Youth comprise the fastest growing segment of people experiencing homelessness (PEH) in the United States (US) and Canada [1]. An estimated 4.2 million adolescents (aged 13–17 years) and young adults (aged 18–25 years) experience homelessness in the US each year, of which 700,000 experience homelessness as unaccompanied minors [2]. In Canada, 35,000–40,000 youth aged 13–24 years are estimated to experience homelessness or housing instability over the course of a year [3]. Pathways to youth homelessness emerge from individual and structural pressures, including histories of family conflict, abuse, economic stress, and involvement with child welfare or juvenile justice systems [2–4].

Among YEH populations, youth identifying as sexual or gender minorities (SGM), including lesbian, gay, bisexual, transgender, and queer identities, are overrepresented, and have a higher risk of experiencing homelessness in both the US and Canada [2, 3, 5]. For SGM youth in the US, the risk of homelessness is more than double that of their heterosexual and cisgender peers [5]. In Canada, SGM youth constitute an estimated 25%–40% of YEH, compared to only 5%–10% of the general population [6]. SGM youth face heightened risks of homelessness due to family rejection, eviction, or violence [7], and experience homelessness for longer durations compared to their heterosexual and cisgender peers [8].

YEH are more likely to intermingle with their housed peers, more likely to couch surf, and less likely to use homeless services [2–4]. These fluid and frequently changing living and sleeping arrangements make it challenging to characterize youth homelessness. The US Department of Housing and Urban Development (HUD) defines unsheltered homelessness as having a nighttime residence not designated for sleeping (eg, street, vehicle, or park), while sheltered homelessness includes staying in emergency shelters, transitional housing, and safe havens [9]. Federal US statutes like the McKinney-Vento Homelessness Assistance Act also include couch-surfing and doubling-up in the definition of homelessness, which are not mentioned in the HUD definition [10]. In Canada, YEH are defined as young people who live without parents or guardians and lack stable housing, and frequently described using terminology like, “homeless youth,” “street youth,” and “runaway youth” [3]. Variable definitions of “youth” by national agencies and other organizations further complicate defining YEH. The United Nations defines youth as people between the ages of 15 and 24 years [11], the National Conference of State Legislatures defines youth homelessness for individuals aged 13 to 25 years [12], and Canadian definitions of homeless youth include people between ages 13 and 24 years [13].

YEH face numerous challenges to their health, including from infectious disease. Sexually transmitted infections (STIs), bloodborne infections (BBIs), respiratory infections, gastrointestinal diseases, and vector-borne diseases are commonly diagnosed among PEH [14, 15]. Yet, as the risk factors of YEH may be dissimilar to both housed youth and older adults experiencing homelessness, so might be their infectious disease burden [1]. Youth that rely on couch-hopping, who sleep outdoors, or who access services in congregate shelters have different disease exposure profiles than their housed counterparts [1, 16]. For example, sleeping in crowded, poorly ventilated shelters increases the risk of respiratory diseases and other disease outbreaks [16]. Peer pressure among youth also substantially influences risk behaviors, like harmful drug and alcohol use, in ways that may not influence adults [17]. YEH are more likely to inject drugs, smoke cigarettes, and consume alcohol compared to housed youth, increasing potential exposure pathways for pathogens directly, such as through sharing or using discarded drugs or paraphernalia, or indirectly due to impaired decisions that influence other risk behaviors, like unprotected sex [17, 18]. YEH are more likely to have multiple sexual partners and engage in unprotected and transactional sex compared to their housed counterparts, increasing risks for STIs and BBIs [1, 19]. Furthermore, YEH face unique structural and social barriers to seeking or receiving clinical care, including difficulty finding appropriate services, limited transportation, and perceived stigma from providers [20]. Access barriers can result in more severe disease outcomes and potentially prolonged durations of homelessness, as illness and homelessness have a reciprocal effect on each other [20, 21].

YEH with multiple marginalized identities like SGM YEH experience heightened health inequities. SGM youth in general face increased infectious disease prevalence, namely from STIs, compared to non-SGM youth [22]. SGM YEH are more likely than cisgender and heterosexual YEH to report harmful substance use [23] and engage in risky sexual behaviors [24]. On average, SGM YEH are more likely than heterosexual and cisgender YEH to engage in sex with strangers [24], engage in unprotected sex [24], engage in survival sex [25], be a victim of sexual violence [24, 25], and use harmful drugs [26], increasing the risk of infectious disease exposure. All YEH—and especially SGM YEH—underutilize preventative health care services due to compounding structural and social barriers, including limited access to SGM-affirming care, negative perceptions of safety in service settings, and stigmatization of their SGM identity by health service providers [7, 27].

Previous reviews of infectious diseases among YEH published in the last decade to date describe burden from STIs and risk factors for STI exposure and acquisition [19, 28]. Several other reviews published prior to the last decade provide more comprehensive coverage of clinical concerns among YEH beyond STIs. These include reports of YEH’s disproportionate disease burden from STIs, respiratory infections like tuberculosis, and dermatologic infections and infestations like tinea, lice, and scabies, described further in Supplementary Material A [1, 29, 30]. However, these reviews may not provide a timely account of the infectious disease burden currently experienced by YEH. Thus, our narrative review aims to describe the landscape of available research and surveillance data enumerating infectious disease burden for YEH populations over approximately the last decade to date, while elevating existing gaps.

