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

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.