Health care of people experiencing homelessness in the United States

INTRODUCTION — People who experience homelessness have a heavy burden of medical and psychiatric illnesses and use acute health care services at high rates.

This topic presents an overview of homelessness in the United States, discusses common health conditions seen among those experiencing homelessness, and provides recommendations for providing clinical care to this vulnerable population.

The care of specific populations experiencing homelessness can be found in other topics. (See "Palliative care for adults experiencing homelessness" and "Prenatal care for people experiencing homelessness".)

DEFINITION — In 1987, the Stewart B. McKinney Homeless Assistance Act defined a homeless person as someone who lacks a fixed, regular, and adequate nighttime residence and who lives in a shelter or a place not designed for human habitation [1]. In 2009, the Homelessness Emergency Assistance and Rapid Transition to Housing (HEARTH) Act expanded this definition to include people at imminent risk of housing loss within the next two weeks and people fleeing from domestic violence with inadequate resources to obtain other permanent housing [2].

A chronically homeless person is defined by the US Department of Housing and Urban Development (HUD) as an individual with a disabling condition who has been either continuously homeless for at least one year or homeless at least four times in the past three years [3].

The phrase "homeless people" implies a static population and a homogeneity that belies the remarkable diversity of people who lose housing. In our practice, persons experiencing homelessness range from those who have spent their entire lives in poverty to those with advanced degrees and once-successful careers cut short by mental illness, addiction, personal tragedy, or bad luck. The resolution of a homeless experience itself does not necessarily resolve the complex health and social challenges associated with homelessness or the risk of future housing instability; as a result, many of the clinical considerations presented here remain applicable following a homelessness episode.

EPIDEMIOLOGY — There are several challenges in quantifying the number of people experiencing homelessness in the United States given its dynamic nature; for most individuals, homelessness may resolve within a few months, while for others it may persist [4].

In the United States, homelessness has gradually increased since 2016. The US Department of Housing and Urban Development estimated that, on a single night in January 2020, approximately 580,000 people were homeless; of these, 226,000 slept unsheltered and more than 110,000 were chronically homeless [5]. Overall, approximately 61 percent of people experiencing homelessness reside in emergency or transitional shelters and 39 percent live in unsheltered circumstances [5].

The population of single adults experiencing homelessness is aging [6-8], in part because persons born in the latter half of the baby boom (1954 to 1967) are disproportionately likely to experience homelessness [8]. However, approximately 18 percent of those experiencing homelessness are children [5]. In addition, approximately 39 percent are female, and families represent approximately 30 percent of the United States homeless population [5].

Homelessness can be understood as a result of both "macro" and "micro" factors. Macro factors, such as the availability of low-cost rental units or the effects of an economic downturn, play a greater role in accounting for the number of persons experiencing homelessness in a particular place or from a particular group. As an example, African American persons are disproportionately represented among the homeless population in the United States [9,10], even though they are not more susceptible than White individuals to micro-level challenges such as addiction or mental illness. In the United States, disparities in wealth between racial groups, often the result of structural and institutional racism (eg, racial segregation in housing and schools), help account for the racial disparity in homelessness.

MORTALITY — Mortality rates among persons experiencing homelessness are higher than the general population [11-22]. In a 1985 to 1988 study of the homeless population in Philadelphia, the age-adjusted mortality rate was 3.5-fold higher than in the general population [23]. In a 1991 to 2001 nationwide study of people residing in shelters, rooming houses, and hotels in Canada, the all-cause mortality rate exceeded that in the nation's lowest income quintile, suggesting that homelessness may confer health risks beyond those associated with poverty alone [11].

Mortality disparities are particularly stark among youth and young adults experiencing homelessness, whose mortality rates are approximately 8- to 11-fold higher than in a comparably aged non-homeless population [12,24]. A Danish study found that the life expectancy of 15- to 24-year-old homeless men was 22 years less than for men in the general population [17].

Mortality rates for the unsheltered homeless population, those who primarily sleep outside, are also especially high. A 2000 to 2009 prospective cohort study in Boston revealed mortality rates for the unsheltered cohort to be threefold higher than the sheltered homeless population and almost 10-fold higher than that of the general Massachusetts population [25]. Certain risk factors are associated with a further increase in mortality among this population. As an example, among a 445-person unsheltered cohort followed for 10 years in Boston, there was a fourfold increase in mortality risk associated with of the following criteria: "tri-morbidity" (defined as co-occurring medical, psychiatric, and addiction diagnoses), one or more hospital or medical respite program admissions in the prior year, three or more emergency department visits in three months, age >60 years, human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) diagnosis, cirrhosis, kidney failure, or a history of frostbite, hypothermia, or immersion foot [26].

The most common causes of death among adults experiencing homelessness have shifted over time but continue to reflect a heavy burden of addiction-related illness. A considerable decline in HIV-related deaths has been offset by significant increases in deaths due to drug overdose and substance use disorders [12,22,27,28]. Overall, more than one-half of all deaths among the homeless population are attributable to tobacco, alcohol, or drug use, and drug-attributable mortality rates exceed those in the general population 8- to 17-fold [29]. While drug overdose is the leading cause of death overall and accounts for one in three deaths among those under the age of 45 years, cancer and heart disease remain the predominant causes of death among older homeless individuals [12].

Risk factors for death at baseline may be different from those that emerge in follow-up. For example, in a prospective follow-up of homeless adults over the age of 50, risk factors associated with increased mortality included new and/or recurrent episodes of homelessness, as well as self-report of fair/poor health, diabetes, and a first experience of homelessness after age 50 [21]. Recurrent homelessness may not be causal in relation to subsequent mortality, but such episodes are associated with additional risk.

