Highlights d Cities possess a consistent ''core'' set of non-human microbes d Urban microbiomes echo important features of cities and city-life d Antimicrobial resistance genes are widespread in cities d Cities contain many novel bacterial and viral species

CMAJ ResearchBackground: We sought to determine the lifetime prevalence of traumatic brain injury and its association with current health conditions in a representative sample of homeless people in Toronto, Ontario. Methods:We surveyed 601 men and 303 women at homeless shelters and meal programs in 2004-2005 (response rate 76%). We defined traumatic brain injury as any self-reported head injury that left the person dazed, confused, disoriented or unconscious. Injuries resulting in unconsciousness lasting 30 minutes or longer were defined as moderate or severe. We assessed mental health, alcohol and drug problems in the past 30 days using the Addiction Severity Index. Physical and mental health status was assessed using the SF-12 health survey. We examined associations between traumatic brain injury and health conditions. Results:The lifetime prevalence among homeless participants was 53% for any traumatic brain injury and 12% for moderate or severe traumatic brain injury. For 70% of respondents, their first traumatic brain injury occurred before the onset of homelessness. After adjustment for demographic characteristics and lifetime duration of homelessness, a history of moderate or severe traumatic brain injury was associated with significantly increased likelihood of seizures (odds ratio [OR] 3.2, 95% confidence interval [CI] 1.8 to 5.6), mental health problems (OR 2.5, 95% CI 1.5 to 4.1), drug problems (OR 1.6, 95% CI 1.1 to 2.5), poorer physical health status (-8.3 points, 95% CI -11.1 to -5.5) and poorer mental health status (-6.0 points, 95% CI -8.3 to -3.7).Interpretation: Prior traumatic brain injury is very common among homeless people and is associated with poorer health. Abstract

Objective-To comprehensively assess health care utilization in a population-based sample of homeless adults compared to matched controls under a system of universal health insurance. NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author ManuscriptMethods-Health care utilization was assessed for 1,165 homeless single adult men, single adult women, and adults in families and their age-and sex-matched low-income controls in Toronto, Canada from [2005][2006][2007][2008][2009]. Repeated measures general linear models (GLM) were used to calculate risk ratios and 95% confidence intervals.Results-Homeless participants had mean rates of 9.1 ambulatory care encounters (maximum=141.1), 2.0 emergency department encounters (maximum=104.9), 0.2 medical/ surgical hospitalizations (maximum=14.9), and 0.1 psychiatric hospitalizations per person-year (maximum=4.8). Rate ratios comparing homeless participants to matched controls were 1.76 (95% CI: 1.58-1.96) for ambulatory care encounters, 8.48 (95% CI: 6.72-10.70) for emergency department encounters, 4.22 (95% CI: 2.99-5.94) for medical/surgical hospitalizations, and 9.27 (95% CI: 4.42-19.43) for psychiatric hospitalizations.Conclusions-Within a system of universal health insurance, homeless people have substantially higher rates of emergency department and hospital use compared to general population controls. These differences are largely driven by the subset of homeless persons who are extremely high-intensity users of health services. KeywordsHealth care utilization; Homeless persons; Matched controls; Ambulatory care; Hospitalization Homelessness is a serious problem in North America. High rates of unemployment and mortgage foreclosures resulting from the recent global economic downturn have further perpetuated this crisis. 1 Approximately 650,000 people will experience homelessness each night in the United States, of whom over one-third are persons in families. 2 More than 1.6 million Americans spend at least one night in an emergency shelter or transitional housing each year. 2 In Toronto, Canada, more than 4,000 individuals experience homelessness on any given night, and approximately 27,000 people use emergency shelters each year. 3,4 Compared to the general population, homeless people have higher rates of chronic and acute health conditions and are at increased risk for all-cause mortality. [5][6][7][8] Despite their increased need for health services, homeless people are a marginalized population who frequently encounter barriers to accessing primary or preventative health care. 6,[9][10][11][12][13][14][15][16][17] In addition, they often face competing priorities for basic subsistence needs, 18 factors which may result in delays in health care seeking, deterioration in health status, unmet needs for care, increased mortality, and use of more expensive forms of health delivery. 6,11,[19][20][21] Evidence suggests that homeless people can be more intensive users of health services compared to the general population; 12, 22-26 yet, no comprehensive ass...