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.

Mobile health units (MHUs) can reach populations facing barriers to traditional primary care, but information about factors associated with their utilization is limited. The objective of this ecological study was to evaluate whether MHU encounter density is increased in census tracts designated as Primary Care Health Professional Shortage Areas (HPSAs) and explore whether associations varied by socioeconomic vulnerability. We analyzed Wayne State University/Wayne Health MHU encounters with adult patients from July 2021 to September 2025. Negative binomial regression models with a log link and log(population) offset tested the a priori hypothesis that encounter density was increased in designated versus undesignated HPSA census tracts. Sensitivity analyses assessed variation by social 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. Overall, 13,852 encounters with 10,924 unique patients occurred across 924 of 1305 census tracts. Encounter rate per adult population was significantly increased by severalfold comparing designated versus undesignated shortage areas, with stronger associations at lower socioeconomic vulnerability index score quartiles (interaction p = 0.0006). These findings support continued efforts to scale and evaluate MHUs to address projected healthcare shortages, particularly in socioeconomically vulnerable areas.