HEALTH CARE UTILIZATION — Homeless persons have higher rates of medical and psychiatric hospitalization and emergency department use compared with the general population [30-38]. In addition, evidence suggests that discharges "against medical advice" and 30-day hospital readmissions are also higher in this population [39]. The pattern of acute care use among persons experiencing homelessness may be related to the high prevalence of substance use disorders and mental illness in addition to poor access to primary and preventive care services. Over one-half of adults experiencing homelessness lack a usual source of health care [40]. These individuals report a substantial burden of unmet need for basic health services, including medical care, prescription medications, mental health care, eyeglasses, and dental care [41-46]. Of those prescribed a medication, approximately one-fourth have difficulty adhering to it [47]. (See 'Substance use disorders' below and 'Mental illness' below.)

Health insurance is a critical determinant of health care access for people experiencing homelessness. Those with health insurance coverage are more likely to use ambulatory and non-hospital care services [31,48]. Compared with homeless adults who have health insurance, uninsured homeless adults are more likely to report an unmet need for health care or prescription medications [41] and are less likely to have a usual source of care [49]. National studies have suggested that approximately 60 percent of homeless people lack health insurance [31,41], although this figure has likely decreased under the Affordable Care Act. However, evidence from Canada [35,50], the US Department of Veterans Affairs system [37], and Massachusetts [36,51] suggests that universal health insurance alone is unlikely to resolve the access problems or adverse utilization patterns of those experiencing homelessness.

Additionally, subsistence difficulties and competing life priorities may adversely impact health care utilization patterns. Homeless people who sometimes or often do not get enough food to eat are more likely to be medically or psychiatrically hospitalized and are more likely to be high users of emergency department services [34,41]. Individuals with high levels of difficulty in meeting their needs for food, shelter, clothing, and safety are less likely to have a usual care source and more likely to go without needed health care [40,52].

COMMON HEALTH CONDITIONS — A number of health conditions occur more frequently among those experiencing homelessness; other conditions are seen with comparable frequency as in the general population but are often more poorly controlled. In a survey of homeless adult community health center patients in the United States, over 50 percent rated their health as fair or poor [53], compared with 17 percent among a general adult population [54].

The relationship between homelessness and poor health is bidirectional [55]. Certain conditions such as psychiatric illness or substance use disorders may increase susceptibility to homelessness. Conversely, homelessness may cause or exacerbate health problems through increased exposure to violence, poor nutrition, substandard living conditions, and communicable diseases.

The diagnosis and treatment of these conditions are presented in individual topic reviews as noted.

Skin and foot problems — These are among the most frequently cited reasons that homeless people seek medical care [56].

●Dermatophytoses – Infrequent opportunities to remove or change socks and shoes, combined with reliance on shared shower facilities, place homeless people at high risk for fungal infections involving the feet. In a study of homeless men who used a shelter-based clinic in Boston, 38 percent had tinea pedis (picture 1 and picture 2) and 15 percent had toenail onychomycosis (picture 3) [57]. (See "Dermatophyte (tinea) infections" and "Onychomycosis: Epidemiology, clinical features, and diagnosis".)

●Arthropod infestations – Scabies, lice, and bed bug infestations often accompany the adverse living conditions associated with homelessness. (See "Scabies: Epidemiology, clinical features, and diagnosis" and "Pediculosis capitis" and "Bartonella quintana infections: Clinical features, diagnosis, and treatment".)

In a study of 930 homeless clinic patients in France, 22 percent had skin lesions suggestive of body lice infestation [58]. In another study of homeless persons in California, among 203 people who reported itching, 30 percent had body lice [59]. In addition to causing bothersome dermatologic symptoms, body lice are vectors for Bartonella quintana, which has been associated with cases of "urban trench fever," septic arthritis, and endocarditis [59-63]. (See "Bartonella quintana infections: Clinical features, diagnosis, and treatment".)

In a 2003 survey of 65 homeless shelters in Toronto, over 30 percent of facilities reported past or current bed bug infestations [64]. At one affected shelter, 4 percent of the residents reported bed bug bites. (See "Bedbugs".)

●Bacterial infections – Cellulitis occurs commonly among homeless individuals [65], and the congregate nature of shelter life increases the risk for infections involving methicillin-resistant Staphylococcus aureus (MRSA) [66-68]. (See "Methicillin-resistant Staphylococcus aureus (MRSA) in adults: Epidemiology".)

●Mechanical problems – Painful corns and calluses, often the result of ill-fitting shoes and an ambulatory lifestyle, were the most common foot conditions seen among homeless individuals in one study [69]. (See "Overview of benign lesions of the skin", section on 'Calluses and corns'.)

Homeless people who sleep upright on chairs are at risk for venous stasis disease and associated dermatitis [70,71]. (See "Clinical manifestations of lower extremity chronic venous disease".)

●Exposure-related conditions – Homeless people are at high risk for exposure-related skin conditions such as frostbite and immersion ("trench") foot [69,72,73]. Although rarely fatal, these conditions may herald an underlying vulnerability to worse health outcomes. In a study of homeless adults in Boston, individuals with a history of frostbite, trench foot, or hypothermia had eightfold higher odds of death [74]. (See "Frostbite: Emergency care and prevention".)

Respiratory infections and disorders — Those experiencing homelessness are at risk for both infectious and noninfectious respiratory diseases.

Infections — Homelessness is a risk factor for tuberculosis (TB) infection [75]. The risk for TB increases with greater time spent homeless and living in crowded circumstances [76-79]. Approximately 6 percent of all active TB cases in the United States occur in homeless people, and one-third of homeless people with TB are co-infected with HIV [80]. A case series of 91 homeless people with active TB in Toronto found that many presented with advanced disease and 19 percent died within 12 months of diagnosis [81]. (See "Epidemiology of tuberculosis".)

Although the rates of TB infection are disproportionately high among homeless people, other bacterial and viral infections of the respiratory tract are far more common overall [82,83] and account for a substantial number of health care visits [84]. Homeless persons have higher rates of death due to pneumonia and influenza in comparison to non-homeless persons [11,27].

