Chronic obstructive pulmonary disease (COPD) is a heterogeneous group of slowly progressive diseases characterized by airflow limitation and gradual loss of lung function that is not fully reversible.1 COPD represents 5% of total deaths and is the fourth leading cause of death in the US. The absolute number of deaths from COPD increased 8% from 116,494 in 2000 to 126,005 in 2005.2 During 1980–2000, the overall death rate for COPD increased 67%.3 The COPD average attributable excess health care expenditures are nearly US$6,300 per Medicare patient.4 The annual number of inpatient days for COPD (8.18 days) is only second to chronic kidney disease (9.51 days).5 COPD is highly prevalent and associated with comorbid disease and physical dysfunction.6

Significant sociodemographic disparities in COPD outcomes have been reported for the US. Only a few studies explored their geographic variations.7–10 A broader view of the causes of population health disparities including race, ethnicity, socioeconomic status, and geography is necessary for better solutions to complex population health problems.11 Understanding geographic variations in COPD hospitalization could help public health policy makers more clearly identify target areas with great needs and facilitate the formulation of better solutions to improve COPD prevention and treatment. No previous study has characterized the geographic variations in COPD hospitalization across the US. This study examined geographic disparities in COPD hospitalization of Medicare beneficiaries in the US, at the state and Health Service Area (HSA) level. The geographic variations in regionalized and local environmental factors that contributed to excessive HSA hospitalization risk were then assessed.

Medicare claims data were used to characterize substantial geographic variations in COPD hospitalization risk among states (Figure 1) and HSAs (Figure 2) for individuals aged 65 and older in fee-for-service Medicare. The HSA-level analysis highlights high hospitalization burdens within states whose overall rates may not be high relative to other states. This geographic analysis facilitates identification of target areas of high need, leading to more efficient and effective use of resources. There were distinct geographic patterns in COPD hospitalization risks attributed to regionally-shared environmental risk factors (Figure 3) and HSA-unique environmental contexts (Figure 4). These undefined environmental risk factors for HSA COPD hospitalization are strongly spatially correlated among those neighboring HSAs, while a few HSAs could attribute their COPD hospitalization risk to their unique local environmental context. These findings suggest that two spatial processes may be operating with respect to environmental influences on COPD hospitalization; first, broad regionalized contextual effects (eg, socioeconomic factors and high regionalized population smoking rates) may be exacerbating COPD hospitalizations. Second, localized environmental factors, such as occupational exposures, may be influencing COPD hospitalizations. Further studies are needed to understand these specific regional and local environmental factors contributing to excess or reduced COPD hospitalization risk.

This analysis yields valuable insights into the potential ecological factors that could explain geographic variations in COPD. In turn, this could help to generate hypotheses for further research. For example, the large area of increased hospitalization risk due to regionalized factors (Figure 3) might suggest the inclusion of a socioeconomic status variable such as poverty, as an area-level covariate in further models. In contrast, areas with increased hospitalization risk due to localized factors (for example, many of the HSAs in the western US, shown in Figure 4) might suggest the inclusion of area-level covariates such as the percentage of the population employed in mining or agriculture, in which occupational exposures have been hypothesized to exacerbate COPD, thus leading to higher hospitalization rates.

The drivers of these significant geographic disparities is far from simple, because COPD hospitalization does not only reflect medical care, because also the severity of the COPD and other co-existing chronic conditions.5 There is evidence to suggest that the geographic disparities in COPD hospitalization could be explained mainly by classical risk factors such as smoking, a well-documented individual risk factor for COPD mortality and morbidity.18 However there exists a significant temporal and spatial mismatch between population smoking and COPD hospitalization rates. If smoking is a dominant contributor of COPD hospitalization, one would expect to observe a significant decreasing COPD hospitalization rate in the US. Also, from the geographic perspective, western states (eg, North Dakota, Montana, and Wyoming) have relative high smoking rates19 but low COPD hospitalization rates. Yet, high smoking prevalence is consistent with high COPD hospitalization rates in Appalachian areas and neighboring regions. This geographic match and mismatch between population smoking prevalence and COPD hospitalization rates suggests that environment risk factors may have geographically differential relationships with COPD hospitalization risk. Population smoking could be a major contributor of COPD hospitalization in some areas while other environmental risk factors, such as air pollution (indoor and outside)20–22 and occupational exposures (mining, farming, and construction)23–27 or exposure to biomass heating fuel,20,28,29 could play a dominant role in other areas.

Brown describes significant state-level geographic variations in COPD mortality.7 A state-level comparison between COPD hospitalization and mortality rates shows significant geographic matches and mismatches across the US. This again indicates that these two COPD outcomes share some commonalities in their risk factors but also have differences in their potential sets of risk factors. A further Bayesian spatial mixture model with both COPD outcomes (hospitalization and mortality) at the same time may disentangle the potential factors behind their geographic patterns.

There are a few limitations of this study. First, the study population includes only those individuals age 65 and older who are enrolled in fee-for-service Medicare. It does not include younger individuals or those who are receiving care funded through private savings or other insurance. Having data on these populations would help to better understand COPD hospitalization patterns and factors that could potentially explain geographic variations.

Second, this is an ecological study with potential for ecological fallacy or bias. Observed geographic variations in COPD hospitalization might be a consequence of the different demographic composition in Medicare enrollees. For example, COPD is the third leading cause of mortality for the age group 65–84 and fourth leading cause for the age group of 85 and above.30 Geographic variations in COPD hospitalization should be affected by regional elderly population compositions. However, because Medicare Claims data does not provide accurate measures of individual risk factors, such as smoking and occupation exposure, ecological studies provide a viable framework to evaluate the environmental exposures on COPD hospitalization.

Third, geographic differences in COPD hospitalization may change over time. This study was based on aggregated 12-year Medicare claims data; therefore it was not possible to determine whether the spatial pattern of COPD hospitalization is stable over the study period. Further research is needed to examine the spatiotemporal changes in COPD hospitalization to confirm the implicit assumption of its stable spatial configuration.

COPD is a chronic disease that can be prevented and treated. COPD hospitalization is a costly and sometimes life-threatening event associated with a variety of environmental risk factors, including access to health care.1,31–34 The geographic variation of COPD hospitalization highlights the potential and possibility of reducing its geographic disparities. From population health policy, the observed geographic gaps in COPD hospitalization risk could be the consequence of different regional environmental exposures, but it may be more a result of different COPD community prevention efforts. The variation among states in COPD hospitalization suggests reducing COPD hospitalization burden may be possible on a national scale; although this study did not investigate the exact environmental exposures or community healthcare practices that cause these differences. The differences in COPD hospitalization rates among states and among HSAs further pinpoints the potential local areas which could benefit from enhanced public health efforts to prevent and reduce COPD hospitalization, even among those states with overall lower COPD hospitalization rates. Geographic comparison of lower and higher regional COPD hospitalization risk could also provide insights for better public health practice for COPD prevention. This study focused on the geography of COPD hospitalization burden and risk in order to facilitate public health policy delivery for COPD prevention and to improve public health practice strategies to reduce COPD hospitalization. Future studies could examine the impact of programs such as the National Heart, Lung, and Blood Institute’s (NHLBI) “Learn More Breathe Better” campaign. The NHLBI campaign is focused in the US and seeks to develop better public health policies and strategies in partnership with primary care providers, public health professionals, and persons with or at risk for COPD to reduce the morbidity and mortality burden associated with COPD by increasing awareness and promoting effective prevention and treatment strategies.