Characterizing traumatic brain injury in unsheltered homelessness: prevalence of TBI and cognitive sequelae in individuals utilizing street medicine
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Graham Atkin
,
Jessica Reece
Abstract
Context
People experiencing homelessness are at a disproportionately greater risk for developing traumatic brain injury (TBI) than the general population. There has been minimal research to evaluate the prevalence of TBI or the long-term cognitive impacts of TBI among the population experiencing homelessness within the United States. There is minimal literature that examines individuals who are living unsheltered, especially regarding TBI.
Objectives
This study aimed to assess primarily whether those experiencing unsheltered homelessness had a higher prevalence of TBI than those in shelter. Furthermore, we examined the differences in the prevalence of repeated TBIs, TBI by age of respondent, loss of consciousness (LOC), and cognitive symptoms in people experiencing homelessness across three housing strata (sheltered, low-barrier sheltered, and unsheltered) within a small midwestern city.
Methods
Participants were recruited utilizing a convenience sampling of patients who utilized street medicine healthcare services. The study enrolled 102 patients during the interval of October 2022 through March 2024 from three housing strata (sheltered, low-barrier sheltered, and unsheltered) in Lansing, Michigan. We employed the Ohio State TBI Identification Method, abbreviated for ease of use. Results were analyzed for associations between TBI and health conditions utilizing chi-squared tests and a single difference-of-proportions test.
Results
Seventy-five of 102 (73.5 %) of participants reported at least one TBI, with 48 % experiencing their first TBI more than 20 years ago. There was a significant difference in TBI prevalence across housing strata. Ninety percent (90 %) of unsheltered survey respondents reported at least one previous TBI, with 50 % reporting three or more previous TBIs. These rates exceeded those of respondents in shelter (58 % prevalence, 21 % 3+ TBIs) and low-barrier shelter (65.1 % prevalence, 26 % 3+ TBIs), all of which exceeded the reported TBI prevalence for the general population (21.7 %). TBI prevalence did not vary significantly by age. LOC following TBI among participants significantly exceeded that of the general population (48 vs. 12 %). The prevalence of severe TBI was significantly greater than the general population for low-barrier shelter (16 vs. 2.6 %) and unsheltered respondents (23 %), but not for sheltered participants. Many respondents (62.6 %) developed cognitive symptoms as a result of TBI, although no statistical difference emerged between the groups. Cognitive sequalae were most common among those with three or more TBIs.
Conclusions
Taken together, these results suggest that the likelihood of TBI and the associated risks present a greater threat to those experiencing homelessness. There is a propensity to most strongly affect those living unsheltered.
While on Street Rounds, we were introduced to “Jason” (pseudonym), a US military veteran now living on the street. While overseas, Jason suffered head trauma from an improvised explosive device. Since then, he reported frequent headaches. During our encounter, his emotions were labile: he shifted quickly from laughing to yelling to suspicion to tears. Our community partners shared that Jason had been unable to remain at shelters due to his emotional – and frequently angry – outbursts. Our team questioned how substantial a role brain injury was playing in Jason’s demeanor and how many people there were like Jason, living unhoused.
Traumatic brain injury (TBI) is a worldwide clinical cause of neurological dysfunction, disability, and death. The prevalence of TBI ranges from an estimated 46 million to 51 million cases globally, with TBI occurring in North America at approximately 503 cases per 100,000 people [1]. The current understanding of global TBI disease burden is limited by factors such as ongoing conflict and disparities in access to medical care [2], 3]. The prevalence of TBI for those living in a homeless shelter [4] is more than twice that of individuals who are stably housed [5] (53.1 vs. 21.7 %, respectively). This rate increases to 81 % for those who are living in a more easily accessed low-barrier shelter [6]. The rates for those living unsheltered (e.g., in the woods, under freeway bridges, etc.) remain largely unassessed.
People experiencing homelessness are disproportionately at risk of TBI. They experience significantly higher rates of physical assault [7], 8] and intimate partner violence [9]. Other contributing factors include a lack of protective shelter, proximity to high-crime and high-traffic areas, and higher rates of substance use and mental illness [7], 8], 10]. People experiencing homelessness are 45 times more likely to die from being hit by a car [11].