COVID-19 — During the global coronavirus disease 2019 (COVID-19) pandemic, infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may spread easily among people experiencing homelessness, especially those living in shelters [85-89].

For example, after exposure to a small cluster of infected residents, subsequent testing of all remaining 408 residents of a Boston homeless shelter revealed that 36 percent were infected with SARS-CoV-2, 88 percent of whom were asymptomatic [85]. Studies conducted in Seattle and Atlanta found similarly high rates of asymptomatic infection at the time of diagnosis [86,90].

These studies highlight the challenges of identifying the optimal surveillance and testing strategies in this high-risk population, as well as the difficulties of managing COVID-19 in a setting where isolation is not possible [85,86]. During the COVID-19 pandemic, municipalities rapidly implemented various testing protocols in addition to non-hospital alternate care sites, including temporary medical tents, empty dormitory or hotel rooms, and repurposed indoor spaces, for isolation and management of homeless individuals with COVID-19 [89]. Modeling studies conducted in the United States and England have projected that such measures are likely to reduce infections, hospitalizations, deaths, and costs relative to no intervention [91].

The risk of SARS-CoV-2 infection appears to be lower among unsheltered homeless persons as opposed to those residing in shelters [90]. For this reason, US Centers for Disease Control and Prevention (CDC) guidance on reducing the spread of SARS-CoV-2 recommends not disbanding encampments if individual housing options are not available, although sufficient space between individual sleeping areas should be encouraged [92].

COVID-19 vaccination is an essential preventive strategy to reduce the burden of infection among those experiencing homelessness, but vaccination coverage among this group is likely to be less than that of the general population. In a 2021 CDC survey of six United States urban districts, full vaccination coverage was 11 to 37 percent lower among homeless individuals compared with the general population [93]. However, all included communities relied upon homeless denominator estimates at risk for undercount (eg, single-point-in-time and service use records); thus, the difference in vaccination coverage is likely to be greater than suggested.

The CDC has issued additional interim guidance to support people experiencing homelessness, including vaccine implementation, during the COVID-19 pandemic [92,94].

Chronic obstructive pulmonary disease — The high rate of smoking among homeless persons contributes to a disproportionately high burden of obstructive lung disease [95]. (See "Chronic obstructive pulmonary disease: Risk factors and risk reduction".)

Sexually transmitted and bloodborne infections

●HIV infection – An estimated 3 to 11 percent of homeless people have HIV infection [96-100]. In addition, contemporary HIV outbreaks appear to disproportionately impact people experiencing homelessness [101,102]. Despite concerns about medication noncompliance and viral resistance [103], evidence suggests that the majority of homeless individuals treated for HIV have good adherence [104]. Once-daily medication regimens for HIV have further decreased concerns about adherence and have likely contributed to the substantial reduction in HIV deaths among homeless people [12]. Nevertheless, the circumstances of homelessness may complicate HIV management. In longitudinal study of 922 HIV-positive people who use drugs in Vancouver, Canada, the odds of HIV viral suppression decreased by 29 percent for every six months that a person spent homeless, even after controlling for drug use patterns and other confounders [105]. (See "Primary care of adults with HIV".)

●Hepatitis – The estimated prevalence of hepatitis C virus (HCV) infection in homeless persons is 12 to 42 percent [100,106-108]. The advent of newer, non-interferon-based treatments for HCV infection may prove useful for homeless individuals previously thought to be poor candidates for treatment. Studies of HCV treatment among homeless-experienced individuals in real-world clinical settings have documented high rates of treatment completion and virologic cure [109,110], emphasizing the feasibility of treating a vulnerable population at high risk for hepatic fibrosis [111]. However, cost and lack of insurance coverage of these medications may limit their availability in some settings. (See "Overview of the management of chronic hepatitis C virus infection".)

While considerably less common than HCV, hepatitis B virus (HBV) infection is also more prevalent among homeless people than in the general population. Studies estimate that approximately 30 percent of homeless people have evidence of prior exposure to HBV, and 1 to 3 percent show evidence of current infection [99,100,112,113]. (See "Hepatitis B virus: Overview of management".)

●Other sexually transmitted infections – These infections may be particularly common among homeless people who in engage in sex work or other high-risk sexual practices [114] and among those with histories of intimate partner violence, substance use, or incarceration [115]. Among 203 homeless people who underwent interviews and physical examinations in Baltimore, 8 percent of men and 11 percent of women had laboratory evidence of gonorrhea or syphilis infection, and nearly one-third reported a history of sexually transmitted infections [116]. (See "Screening for sexually transmitted infections".)

Cognitive and functional impairment — Cognitive and functional impairments are common among homeless individuals and resemble those seen in much older individuals in the general population [6,117-119]. As an example, among 1500 homeless adults with mental illness enrolled in a housing trial in Canada, 72 percent had cognitive impairment, including deficits in verbal learning and recall [120]. In addition, in a study of homeless adults ≥50 years old, 24 percent had a Mini-Mental State score <24 (the threshold for mild cognitive impairment), one-third had difficulty performing at least one activity of daily living (ADL), and over one-half had fallen within the prior year [121]. At 12 months, ADL impairments persisted in half of those affected at baseline, and an additional 15 percent of participants developed new functional impairments [122].

Chronic pain and musculoskeletal conditions may contribute to these functional impairments. Chronic pain syndromes involving the back, knees, shoulders, and feet are common in homeless persons, are frequently debilitating, and are compounded by the stressors of homelessness [123]. In a study of homeless persons in Baltimore, investigators found evidence of a musculoskeletal condition in 38 percent of men and 45 percent of women [116]. Among 350 homeless adults ≥50 years old in Oakland, 47 percent reported chronic moderate to severe pain with high levels of interference with general activity and life enjoyment. In a national survey of veterans who had experienced homelessness, 38 percent reported severe chronic pain [124].

