Increased Density of Mobile Health Unit Encounters Among Primary Care Health Professional Shortage Areas

Mobile health units (MHUs) offer an attractive means to reach people facing barriers that limit engagement with traditional primary care providers, but evidence on utilization as-sociated factors is sparse. This ecological study leveraged data from Wayne State University/Wayne Health MHU encounters with adult patients from 07/2021-09/2025 to address the knowledge gap. We fit negative binomial regression models with a log link and log(population) offset to test the a priori hypothesis that the density of MHU encounters is increased in designated versus undesignated Primary Care Health Professional Shortage Area census tracts established by the U.S. Health Resources and Services Administration. Sensitivity analyses examined whether the association varied by socioeconomic status vulnerability index score quartiles established by the US Centers for Disease Control and Prevention. One quarter of the five-county metropolitan Detroit, Michigan, catchment area census tracts were designated healthcare shortage areas. There were 13,852 encounters with 10,924 unique patients living in 924 of the total 1,305 census tracts in the catchment. The MHU encounter rate per adult population was significantly increased by severalfold comparing designated versus undesignated healthcare shortage areas; the estimated magnitude of association strengthened with increasing socioeconomic vulnerability index score quartile (interaction p-value, 0.0006). Continued efforts to scale and evaluate the capacity for mobile health units to help address projected healthcare shortages appears warranted, particularly in areas with heightened socioeconomic vulnerability.