Systemwide Evaluation of Field Medicine Programs in Los Angeles County: Protocol for a Mixed Methods Longitudinal...

People experiencing homelessness face high morbidity and unmet health care needs. To address these gaps, health care providers across the United States are increasingly adopting "field medicine" models that deliver mobile health services in shelters, homeless encampments, mobile clinics, and other community settings. Despite their expanding use, systematic evaluations of field medicine programs remain limited.

This paper aims to describe a protocol for a mixed methods evaluation of field medicine for people experiencing homelessness across Los Angeles (LA) County, California.

People experiencing homelessness receiving field medicine were recruited into an ongoing longitudinal study of LA County's unhoused population; a subset of participants in the existing probability-sampled cohort serves as the comparison group. Using monthly online survey data and a quasi-experimental design, we examine who accesses field medicine, how patients use and perceive care, and the impact of field medicine on health and service engagement. We also conduct participant observation of field medicine teams to document patient-provider interactions, care coordination, and carry out semistructured interviews with providers, patients, and nonpatients. Quantitative survey and qualitative findings will be integrated to identify convergence, complementarity, and explanatory insights.

Recruitment of people experiencing homelessness receiving field medicine occurred between August 2024 and October 2025. Among 847 individuals referred from field medicine, 749 (88.4%) were eligible, and 436 (51.5%) completed the first monthly survey and were enrolled. For the comparison group, 902 (63.8%) of the 1413 participants ever enrolled in the existing cohort completed a survey during the field medicine recruitment period and met eligibility criteria. Participant observation included 82 field visits (≈500 h) across diverse service locations and more than 300 patient-clinician interactions. Semistructured interviews were conducted with 15 (30%) providers, 23 (46%) field medicine patients, and 12 (24%) nonpatients.

This study represents one of the first large-scale mixed methods evaluations of field medicine. With increasing health threats from criminalization, climate-related events, and other socioenvironmental hazards, field medicine may mitigate health risks and improve systems engagement for people experiencing homelessness. Findings will provide rigorous evidence to inform service delivery and policy decisions.