Traumatic brain injury — A history of traumatic brain injury is more common among homeless people than in the general population and may contribute to cognitive impairment. Several studies estimate a prevalence of approximately 50 percent [125-127], with an annual incidence estimated at 18 to 19 percent [128]. In a registry-based study of homeless adults in Glasgow, hospitalization for head injury was five times more common in the homeless population compared with the general population and was associated with substantially increased all-cause mortality [129]. A majority of homeless individuals with head injuries report that their first injury occurred before they became homeless, raising the question of whether traumatic brain injury may be a risk factor for homelessness [125,127]. However, a study of military veterans found a modest association between traumatic brain injury and becoming homeless only among a subset of non-deployed males [130]. Additional research is needed to clarify the link between head injury and homelessness in both general and military veteran settings. (See "Traumatic brain injury: Epidemiology, classification, and pathophysiology".)

Cardiometabolic disorders — Although coronary artery disease, hypertension, dyslipidemia, and diabetes are not more prevalent among homeless individuals [131], they are often more advanced or more poorly controlled, contributing to high rates of cardiovascular death [132]. A Canadian study of homeless people found that 35 percent had elevated blood pressure, but only one-third of these individuals were aware of having hypertension and only 17 percent were taking blood pressure medications [133]. Another study of adults in New York City shelter-based clinics found that 40 percent of homeless individuals with hypertension had uncontrolled blood pressure [134]. In an analysis of a 27-state database of inpatient admissions for myocardial infarction, homeless patients had similar in-hospital mortality but were twice as likely to experience hospital readmission, although disproportionately for psychiatric causes rather than cardiac ones [135].

Among homeless people with diabetes in Toronto, 44 percent had a hemoglobin A1c value above 7 percent [136]. In a nationwide study of 1,263,906 veterans with diabetes who used Veterans Health Administration services, homeless individuals had a higher likelihood of poor glycemic control, even after controlling for comorbid conditions like mental illness and substance use [137]. Limited dietary choices at shelters, difficulty coordinating medication usage with meals, and logistical challenges with storing and administering insulin are just a few of the many barriers that homeless diabetics face in self-managing their illness [136]. (See 'Medication prescribing' below.)

Dental problems — Dental care is another one of the most frequently cited health needs of homeless people [138]. In a national survey of homeless veterans, 60 percent rated their oral health as fair or poor [139]. Among patients of a shelter-based dental program in Boston, 91 percent of those examined had untreated dental caries [140]. Missing teeth are common [116].

PSYCHOSOCIAL ISSUES — There is a high prevalence of substance use disorders and mental illness among homeless persons.

Substance use disorders — Available evidence has consistently suggested a higher burden of substance use disorders among homeless people than in the general population. Prevalence estimates vary depending upon the subset of the population being sampled and the instrument used [6,141].

●Tobacco – An estimated 68 to 81 percent of homeless adults are current cigarette smokers [95,142-145], and homelessness is independently associated with twofold higher odds of being a current smoker [146]. This contributes to a more than a twofold higher incidence of lung cancer [147] and three- to fivefold higher rates of tobacco-attributable mortality [29]. Despite interest in quitting [143,146,148], quit rates among homeless smokers are approximately one-fifth the national average [142].

●Alcohol – There is a variable but overall high prevalence of alcohol use disorder among those experiencing homelessness. As an example, an estimated 29 to 63 percent of homeless individuals have a history of alcohol use disorder, contributing to 6- to 10-fold higher rates of alcohol-attributable mortality than in the general population [98,116,141,149-153]. In addition, in a study of over 5000 veterans with recent homeless experience, 3.7 percent reported an alcohol overdose that required urgent medical attention in the preceding three years [124].

The prevalence of high-risk alcohol use varies, with higher rates seen among those who are currently homeless. As an example, 5 percent of previously homeless veterans assessed in primary care reported ongoing high-risk alcohol use [154] compared with 15 percent of older, currently homeless adults [155].

●Other drugs – An estimated 20 to 60 percent of homeless individuals have a history of a drug use disorder [98,116,141,149-153,156]. Marijuana, cocaine, and opioids are the most commonly used substances [156]. However, when homeless individuals are surveyed, ongoing drug use is less common than a history of past use [154,155].

Mental illness — As with estimates of substance use disorders, mental illness prevalence estimates among homeless people have varied widely from 15 to 90 percent, owing in part to differences in sampling strategies and assessment methods [141,157,158]. In a community-based probability sample of homeless adults in Los Angeles, the lifetime prevalence of severe and persistent mental illness was 28 percent, including a 14 percent lifetime prevalence of psychotic disorders and a 30 percent lifetime prevalence of major affective disorders [150].

Milder forms of mental illness are even more common, with one national study reporting that over two-thirds of homeless community health center patients had significant symptoms of psychological distress in the past month [53].

Violence and victimization — Violence and traumatic victimization are frequent precipitants of homelessness and common experiences among those who are homeless [159-162]. Among 516 adult patients of Health Care for the Homeless clinics in five United States cities, nearly two-thirds had witnessed a violent attack on another homeless individual and one-half had been the victim of an attack while homeless [163].

In a Massachusetts study of homeless women, 63 percent had experienced severe violence by an adult partner, 43 percent had been sexually molested as a child, 67 percent had experienced severe physical abuse as a child, and 88 percent had experienced at least one of these forms of violence in their lifetime [164]. Such experiences are not confined to women. Two California studies found that over 20 percent of homeless men have been physically or sexually assaulted in the recent past [165,166]. This estimate approached 40 percent among transgender individuals. National studies have yielded similar estimates [41].

Hate crimes against homeless people are another area of emerging concern. Between 1999 and 2008, the National Coalition for the Homeless estimated that 880 hate crimes were perpetrated against homeless people, including 244 resulting in death [167].

