Geographic Barriers to Subspecialty Care Access for Patients With Primary Immune Disorders in the United States

Primary immune disorders, also known as inborn errors of immunity, are associated with substantial diagnostic delays and limited access to rural subspecialty and infusion care. This study measures disparities in access to expert clinical immunologists (ECIs) or infusion centers (ICs) relative to primary care resources in the United States.

To evaluate geographic access quantitatively to ECIs, ICs, and federally qualified health centers (FQHCs) across rural and nonrural regions of the United States.

We analyzed publicly available national datasets. Expert clinical immunologists and FQHCs were identified nationally whereas ICs were evaluated in six states and territories. Rurality was characterized using Rural-Urban Commuting Area (RUCA) codes and population density. Chi-square test with post hoc adjusted Pearson residuals (r) assessed associations between facility type and rurality nationally and within the six-state and territory sample. Geographic information system mapping visualized facilities and 2-hour service radii for ECIs.

Federally qualified health centers were overrepresented in rural regions, comprising approximately 30% of US FQHCs despite only 20% of the population residing rurally. In contrast, ECIs were underrepresented nationally in rural spaces, and both ECIs and ICs were rurally underrepresented in the six-state and territory sample (ECIs RUCA: r = -2.68; ICs RUCA: r = -2.91). Geographic information system mapping revealed rural ECI coverage in only six states. Findings were consistent across rurality definitions, with RUCA codes demonstrating a balanced characterization of rurality.

Rural patients with primary immune disorders, or inborn errors of immunity, face substantial geographic barriers to diagnostic and therapeutic care despite adequate distribution of primary care. Targeted efforts to improve rural subspecialty access are urgently needed.