Sustaining even a single TBI can result in an array of short- and long-term cognitive deficits including memory loss [12] and decreased cognitive speed [13] as well as significant psychosocial dysfunction [12] such as depression, anxiety, aggression, PTSD [14], and antisocial conduct [15]. The Wilder Homelessness Study, which surveyed 2,732 adolescents, found that youth experiencing homelessness with a history of TBI had greater difficulty performing activities of daily living [16]. Repeated TBIs are associated with increasingly diminished cognitive performance [17], and a history of TBI imparts an increased risk for dementia [18]. TBI impacts the function of cerebral blood vessels, increasing risk of stroke and hemorrhage [19]. Because even mild TBI is a source of persistent, injury-related difficulty after 1 year of injury [20], it remains paramount for osteopathic physicians to identify TBI sequelae and continue to support the individual’s ability for self-healing and self-regulation through TBI recovery.
Significant cognitive disparities for those in homeless shelters have been well established [21]. A longitudinal study of 375 homeless individuals in sheltered locations found that 68.1 % of participants had clinical impairments in verbal learning and 62.9 % had clinical impairments in verbal memory [22]. Although these differences are likely multifactorial, the evidence of the increased prevalence of TBI makes it a strong candidate for a significant contributing factor.
Further examination of TBI is critical to understanding the ongoing health and socioeconomic disparities between the general public and those experiencing homelessness. For example, access to permanent housing, homeless shelters [23], and employment [24] are often gated behind intake processes that require intact cognition and strict behavioral compliance [25], both of which are jeopardized by TBI.
The present study seeks primarily to differentiate the prevalence of TBI across three housing strata: among those living in shelter, at a low-barrier shelter, and unsheltered, all within a small Midwestern city. Furthermore, this study examines the differences in prevalence of repeated TBIs, the prevalence of TBI by participant age, loss of consciousness (LOC), and alterations to cognitive function postinjury based on housing strata.
Methods
Procedures and participants’ characteristics
All procedures were reviewed and approved by the Institutional Review Board at Michigan State University (STUDY00007783) in compliance with all applicable federal and state regulations regarding the protection of human subjects. This study was granted an exemption from full review because no interventions were performed and minimal identifying information was collected. This study was unfunded. Because no intervention was performed, this study was not entered into the clinical trial registry.
Street medicine services were offered at three types of residential sites, which are defined for the purposes of this study as follows: (1) shelters meeting the State of Michigan’s definition of a shelter (including offering beds and meals), which require sobriety and other behavioral compliances; (2) low-barrier shelters, which are enclosed buildings with bathroom and shower facilities as well as space to sleep but not beds or meals; sobriety is not required and there are lower behavioral requirements; and (3) unsheltered locations, including any location where someone is living on the street, under freeway bridges, in the woods, or any outdoor space not intended for human habitation. Participants receiving care at one of these three locations were then placed into that category for comparison.
Sampling procedures
Participants were offered the survey following their street medicine encounter and explicitly stated that participation was voluntary and not connected to receiving medical care. The purpose of this study was explained, and verbal informed consent was obtained by street medicine volunteers from all participants prior to survey administration. The survey questions were read aloud by a trained street medicine volunteer, who then transcribed the responses. Approximately 20 % of individuals seeking street medicine care were enrolled during the interval of October 2022 through March 2024, and the first 102 participants who agreed to participate in the study were included in the sample. The participants were not compensated for their time, nor did they receive any additional benefits for their participation.
Participant characteristics
Out of the 102 survey participants, the mean reported age was 50.7 years old (standard deviation [SD]=13.2; range, 20–89 years) with five individuals (4.9 %) reporting previous military service. Gender and race/ethnicity data were not collected because this information was not deemed to be necessary for planned analysis.
Of the 102 participants surveyed, 19 (18.6 %) participants were categorized as staying at a shelter, 43 (42.1 %) in a low-barrier shelter, and 40 (39.2 %) in an unsheltered location.