CLINICAL MANAGEMENT

Overall approach — "Homeless health care" is truly just an extension of "patient-centered care" that sometimes seems exotic because of the unique blend of comorbidities and social challenges that patients bring to the table. Although homelessness presents unique health risks, the biology of illnesses and their treatment are fundamentally the same as in any other population and are covered in individual topic reviews.

For chronic diseases such as diabetes or hypertension, every effort should be made to adhere to evidence-based general population guidelines. However, the approach to providing care for homeless people may need to be modified to account for the extreme circumstances of their daily lives. For example, it may not be feasible or safe to aim for the recommended glycemic goals for diabetic patients or to initiate anticoagulation for atrial fibrillation in patients with high stroke risk. (See "Overview of general medical care in nonpregnant adults with diabetes mellitus", section on 'Blood glucose monitoring and target A1C' and "Atrial fibrillation in adults: Use of oral anticoagulants".)

●Outreach-based approach – For most homeless individuals, competing priorities for food, shelter, clothing, and safety often supersede the perceived importance of routine health care [52]. Thus, traditional clinical models that rely upon patients presenting for medical care in a timely and self-guided fashion are suboptimal for this population. Instead, we advise an outreach-based approach that embeds clinical services in the places that homeless people frequent by necessity: shelters, soup kitchens, and drop-in centers. A team-based street outreach model may be needed to reach those who avoid such services and sleep outside. The organizational framework to support this care varies by community.

Outreach interventions may improve access to care. As an example, in a randomized trial of 185 homeless veterans, an outreach intervention improved access to primary care at six months compared with usual care (90 percent versus 37 percent) [168].

●Engagement – Some homeless individuals will engage quite readily, while others, particularly those with more severe psychiatric illness, may be reluctant to engage in formal health care services [169]. We use a variety of low-pressure techniques for engaging the subset of people who are profoundly mistrustful. In such settings, we focus on tangible issues, and we avoid medicalizing their concerns. Humane gestures that address basic subsistence needs, such as giving out socks or food vouchers, may be helpful, but we advise against giving out tobacco or alcohol to build trust. In many cases, we offer foot soaking and cleansing because this addresses an immediate need, inverts the traditional patient-clinician power dynamic, and conveys a service-oriented approach to care [170].

●Trauma-informed approach – Given the pervasiveness of traumatic life experiences among homeless people, we use a trauma-informed approach throughout the care process [171]. In a primary care setting, trauma-informed care includes universal screening for histories of trauma, educating office staff to be sensitive to issues of physical and emotional boundaries, allowing patients to help dictate the pace and direction of history-taking, physical examination, and invasive diagnostic testing, and proceeding cautiously with assessments that may inadvertently re-traumatize patients (eg, pelvic examinations).

History gathering — A comprehensive history may not be feasible or even desirable during the initial clinical encounter, particularly among those who are guarded about engaging in care. More often than not, we gather the history incrementally over several visits while building rapport and trust. We advocate for a patient-centered approach to history gathering that allows patients to guide the pace and direction of initial health conversations.

In addition to a customary medical history, it is critical to document and update contact information, as this often changes. A large percentage of homeless people have cell phones, although their allotment of minutes may be limited and may fluctuate [172-174].

We pay particular attention to the social history as the patient allows [175]. We ask about where people sleep at night, with particular attention to distinguishing those who stay in sheltered locations from those who sleep "rough" in outdoor locations, since the latter group may be at particularly high risk for assault, exposure-related conditions, and other health complications. The moniker "homeless" may not be accepted by some people experiencing homelessness, so we prefer the approach of discussing episodes in and out of housing. Helpful questions may include:

●"Can you tell me where you have been staying at night this past week?"

●"Is that a place where you can continue to stay?"

●"When was the last time that you had a place you considered your own home?"

Special consideration should also be given to addressing current and past substance use as well as symptoms of mental illness. Specific screening tools may be helpful in eliciting this history. (See 'Psychiatric and addiction care' below.)

Physical examination — As in any clinical encounter, the examination should be guided by the concerns generated during history-taking and general observation. Depending upon the patient's readiness to engage, serial focused examinations may be preferable to a single comprehensive examination.

We dispense with intrusive aspects of the physical assessment that have little evidence to support them (eg, screening breast or testicular exams) [176,177]. When caring for patients with particularly severe trauma histories, we recommend an approach that openly narrates planned actions ("Now, I'm going to listen to your lungs") and seeks permission for more sensitive assessments ("Is it okay if I examine your belly?").

Some patients may be reluctant to allow an examination because of shame about certain aspects of their appearance (eg, decayed teeth) or self-care (eg, malodorous feet). In these instances, we use normalizing language ("I see all kinds of teeth; it doesn't bother me") and allow the patient to guide which aspects of the examination are acceptable.

Given the heavy burden of cognitive and functional impairments among homeless people, clinicians should consider screening for cognitive impairment and performing an office-based assessment of functioning and mobility, particularly in homeless persons ≥50 years. (See 'Cognitive and functional impairment' above and "Comprehensive geriatric assessment", section on 'Functional status' and "Evaluation of cognitive impairment and dementia".)

Laboratory testing — Given the high prevalence of HIV and hepatitis C virus (HCV) among homeless people, we offer up-front universal screening for these infections and periodic retesting for individuals at high risk. Other laboratory testing should be guided by the history and physical examination, the clinical situation, and accepted guidelines. (See "Screening and diagnosis of chronic hepatitis C virus infection" and "Screening and diagnostic testing for HIV infection" and 'Approach to preventive care' below.)

Point-of-care testing is preferable when feasible. A clear plan for the follow-up of abnormal test results should be constructed. For those without a cell phone or reliable contact information, we schedule follow-up visits dedicated to the review of laboratory results.

