The sheer scale of the dataset gives the findings unusual weight. Most research on homeless health relies on cross-sectional surveys or snapshots of emergency department use, which capture a single moment and can exaggerate the role of crisis care. By contrast, the Hamburg team, led by Daniel Tajdar and colleagues at the University Medical Center Hamburg-Eppendorf, mined ten years of continuous clinical records in which healthcare professionals coded every diagnosis according to ICD-10 criteria. That structure allowed the researchers to compute something rarely available for this population: precise odds ratios linking specific diagnoses to two concrete outcomes, referral to specialist outpatient care and referral to hospital.

The demographic profile of the patient population was striking. The mean age was 44.6 years, with a standard deviation of 13.2, and 83.2 percent of the 5,055 patients were male. This is a population that is aging into chronic disease but remains dominated by working-age men, a group that conventional primary care systems in Germany and across Europe frequently fail to reach. Homelessness has increased substantially across Europe in recent years, and it is well established that people experiencing homelessness carry a high burden of disease and face premature mortality. What has been missing, the authors argue, is longitudinal evidence on the actual spectrum of conditions treated and the patterns of referral that follow.

Mental and behavioral disorders emerged as the single most common diagnostic category, recorded in 1,436 patients, or 28.4 percent of the cohort. Within that group, disorders related to psychoactive substance use affected 817 patients, representing 16.2 percent, while alcohol use disorders accounted for 592 patients, or 11.7 percent. These figures quantify what clinicians in homeless services have long observed anecdotally: psychiatric and substance-related conditions are not incidental features of homeless health but its central axis. The concentration of these diagnoses in a relatively young population underscores how mental health and addiction drive the clinical workload long before the chronic diseases of older age take over.

The referral statistics are where the study delivers its most surprising message. Across all 13,330 consultations, only 10.9 percent resulted in any referral at all, split almost evenly between 5.5 percent referred to specialist outpatient care and 5.4 percent referred onward to hospital. In other words, 89.1 percent of consultations ended with the problem managed entirely within the specialized primary care center. For a population often stereotyped as generating constant emergency admissions, the data show that when accessible, low-threshold primary care is available, it functions as a genuine point of care rather than a mere triage station funneling patients toward hospitals.

That said, the conditions that did trigger hospital referral followed a clear and clinically coherent pattern. Alcohol-related disorders were significantly associated with referral to hospital, with an odds ratio of 1.76 and a 95 percent confidence interval of 1.39 to 2.23. Injuries and poisoning, including drug intoxication, also raised the odds of hospital referral, with an odds ratio of 1.64 and a confidence interval of 1.31 to 2.05. Both findings make intuitive sense: acute intoxication, overdose, and traumatic injury are precisely the situations in which primary care settings lack the equipment and staffing to manage patients safely, and rapid transfer to hospital becomes the only responsible option.

The pathway to specialist outpatient care looked different. Referral to specialists was more likely among older patients, with the odds increasing by a factor of 1.34 for every ten-year increase in age, and among patients presenting with musculoskeletal conditions. This gradient suggests that the specialized centers successfully handled the acute and addiction-related presentations that dominate younger patients, while the accumulating chronic burden of older patients, particularly joint, bone, and muscle disorders shaped by years of rough sleeping and physical labor, required specialist input. It is a reminder that as the homeless population ages across Europe, demand for orthopedic and rheumatological care will likely grow even where addiction services are well established.

Methodologically, the study followed the STROBE reporting guidelines for observational research and was approved by the Ethics Committee of the Hamburg Medical Association under file number PV4454. Under German law, specifically paragraph 75 of Book Ten of the Social Code, the evaluation of anonymized routine data is permissible without explicit patient consent, a legal provision that makes studies of this kind feasible without burdening vulnerable patients with research procedures. The work was funded by the Hamburg Social Welfare Authority, though the funder had no role in study design, data collection, analysis, interpretation, or the decision to submit the paper. The authors, spanning the departments of general practice and health services research in Hamburg-Eppendorf, declare no competing interests.

The implications reach well beyond Hamburg. Specialized primary care services for homeless populations exist in various forms across Europe and North America, but evidence about their effectiveness has been thin, and funding often remains precarious. This study provides the strongest longitudinal signal yet that such services can resolve the majority of health problems in-house, reserving hospitals for the acute emergencies that genuinely require them. The authors conclude that strengthening and integrating these services may improve access to care and support continuity of treatment across healthcare settings, a critical point given that fragmented care and lost follow-up are chronic failures in homeless healthcare. Continuity matters doubly here, because the same patients returning over years build the trust that standard clinics often struggle to establish.

The research agenda that follows is equally clear. The authors call for further studies evaluating interventions that specifically target mental health and substance use disorders, which represented the most common health concerns in the cohort. Given that alcohol-related disorders also drove hospital referrals, investments in addiction medicine embedded within homeless primary care could plausibly reduce both suffering and downstream hospital costs. As homelessness continues to rise across European cities, the Hamburg dataset offers a template: ten years of routine clinical data, systematically coded, can transform anecdote into evidence. The message for policymakers is blunt and quantified, with nearly nine out of ten encounters resolved in primary care, the question is no longer whether specialized clinics for people experiencing homelessness work, but how fast they can be scaled.

Subject of Research: Health conditions and healthcare referral patterns among people experiencing homelessness in specialized primary care

Article Title: Health conditions and referral patterns among people experiencing homelessness: a 10-Year longitudinal study of specialized primary care in Hamburg, Germany

Article References: Health conditions and referral patterns among people experiencing homelessness: a 10-Year longitudinal study of specialized primary care in Hamburg, Germany. (n.d.). https://doi.org/10.1186/s12939-026-03071-y

Image Credits: AI Generated

DOI: 10.1186/s12939-026-03071-y

Keywords: homelessness, primary care, hospital referral, mental health, substance use disorders, alcohol-related disorders, ICD-10, longitudinal study, health equity, Hamburg, Germany, health services research