Measures
The Ohio State University TBI Identification Method [26] was adapted into a succinct, open-ended five-question survey; decreasing the length of the survey was based on our assessment of participants’ tolerance for survey burden (see Supplementary Material for the adapted tool). The participants provided self-reports to elicit summary indices reflecting TBIs occurring over their lifetime. Individuals were asked whether they suffered an injury that “knocked them out or at least left them dazed, confused, or disoriented.” Those endorsing these events were considered to have a history of TBI. Participants with a TBI history were asked to describe the nature and time course of these injuries, the occurrence and duration of altered consciousness, and whether these injuries led to cognitive symptoms. The specific cognitive symptoms inquired about were memory issues, difficulty concentrating, difficulty with speech, chronic headaches, and vision changes.
Statistical analysis
Comparisons between groups were accomplished with chi-squared tests. To compare results with established rates from previously published studies of the general, housed population, a single sample difference of proportions test was utilized. The Center for Statistical Training and Consulting (CSTAT) at Michigan State University assisted in calculations; all calculations were performed utilizing an online statistical calculator. GA, JR, and IM participated in the data analysis.
Results
Prevalence of TBI across housing strata
Pooling responses across all housing strata revealed that 75 of the 102 (73.5 %) study participants reported at least one TBI. The responses were analyzed for each housing stratum: 11 of those in shelters (57.9 %) had a history of TBI, compared to 28 of those at a low-barrier shelter (65.1 %); this difference was not statistically significant (p=0.587). Among the participants surveyed from an unsheltered location, 36 reported a history of TBI (90 %), which was significantly more than the other strata (p=0.009, p=0.01). Figure 1 delineates the prevalence of TBI across housing strata.
The percentage of study participants reporting a prior TBI stratified into three housing groups: sheltered (green bar), low-barrier sheltered (red bar), and unsheltered (blue bar). The participants who were identified as unsheltered reported a higher prevalence of TBI compared to those in other housing groups. There was a significantly higher prevalence of TBI in unsheltered participants vs. low-barrier sheltered or sheltered participants.
Prevalence of repeated TBIs
All participants were asked how many TBIs they experienced in their lifetime. There were four participants who did not answer this question and were excluded from this analysis. Among the 98 respondents, 21 (21.4 %) reported exactly one TBI and 56 (57.1 %) reported that they have had two or more TBIs. For comparison, the reported rate for repeated TBI in the general population varies greatly, from 0.4 to 41.9 % [27]. Taking the upper limit of 41.92 % in the literature, study participants remain at a significantly greater likelihood of having experienced repeated TBIs (confidence interval [CI]95=0.498175–0.751825; p=0.0018) than the general, housed public.
The prevalence of one, two, or three or more TBIs across housing strata were examined. For exactly one or exactly two previous TBIs, the prevalence was not significantly different between housing strata (one TBI, p=0.462; two, p=0.756). However, there was a significant difference between housing strata for participants reporting three or more previous TBIs. Unsheltered participants had the greatest prevalence, with 20 of 40 (50 %), significantly higher than the low-barrier shelter with 7 of 43 participants (26 %, p=0.021) or sheltered with 4 of 19 participants (21 %, p=0.034). There was no significant difference when comparing low-barrier and sheltered participants (p=0.650). Figure 2 demonstrates the prevalence of three or more TBIs across housing strata.
The percentage of study participants reporting ≥3 previous TBIs stratified into three housing groups: sheltered (green bar), low-barrier sheltered (red bar), and unsheltered (blue bar). The participants who were identified as unsheltered reported a higher prevalence of three or more TBIs, and there was a statistically significant difference in prevalence of ≥3 previous TBIs in unsheltered participants vs. those in other housing groups.
Prevalence by age of respondent
The respondents were compared by decade of age. Three participants did not indicate or did not know their age and were excluded from these calculations. There was no statistical difference in TBI prevalence across age ranges (p=0.200). Figure 3 depicts the total number of participants across age ranges and the participants with TBI within each age group.