Medication prescribing — The pharmacologic management of acute and chronic illnesses should follow recommended guidelines when possible. A simple medication regimen is best. We make every effort to prescribe once-daily medications. Adherence is unlikely at dosing frequencies higher than twice daily. For homeless patients who lack health insurance, clinicians should familiarize themselves with local resources that provide medications on a low-cost or charity basis.

Specific challenges of medication prescribing in the homeless population include:

●Diabetic patients and insulin – The logistics of insulin therapy should be carefully considered in the setting of homelessness and tailored to each individual's personal resources and living circumstances. We preferentially rely on longer-acting insulin formulations that can be given once or twice daily (eg, NPH, detemir, or glargine), and we tend to avoid rapid-acting insulin regimens that require predictable eating schedules. Most types of insulin can be stored at room temperature for up to one month, but extremes of temperature should be avoided [178].

●Concerns for medication misuse – Consideration should be given to the street value of certain medications, although this should not overshadow an individual patient's medical needs. In Boston, medications such as clonidine and gabapentin (or "Johnnies") are sometimes misused to potentiate the sedating effects of opioids and benzodiazepines, conferring a higher risk of complex intoxication syndromes [179].

Given the high rates of overdose death among those experiencing homelessness, opioids should be prescribed cautiously and with close supervision in this population [12]; however, homelessness should not be viewed as an absolute contraindication to opioid prescribing. An argument can be made for providing the opioid overdose reversal agent naloxone to all patients who rare prescribed opioids, including persons who are homeless, who may require it or who may encounter others who need it. (See "Use of opioids in the management of chronic non-cancer pain", section on 'Risks of misuse and overdose' and "Management of acute pain in opioid naïve adults in the ambulatory setting", section on 'Basic measures for all patients'.)

Psychiatric and addiction care — The high burden of mental illness, substance use disorders, and drug poisoning events (overdose) among homeless people makes screening for and treating these conditions an essential aspect of care. Our experience suggests that primary care providers often play a crucial frontline role in the identification and initial management of these disorders, particularly among homeless patients who may have difficulty navigating the often complex systems of mental health care. (See 'Psychosocial issues' above.)

Single-item screens for substance use ("How many times in the past year have you used an illegal drug or used a prescription medication for nonmedical reasons?") and alcohol use ("Do you sometimes drink beer, wine, or other alcoholic beverages?") are validated in the primary care setting. In general, a positive screen necessitates subsequent formal assessment, either through a diagnostic interview (as might be offered in mental health care) or through a detailed history predicated on a trusting relationship and respectful conversation. Screening tools are also available for depression (table 1) and anxiety (table 2). (See "Screening for unhealthy use of alcohol and other drugs in primary care", section on 'Single-item screening' and "Screening for unhealthy use of alcohol and other drugs in primary care", section on 'Single-item screening' and "Screening for depression in adults" and "Generalized anxiety disorder in adults: Epidemiology, pathogenesis, clinical manifestations, course, assessment, and diagnosis".)

If onsite integrated behavioral health services are not available, primary care practitioners should familiarize themselves with the community resources available to homeless individuals. Providers should also have some familiarity with their state's legal mechanisms for the involuntary evaluation and care of individuals whose mental illness or substance use places themselves or others at imminent risk.

When available, case management services and multidisciplinary assertive community treatment models may be effective strategies for homeless people with serious mental illness and substance use problems [180-183]. Less intensive shelter-based collaborative mental health care models may also achieve favorable outcomes in functioning, housing, and health care utilization [184]. Post-detoxification stabilization programs may be effective strategies for reducing alcohol and drug use among substance-dependent homeless people [180,185,186].

Drug poisoning or overdose events may occur in individuals with a diagnosable substance use disorder, or among persons whose use brings them into contact with substances or drug combinations of unexpectedly high potency. Where opioid use disorder is diagnosed, office-based medication treatment for opioid dependence is feasible and lifesaving in this population, but longer-term adherence may pose a challenge. Among opioid-dependent patients managed with outpatient buprenorphine in an urban safety net setting, those who were homeless had similar outcomes to non-homeless individuals with respect to treatment failure, illicit opioid use, and utilization of substance use treatment [187]. In a 2003 to 2018 longitudinal study of homeless-experienced patients with opioid use disorder engaging in outpatient buprenorphine treatment, program attendance conferred a 66 percent reduction in all-cause mortality, although overall retention in care was suboptimal (45 percent at one month), emphasizing the need for interventions to improve treatment adherence over time [188]. (See "Opioid use disorder: Pharmacologic management".)

Conversely, even where clinicians have not diagnosed a substance use disorder, drug poisoning remains a risk because the North American illicit drug market features unpredictable combinations of illicitly derived fentanyl and other substances, sometimes sold as heroin, as stimulants, or in pressed tablet form. We offer naloxone to all patients who engage in the illicit drug market. (See "Primary care management of adults with opioid use disorder", section on 'Harm reduction interventions'.)

Approach to preventive care — When possible, patients should receive age-appropriate preventive care. Preventive care and screening should be guided by the clinical situation and accepted guidelines. We partner with patients to determine the order and priority of pursuing preventive care measures. (See "Overview of preventive care in adults".)

Given the preponderance of communicable diseases among homeless people, we emphasize the importance of immunizations against influenza, pneumococcus, Tdap, and hepatitis A and B in patients for whom these vaccines are appropriate. (See "Seasonal influenza vaccination in adults" and "Pneumococcal pneumonia in patients requiring hospitalization" and "Tetanus-diphtheria toxoid vaccination in adults" and "Hepatitis A virus infection: Treatment and prevention" and "Hepatitis B virus immunization in adults".)

