES with respiratory mortality and hospitalisation, while adjusting for air pollution.

METHODS

This retrospective cohort study analysed the individual-level and area-level SES indicators, as well as long-term air pollution exposure, associated with COPD in the Korean National Health Insurance Service-National Sample Cohort. The associations of SES with respiratory mortality and hospitalisation were evaluated using Cox proportional hazards models after adjusting for clinical factors and air pollution.

RESULTS

Among 12 820 patients (mean age: 63.5 years, 47.2% male), 115 (0.9%) and 1870 (14.6%) experienced respiratory mortality and respiratory-related hospitalisation, respectively. Self-employed members had higher mortality risks than self-employed heads (HR=2.397, 95% CI=1.044 to 5.501). Regions with older adults constituting 20-50% of the population exhibited reduced mortality risks (HR=0.516, 95% CI 0.269 to 0.991). The area-level covariates significant in the clinically adjusted models lost significance after adjusting for air pollution. Income level (HR=0.979, 95% CI 0.965 to 0.993) exhibited a negative association with respiratory hospitalisation risks. Suburban (HR=1.321, 95% CI 1.141 to 1.530) and rural (HR=1.398, 95% CI 1.202 to 1.626) residential status was associated with a higher hospitalisation risk. A higher older-adult population was positively associated with hospitalisation risk (HR=1.023, 95% CI 1.014 to 1.033). Higher education level and gross regional domestic product quartiles exhibited reduced hospitalisation risk.

CONCLUSIONS

The associations between SES and mortality and hospitalisation risks remained attenuated and persistent, respectively, after adjusting for air pollution.