Total participants per age range (blue bar) vs. the number of participants per age range reporting prior TBI (gray bar). The “Unknown” category represents the participants who did not disclose their age in the study’s survey. There was no statistically significant difference in the prevalence of TBIs across age ranges.
Among those endorsing TBI, 36 participants (48 %) experienced their first TBI more than 20 years before the survey; 9 (12 %) 10–19 years ago, 6 (8 %) 5–10 years ago, 5 (7 %) 1–5 years ago, and 19 (25 %) could not recall when they experienced their first TBI.
Loss of consciousness
Across all 102 survey respondents experiencing homelessness, 49 participants (48 %) reported LOC following TBI, a rate that is four times that of the general population [28] (CI95=0.383413–0.577372; p<0.001). Figure 4 depicts the prevalence of TBI and LOC within the general population and study participants. The rates for LOC following TBI were not significantly different across housing strata (p=0.756).
The percentage of unhoused participants reporting loss of consciousness (LOC) immediately following TBI (blue bar) vs. individuals in the general population reporting LOC following TBI (gray bar). The study participants reported a significantly higher prevalence of LOC following TBI compared to the general population.
The rate of severe TBI (defined as LOC lasting 30 min or more) in the general public is 2.6 % [5]. The prevalence of severe TBI in low-barrier and unsheltered participants was found to be significantly greater than the general population. For participants from low-barrier shelters, the rate of at least one severe TBI was 16 % (n=7; CI95=0.052423–0.273158; p<0.0001) and 23 % for unsheltered respondents (n=9; CI95=0.095564–0.354436; p<0.0001). The rate for sheltered respondents was not statistically different from the general population (n=1; CI95 = −0.047795 to 0.153058; p=0.440).
Cognitive symptoms and history of TBI
While our tool (Supplementary Material) limited cognitive symptoms to memory loss and difficulty concentrating, several respondents discussed other cognitive sequelae, including difficulties with speech, headaches, changes to vision, and new-onset seizures. Of the 75 participants in the study who reported a TBI, 47 (62.6 %) endorsed at least one cognitive symptom (difficulties with memory, concentration, speech, headaches, or vision, or new-onset seizures), including 44 participants (58.6 %) endorsing memory loss and difficulty concentrating. Thirty-two respondents with a TBI reported both LOC and cognitive symptoms (43 %), significantly more when compared to six participants with cognitive symptoms without LOC (8 %) or 12 participants with LOC but no cognitive symptoms (15 %). Figure 5A demonstrates participants with previous TBI endorsing cognitive symptoms, LOC, or both.
The prevalence of cognitive symptoms following TBI in unhoused participants. (A) The percentage of participants reporting loss of consciousness (LOC) following TBI cross-analyzed with the percentage of participants reporting long-term cognitive symptoms following TBI. The highest percentage of study participants reported both LOC and cognitive symptoms following TBI. The “Unknown” column represent participants who did not disclose whether they had experienced LOC or cognitive symptoms following TBI. (B) The percentage of participants reporting long-term cognitive symptoms following TBI stratified into three housing groups. There was no statistically significant difference in the percentage of participants reporting long-term cognitive symptoms following TBI between housing groups.
Participants reporting cognitive symptoms following TBI included 23 of the 36 unsheltered participants (63.9 %), 16 of the 28 participants in low-barrier shelters (57.1 %), and 7 of the 11 participants in sheltered locations (63.6 %). The prevalence of cognitive symptoms was not significantly different based on housing strata (p=0.847). Figure 5B demonstrates those reporting cognitive symptoms categorized by housing strata.
Rates of cognitive symptom development following a TBI with LOC were compared, and no significant differences were found between the groups (p=0.589). The participants with a history of TBI and LOC included eight sheltered participants with TBI, with 50 % (n=4) endorsing cognitive symptoms. Seventeen participants in low-barrier shelters and 24 participants in unsheltered locations reported a TBI with LOC. Of those participants, 12 in low barrier shelters (70 %) and 16 in unsheltered locations (67 %) endorsed cognitive symptoms.