Although cancer is a leading cause of death among older homeless adults [12], individuals with frequent subsistence difficulties may prioritize the daily pursuit of food, shelter, and safety over the more distant and less tangible benefits of cancer screening. Colorectal cancer screening in particular poses several challenges in the setting of homelessness, and studies have documented low completion rates among homeless individuals [53,189-191]. Medical respite facilities may play an important role in overcoming the challenges of colonoscopy preparation while homeless. Additionally, we perform in-office Pap testing and work closely with area hospitals to facilitate same-day or near-future screening mammography for women who desire these tests. (See 'Tailored care models' below.)

Recommendations for preventive care and screening are discussed in detail elsewhere. (See "Geriatric health maintenance" and "Overview of preventive care in adults".)

Prenatal care — Prenatal care for females experiencing homelessness is discussed in detail elsewhere. (See "Prenatal care for people experiencing homelessness".)

HOUSING INTERVENTIONS — A growing evidence base has examined the health and social impacts of providing housing to people experiencing homelessness. As an example, in a study of almost 5000 homeless people with serious mental illness in New York City between 1989 and 1997, those who were placed in supportive housing (subsidized housing with onsite or linked supportive services, such as medical and psychiatric care and case management) had an 86 percent decrease in shelter use, 57 percent fewer inpatient psychiatric days, 80 percent fewer days spent in municipal hospitals, as well as fewer days spent in prison and jail (74 percent and 40 percent, respectively) [192]. In another study of 160,525 homeless people who used the New York City shelter system between 1990 and 2002, those who entered housing had a lower mortality risk than those who remained homeless [193].

The general approach to housing provision has been an area of some controversy:

●Linear approaches – Early housing models were largely based upon a "linear" approach that made free or subsidized housing contingent upon abstinence from drugs and alcohol and progression through a continuum of treatment programming [194-196]. In a meta-analysis of randomized trials of individuals with cocaine addiction, the combination of a six-month period of abstinence-contingent housing coupled with addiction day treatment resulted in higher abstinence rates compared with day treatment alone or usual care [197]. However, maintenance of durable housing six months after treatment completion was elusive, and fewer than 40 percent were housed at 12 months [198]. Outcomes observed outside of addiction treatment trials are somewhat better, with 63 percent achieving durable housing by two years [199].

Given these results, critics of the linear housing approach have questioned the rationale for requiring abstinence or treatment engagement prior to housing entry, while also raising concern that housing should be offered as a positive human right [194]. In some studies, there was minimal or no association between housing outcomes and program requirements for abstinence or residential treatment program completion [195,200,201].

●Housing First – In contrast with a linear housing approach, the "Housing First" approach uncouples the provision of housing from engagement in substance use treatment services [196,202]. Proponents of Housing First generally view the attainment and maintenance of housing, rather than sobriety, as the principal outcome [203].

Similar to linear approaches, Housing First models often incorporate comprehensive support services from multidisciplinary teams of health and social service professionals. Studies of Housing First for homeless individuals demonstrate clear improvements in housing stability compared with usual care, but inconsistent improvements in other social and health benefits. As examples:

•Pathways to Housing, a randomized controlled trial in homeless people with serious mental illness and comorbid substance use disorder, compared participants offered the linear housing versus the Housing First approach [202]. Those participating in Housing First spent over twice as much time in stable housing, with no differences in substance use outcomes or psychiatric symptoms.

•Among a group of chronically homeless people with severe alcohol use disorders in Seattle, Housing First was associated with reduced alcohol consumption as well as significant reductions in public service use and costs [204,205].

•In a randomized trial of homeless individuals with chronic medical conditions in Chicago, those participating in Housing First had reductions in hospital days and emergency department use compared with usual care [206]. In this study, among those with HIV, survival with intact immunity was greater in those who received the Housing First intervention [207].

•In a randomized trial of homeless Canadians with mental illness, the effect of rent subsidies coupled with either Housing First with intensive case management (ICM) or assertive community treatment (ACT) was compared with usual care [208]. Among individuals with moderate support needs, participants in the Housing First plus ICM arm had improved housing stability but did not differ from usual care participants in generic quality-of-life or health indicators at two-year follow-up [209]. Among individuals with high support needs, Housing First plus ACT resulted in greater improvements in residential stability, overall quality of life, and community functioning compared with usual care at one-year follow-up [210]. Among this group, improvements in quality of life and community functioning were attenuated at two years but remained significant [211].

Because homelessness impedes health care, Housing First interventions are sometimes advocated as meriting support through health assistance programs, such as Medicaid in the United States [212]. However, although Housing First programs may reduce use of some costly services in hospitals or shelters [213], they do not assure a net savings to society [214], and the evidence for their impact on health remains mixed. For example, in an analysis of 292 participants in a Housing First program, men aged 45 to 64 had a nearly five-time higher mortality than adults in their general community, principally from medical disease [215]. In addition, a 2018 panel of the National Academies of Sciences, Engineering, and Medicine found a lack of high-quality data that housing interventions reliably improve health or reduce cost, outside of studies focused on persons with HIV/AIDS [216]. Despite the lack of supporting evidence for documented improvement in health outcomes, however, the panel experts concluded that access to housing will improve health.

TAILORED CARE MODELS

●Health Care for the Homeless Program – Since the original inception of the program, the Health Care for the Homeless (HCH) program has grown to include more than 300 federal grantees that provide care to over one million people annually [217-219].

HCH programs vary greatly in their size and delivery models but often share a commitment to providing health care services that are tailored to meet the needs of homeless individuals and families. These programs generally seek to provide integrated, team-based care through co-located medical, mental health, and substance use treatment services. Core components of the HCH model include outreach and engagement, community collaborations, case management services, medical respite care, and guidance from consumer advisory boards [220].

●Veterans Affairs Homeless Patient Aligned Care Team – In 2012, the US Department of Veterans Affairs set up the Homeless Patient Aligned Care Team (H-PACT) primary care design as an extension of their PACT model of team-oriented primary care. The H-PACT model resembles the HCH approach in emphasizing co-located services across a continuum of health and social needs, including medical care, case management, housing assistance, behavioral health treatment, benefits counseling, and other onsite social services. These services may have favorable effects on emergency department use, especially for preventable or avoidable reasons [221]. In addition, among veterans with a similar homeless experience, those who utilize H-PACTs rate their primary care more favorably compared with standard VA primary care clinics [222].

