Neighborhood Disparities in Interstitial Lung Disease: How Do We Capture the Most Vulnerable?

Neighborhood disadvantage is an important predictor of clinical outcomes in patients with fibrotic interstitial lung disease (fILD) (1, 2), but until now, we have not known the components of this complex socioeconomic indicator that contribute the most harm to this vulnerable population. In this issue of AnnalsATS, DeDent and colleagues (pp. 402–410) tackle this critical question by applying the California Healthy Places Index (HPI) to patients with idiopathic pulmonary fibrosis (IPF) enrolled in the University of California, San Francisco (UCSF) ILD Registry (3, 4). This novel study highlights how economic factors and impaired access to care underlie the disparate outcomes seen in patients with IPF who live in more disadvantaged neighborhoods. Such work is essential to identifying avenues through which legislative, regulatory, and policy interventions can be focused to mitigate these disparities.

This was a single-center study of 783 patients with IPF from UCSF, with most patients residing in or near San Francisco, an area renowned for being one of the most expensive places to live in the United States (5). Using a methodological approach similar to those of prior studies of disadvantage in patients with fILD (1, 2), DeDent and colleagues demonstrate that higher neighborhood advantage is associated with higher baseline forced vital capacity (FVC) and diffusing capacity of the lung for carbon monoxide (Dl_CO). Most domains of the HPI influenced both lung function outcomes, with the economic and access domains demonstrating the largest effect estimates. The authors comment that this finding is distinct from our group’s prior work that did not demonstrate any significant influence of neighborhood disadvantage on baseline FVC and Dl_CO in a subgroup of patients with IPF (1). Although this is correct, our prior work did demonstrate in the full cohort of patients with diverse forms of fILD that higher disadvantage in both Canadian and U.S. cohorts was associated with lower baseline Dl_CO, indicating that neighborhood disadvantage impacts on initial access to tertiary ILD care may transcend borders and healthcare systems.

Surprisingly, a composite pollution domain of the HPI did not influence baseline lung function in this study, a finding that contrasts with other studies of pollution impacts on lung function in fILD (6, 7). This lack of association must be interpreted with caution, given the nonspecific nature of the pollution domain within HPI, which reflects multiple pollutants simultaneously and is temporally insensitive.

In contrast to our prior findings in which greater neighborhood disadvantage was associated with increased mortality in U.S. patients with IPF (1), DeDent and colleagues did not find an association of HPI with mortality in their full cohort. In subgroup analysis evaluating mortality in patients with higher baseline lung function, however, an effect of disadvantage on mortality was unmasked such that patients with normal or only mildly impaired FVC (i.e., ⩾70% predicted) had a hazard ratio for mortality of 1.82 (95% confidence interval, 1.21–2.74; P = 0.004). They also found in models that did not adjust for baseline FVC or Dl_CO, but adjusted for other relevant covariates, that greater disadvantage was significantly associated with increased mortality, indicating that disadvantage-induced mortality impacts are at least in part mediated through lung function. Overall, DeDent and colleagues’ mortality findings suggest that once patients reach a more severe state of disease, as indicated by lower lung function, IPF progresses with a more immutable trajectory. In contrast, early disease identification may present opportunities to mitigate socioeconomic and access-based disadvantage and to initiate early therapeutic interventions to improve prognoses in our most vulnerable patients. It is critical that we develop an approach for earlier identification of patients with IPF, especially for individuals who live in areas with greater disadvantage, whose progressed state of disease at diagnosis indicates delays in their access to tertiary ILD care.

Beyond delays in subspecialty access, it appears that we are failing to capture many of the most disadvantaged individuals in our ILD registries. We previously demonstrated that our University of Pittsburgh cohort had reduced representation of individuals in the most disadvantaged groups as compared with national and statewide populations (1). This skewed distribution of neighborhood disadvantage is even further pronounced in the present study, where patients are generally recruited to the UCSF cohort from the highly affluent Bay Area of California. DeDent and colleagues acknowledge this limitation and provide information regarding the distribution of their cohort’s disadvantage score against the California HPI distribution, highlighting how their cohort is lacking in patients from the most disadvantaged segments of society. This fact is even more stark when looking at the U.S.-wide Area Deprivation Index (ADI) (8). The ADI is a measure of material and social neighborhood disadvantage previously studied in fILD, which ranges from 0 to 100, with 0 reflecting the least and 100 the most disadvantage. The median ADI score in the DeDent and colleagues study is 12, whereas the U.S. population median sits at 50 (Figure 1A). As such, the UCSF cohort reflects a highly advantaged group in comparison with the total U.S. population. Consequently, it is reasonable to suspect that even more robust impacts of neighborhood disadvantage on lung function and mortality would be identified in a U.S. population–based cohort that equitably captured all individuals with IPF. The present study by DeDent and colleagues underscores the necessity for us to identify and provide care for patients with fILD from these most underserved groups. Further work is also needed to determine whether individuals with greater neighborhood disparities are more likely to develop fILDs, as seems likely, given our understanding of social determinants of health and the existing evidence that environmental factors such as air pollution which are correlated with neighborhood disadvantage (9) also contribute to IPF incidence (10, 11).

Figure 1.

(A) Reproduction of Figure E4 from the data supplement of DeDent and colleagues demonstrates the Area Deprivation Index (ADI) score for all patients with idiopathic pulmonary fibrosis (IPF) included in the University of California, San Francisco (UCSF) cohort. Superimposed on the plot with vertical black dashed lines are the UCSF cohort median ADI and the U.S. nationwide median ADI. The horizontal red dashed line reflects the proportion that each bar in the histogram should reflect if the cohort population perfectly matched the entire U.S. population, and, based on this estimate, the red shading reflects the proportion of more disadvantaged patients with IPF who are likely missing from this cohort. (B) The natural history of IPF from prediagnosis to end of life, highlighting barriers to care that likely contribute to disparities in patients with ILD and potential future mitigation strategies. Figure made with Biorender. References 11–20 are cited in the figure text. CT = computed tomography; ILD = interstitial lung disease; PFT = pulmonary function testing.

To mitigate the harms of neighborhood disparities in patients with fILD, it is critical for us first to understand how these complex social determinants influence the life course of our patients. Figure 1B demonstrates the pathways through which neighborhood disadvantage may contribute to fILD development and progression, also highlighting opportunities to lessen these disparities (10, 12–20). Clinicians and scientists have a duty to advocate for policies, regulations, and systems that provide equitable access to all patients, regardless of race, sex, income, or other discriminating factors. We can do this through participating in community advocacy organizations, petitioning our legislators to increase healthcare and insurance access for low-income and minoritized individuals, investing in social policies that mitigate poverty, dismantling systemic racism and discrimination in health care, and increasing the accessibility of tertiary ILD centers, potentially through the increased dissemination of telehealth resources. It is within the duties of clinicians to advocate for health equity, especially given the increasing body of evidence underscoring the complex social, demographic, and environmental factors that contribute to the development and progression of IPF and other fILDs. The present work by DeDent and colleagues should stand as a call to action for ILD clinicians to implore our healthcare systems, regulators, and legislators to facilitate improved access to tertiary ILD care, because it is clear we are only capturing the tip of the iceberg of these devastating diseases.