Of the 47 participants who endorsed cognitive symptoms, 10 (21 %) reported a single previous TBI, 13 (28 %) had two previous TBIs, and 21 (45 %) had three or more previous TBIs. Three participants (6 %) could not recall how many TBIs they had experienced. For those with cognitive symptoms, 31 (66 %) had experienced their first TBI more than 20 years ago; 5 (10.6 %) less than 1 year ago; 5 (10.6 %) 1–5 years ago; and 6 (13 %) 5–20 years ago.
Discussion
The primary goal of this study was to characterize the prevalence of TBIs in an unhoused population across various living conditions: shelters, low-barrier housing, and unsheltered locations within a single geographic area. This study examined an unhoused population seeking street medicine care from a small, Midwestern capital city. By sampling across housing strata within a single location, rather than exclusively looking at unsheltered homelessness, these results can be compared to similar existing studies of other housing strata. The present study found similar rates of TBI to those previously published for sheltered and low-barrier respondents, suggesting that the new data on unsheltered homelessness likely predicts similar rates in other, closely comparable cities.
Although it is possible to diagnose an acute TBI through neuropsychological testing and neuroimaging studies (computed tomography [CT], magnetic resonance imaging [MRI]), it should be noted that a mild TBI is expected to resolve completely or have subtle cognitive and behavioral sequelae; therefore, many diagnostic tools do not have the sensitivity required to measure these changes [29]. Given these diagnostic limitations, self-report remains the gold standard for assessing a history of TBI [30]. Therefore, an osteopathic physician needs to remain acutely aware of the interplay of body, mind, and spirit that is essential for conducting a focused history given that the physiologic recovery is not indicative of mental or spiritual resolution.
This study provides a critical next step in a concerning trend revealed by research: with each step away from stable housing, the prevalence of TBI increases. Ninety percent (90 %) of those experiencing unsheltered homelessness reported at least one previous TBI, with half reporting three or more TBIs. It is imperative that when interacting with patients who are currently experiencing or have previously experienced unsheltered homelessness, medical providers elevate their index of suspicion for TBI history and sequelae. Given the plurality of potential cognitive and neurovascular consequences of TBI [12], 31], increased vigilance among this population is warranted.
The secondary aims of this study included examining the prevalence of cognitive symptoms and LOC resulting from TBI. The relationship between repeated TBIs and cognitive deficits has been both supported [17] and questioned [32]. On one hand, the present study finds that those receiving three or more TBIs had a higher prevalence of cognitive deficits. On the other hand, the housing stratum with the most 3+ TBI respondents did not have a significantly higher prevalence of cognitive symptoms. There are several potential explanations for this apparent disparity, including: (1) that given how common both TBI and cognitive deficits are in all of the sampled strata, clear differences eluded observation in our binary, “yes” or “no” assessment; and (2) cognitive deficits can result from myriad causes including mental illness and substance use, both of which are more common among the sampled population and may confound attempts to establish a direct linear connection exclusively between TBI and cognition. Posttraumatic stress disorder (PTSD) and age-related cognitive decline are likewise known to impact cognitive function and underscore that the present results should be interpreted with caution.
In addition to repeated TBIs affecting cognition, the relationship between LOC and persistent cognitive symptoms has also been variously supported [33] and questioned [34], with more support for severe TBI affecting cognition than mild TBI [35], 36]. In the present study, nearly half of those reporting cognitive deficits also endorsed LOC after TBI. These results suggest the need for continued examination of chronic cognitive sequelae in both mild and severe TBI.
The rates of cognitive impairment are higher among individuals experiencing homelessness [37]. Any cognitive impairment increases the challenge of navigating the systems that exist to provide shelter, permanent supportive housing, vital documents, phone service, or healthcare [23]. A previous study demonstrated impaired cognitive functioning among those experiencing homelessness, with memory impairment in over half of the population sampled and 25 % with a reading level below fifth grade [38]. Additional assistance with resource navigation should be made available to those with a history of TBI. Data support the idea that the less housed a patient is, the more at risk the patient is; getting patients housed should therefore be prioritized to mitigate risk.