●Medical respite care – A signature concept of the HCH model is medical respite care, which provides a safe, sheltered, and medically supervised environment for the care of homeless individuals who are too medically compromised to be on the streets or in a shelter, but not ill enough to merit acute care hospitalization [223]. Medical respite units are particularly well-suited to providing care to homeless individuals following hospital discharge; studies show reductions in 90-day readmission rates [224], 30-day readmission rates among frequently hospitalized patients [225], and total hospital days over 12 months [226]. In practice, medical respite units are also useful venues for stabilizing poorly controlled chronic conditions such as diabetes, managing acute conditions such as influenza or cellulitis that may not require hospitalization, and providing supportive care surrounding ambulatory procedures such as colonoscopy or day surgeries such as herniorrhaphy. With the aging of the homeless population, increasing attention has turned toward end-of-life care for homeless people [227,228], and medical respite programs could potentially play an important role in addressing this need as well.

RESOURCES — Several organizations have free web-based materials relevant to the medical care of homeless people:

●The National Health Care for the Homeless Council has an extensive collection of online resources related to policy, advocacy, clinical practice, medical respite care, and training and technical assistance.

●The National Coalition for the Homeless has several concise Fact Sheets on homelessness.

●The Centers for Disease Control and Prevention has developed a comprehensive set of online resources to support people experiencing homelessness during the coronavirus disease 2019 (COVID-19) pandemic.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Medical care for homeless persons".)

SUMMARY AND RECOMMENDATIONS

●Definition and epidemiology – In the United States, a homeless person is defined as someone who lacks a fixed, regular, and adequate nighttime residence and who lives in a shelter or a place not designed for human habitation; people at imminent risk of housing loss within the next two weeks; and people fleeing from domestic violence with inadequate resources to obtain other permanent housing. The phrase "homeless people" implies a static population and a homogeneity that belies the remarkable diversity of people who lose housing. Persons experiencing homelessness range from those who have spent their entire lives in poverty to those with once-successful careers cut short by mental illness, addiction, personal tragedy, or bad luck. The resolution of a homeless experience itself does not necessarily resolve the complex health and social challenges associated with homelessness or the risk of future housing instability; as a result, many of the clinical considerations presented here remain applicable following a homelessness episode. In the United States, homelessness is increasing. (See 'Definition' above and 'Epidemiology' above.)

●Increased mortality risk – Mortality rates among homeless people are higher than in the general population. Mortality disparities are particularly stark among youth and young adults experiencing homelessness, and they are also high for the unsheltered homeless population, who primarily sleep outside. (See 'Mortality' above.)

●Health care utilization – People experiencing homelessness have high rates of hospitalization and emergency department use but poor access to primary medical care and a high burden of unmet need for basic health services. (See 'Health care utilization' above.)

●Common health conditions – A number of specific health conditions (eg, skin and foot problems, respiratory infections, dental problems) occur more frequently among people experiencing homelessness, while other conditions seen with comparable frequency with the general population are often more poorly controlled (eg, hypertension, diabetes). Substance use disorders, mental illness, and victimization are also more common among people experiencing homelessness than in the general population. (See 'Common health conditions' above and 'Psychosocial issues' above.)

●Clinical management – Although homelessness presents unique health risks and social challenges, the biology of illnesses and their treatment are fundamentally the same as in any other population. (See 'Clinical management' above.)

•We use an outreach approach that embeds clinical services in the places that homeless people frequent by necessity. We use low-pressure techniques for engagement and allow the patient to dictate the pace of care, particularly for those who have experienced trauma. The treatment of illnesses in those experiencing homelessness is the same as for the non-homeless population, but the approach to care may need to be tailored to an individual's circumstances and resources. (See 'Overall approach' above.)

•We often take an incremental approach to the history and physical examination. We document and update contact information and pay particular attention to the social history as the patient allows. Clinicians should consider screening for cognitive impairment and assessing function and mobility, particularly in homeless persons ≥50 years old. (See 'History gathering' above and 'Physical examination' above.)

•We use point-of-care lab testing when available. We offer universal screening for HIV and hepatitis C virus (HCV). We create a concrete follow-up plan for discussing the results of time-delayed tests. (See 'Laboratory testing' above.)

•A simple medication regimen is best. We make every effort to prescribe once-daily medications. (See 'Medication prescribing' above.)

•The high burden of mental illness and substance use disorders among homeless people makes screening for these conditions an essential aspect of care. Where available, case management services and multidisciplinary assertive community treatment models may be effective in treating mental illness and substance use. (See 'Psychiatric and addiction care' above.)

•When feasible, patients should receive age-appropriate preventive care and screening. We prioritize indicated vaccinations against infectious illnesses. (See 'Prenatal care' above and 'Approach to preventive care' above.)

●Housing interventions – Selected housing interventions have been associated with improved social outcomes and, in some instances, health benefits or cost offsets. Although early housing models tended to emphasize an abstinence-based approach, the Housing First approach places no requirements on sobriety or treatment participation and is associated with improved housing tenure without apparent worsening of substance use outcomes. (See 'Housing interventions' above.)

●Tailored care models – Health Care for the Homeless (HCH) program clinics provide tailored services in a multidisciplinary environment. Medical respite units may be useful for homeless individuals requiring posthospital care, stabilization of acute and chronic health conditions, and supportive care around ambulatory procedures (eg, colonoscopy). Such programs appear to reduce rehospitalization following hospital discharge. (See 'Tailored care models' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Stewart Rogers, MD, and James O'Connell, MD, who contributed to earlier versions of this topic review.