The role of TBI as cause or effect of homelessness remains unclear. Fifty-one percent (51 %) reported having their first TBI more than 20 years prior to sampling, which increases to 66 % when isolating respondents with cognitive symptoms. This is consistent with an earlier study that found that 70 % of sheltered respondents received their first TBI prior to the onset of homelessness [39]. The temporal relationship between an individual’s history of TBI and first unhoused experience remains unclear and should be examined in future studies. Given the role of adverse childhood experiences as contributing factors in developing homelessness [40], future studies should focus on assessing early-life TBI. Anecdotally, respondents in this study shared stories supporting TBI as both cause and effect. One respondent, a former college athlete, pointed to emotional disturbances that began after repeated head injuries on the field as a major contributing factor in his homelessness. Another described an unhealthy relationship formed out of necessity while living on the street as the cause of her TBIs. Intimate partner violence both before and after homelessness was a common theme and has been previously reported as a significant contributor to homelessness [41].
Strengths and limitations
This study captures data from a population of unsheltered homeless individuals, an unhoused population that has been historically underrepresented. Comparisons between unsheltered and sheltered homelessness were previously understudied terrain. The results of this study highlight the importance of treating unhoused populations as a heterogeneous population.
This study is not without limitations. While self-report measures may be relatively accurate within unhoused populations [42], we are examining a pathology with the ability to compromise memory and cognition. Throughout data collection, numerous respondents could not clearly recall when their injuries occurred, whether they lost consciousness at the time, and for how long they lost consciousness. Some respondents could not recall whether they had difficulties with memory.
This study does not include a housed control population, although it was previously demonstrated that significantly higher rates of TBI occur in an unhoused population as compared to housed, matched controls [43]. The participants represent a population that has proven difficult to engage due to the transient nature of unhoused populations and medical mistrust. Preexisting community partnerships and rapport with local encampments aided in the data collection. However, with individual transience, developing trust was often an insurmountable obstacle to participation. Furthermore, there are subsets of this population that student-led street medicine groups cannot interact with due to safety concerns for the volunteers (e.g., individuals exhibiting violent psychosis). However, many of these observed red-flag behaviors are consistent with a history of TBI. Factors to consider within this population are individual-level contributors to the housing status, including a higher prevalence of mental health disorders [44] and substance use, which may confound this data.
The study’s cross-sectional design, while considered an optimal approach to data collection due to concerns regarding participant medical mistrust and volunteer safety, did not permit the establishment of a temporal relationship between participant TBI and housing history. Additionally, the restriction of data collection to a single geographic area limits the ability to generalize the study’s findings to the broader unhoused population in the United States.
Conclusions
The results of this study demonstrate that individuals from a small Midwestern city who are the most marginalized experience a greater burden of TBI and repeated injuries. Future research is warranted to determine whether there is a definite causal relationship between TBI and homelessness. The osteopathic principle of rational treatment warrants examining whether housing interventions are effective in reducing the burden of neurocognitive sequelae caused by multiple, severe TBIs. Clinicians engaging with individuals with a history of housing insecurity need to elevate their index of suspicion for TBI sequelae when intervening in this patient population.
Acknowledgments
The authors wish to thank the City Rescue Mission of Lansing, the Projects for Assistance in Transition from Homelessness (PATH) team, Advent House Ministries, Homeless Angels, and Housing Services of Mid-Michigan for their assistance, as well as the Center for Statistical Training and Consulting (CSTAT) at Michigan State University.
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Research ethics: The study was reviewed by the Institutional Review Board at Michigan State University (IRB #00007783) and deemed exempt.
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Informed consent: All participants enrolled in this study participated in an informed consent process prior to study participation. Informed consent was obtained verbally and documented by a volunteer with the street medicine team trained in study protocols and procedures. Participants were not required to provide their name or any other personally identifiable information and were permitted to use a pseudonym, as is a common practice within the population of interest.
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Author contributions: The authors have accepted responsibility for the entire content of this manuscript and approved its submission.
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Use of Large Language Models, AI and Machine Learning Tools: None declared.
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Conflict of interest: None declared.
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Research funding: None declared.
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Data availability: The datasets generated and analyzed during the current study are available from the corresponding author on reasonable request.
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