We present findings from peer-reviewed literature published between 2012 and 2020 that enumerate infectious diseases among YEH and SGM YEH in the United States or Canada (Table 1 and Table 2). The literature review followed a systematic search and screening process using keyword search strings, detailed in Supplementary Material B and C, and Supplementary Figure 1. We also introduce 3 national-level, publicly available surveillance datasets that quantify infectious diseases among YEH in the US or Canada (Table 3 and Supplementary Material D), and that may be leveraged in future analyses and surveillance of disease burden among YEH populations.

We conducted a literature search to identify peer-reviewed literature published in the United States or Canada over approximately the last decade to date that enumerate infectious diseases among YEH populations (Supplementary Material B and C). We identified 12 studies published between 2012 and 2020 covering locations across the United States and Canada (Supplementary Figure 1 and Table 1) that met our inclusion criteria (Supplementary Material B). Participant recruitment spanned different location types such as parks, neighborhoods, street outreach, and youth activity or resource centers. Housing terminology included “homeless” [32, 33, 40, 41], “street-involved youth” [31, 35–37], “street youth” [31, 34], “unstable housing” [39, 41], “transient youth” [38], and “runaway youth” [42]. The definition of youth also varied, with the lowest age for inclusion being 12 years, and the most common youngest age for inclusion being 14 years (n = 5). Conversely, the maximum age limit for inclusion ranged from 24 to 30 (Table 1). Most studies reported findings from both interview or survey data (eg, sociodemographic variables, risk behaviors), and biological testing data for disease detection [32–40].

Pathogens reported in the studies included human immunodeficiency virus (HIV; n = 7), hepatitis C virus (HCV; n = 5), hepatitis B virus (HBV; n = 1), Chlamydia trachomatis and Neisseria gonorrhoeae (n = 4), syphilis (n = 1), and unspecified STIs (n = 4) (Table 2). Prevalence was the most common measure of burden reported (n = 10). We found an even split between studies that assessed infectious disease burden as a primary outcome of their research [31, 34, 36, 37, 39, 42] and those that reported infectious diseases secondarily to behavioral outcomes, or in combination with risk behaviors (eg, sexual behaviors, drug use behaviors), socioeconomic status, or health care utilization [32, 35, 38, 40–42] (Table 2). Four studies reported a relationship between housing instability and STI and BBI detection [34, 38, 39, 42]. Others found that unstable housing operates through behaviors that increase risk for disease, like injection drug use and sexual risk behaviors [32, 33, 35, 37, 38, 40, 42]. Three studies enumerated infectious diseases among youth by both SGM identity and housing status [32, 34, 39]. One other study looked at the relationship between SGM identity to infectious disease risk among YEH but did not quantify disease burden [41]. Comparisons of infectious disease burden for youth by housing status (eg, sheltered vs unsheltered homelessness, or housed vs unhoused youth), or by SGM identity were missing in most of the reviewed studies.

As peer-reviewed literature enumerating the infectious disease burden for YEH over approximately the last decade remains limited, surveillance data may help fill this critical gap. The US Centers for Disease Control and Prevention (CDC) recommends integration of health and medical records with housing surveillance systems that enumerate PEH (eg, the United States or Canada’s Point-In-Time Counts) as a best practice for assessing infectious disease burden, as described in Mosites et al (2021) [46]. In addition, we identified 3 publicly available, national-level disease surveillance datasets that already stratify infectious disease rates by housing status and relevant youth age groups. These datasets include the CDC Online Tuberculosis Information System [44], which reports the incidence of tuberculosis cases for homeless US youth, the CDC Medical Monitoring Project [45], which includes HIV infection data among homeless US youth aged 18–24 years, and Canada’s Y-Track (formerly the E-SYS) [43], which includes STI and BBI prevalence among Canadian street youth. Currently, none of the surveillance systems identified here stratify infectious disease burden by both housing status and SGM identity, emphasizing a persistent dearth of data that characterizes infectious diseases among SGM YEH. These datasets are summarized in Table 3 and Supplementary Material D.

Overall, the studies describing infectious diseases among United States and Canadian YEH were too few to synthesize across and did not reflect the full range of infectious diseases this vulnerable population faces, emphasizing a major gap and need for further study. The overwhelming focus on BBIs and STIs aligns with previous findings that YEH experience disproportionate risk for diseases like HIV, HBV, HCV, C. trachomatis, and N. gonorrhoeae [1, 19, 29, 30] compared to the general youth population. However, there is a dearth of research exploring rates of other infectious diseases in this group. For example, little is known about respiratory diseases among YEH, although it is well known that adult PEH are at a higher risk of experiencing respiratory disease outbreaks, such as tuberculosis and COVID-19 [47, 48], from exposure in congregate settings and living in highly transient environments [1, 17]. Other diseases of concern among PEH in congregate settings include dermatologic infections, rhinoviruses, meningococcal disease, and rare infections like Bartonella quintana (for which homelessness is a primary risk factor) [16], but these remain understudied among YEH.

There also remains a lack of data enumerating infectious diseases among SGM YEH, even though SGM youth are overrepresented among YEH and experience heightened infectious disease risk factors compared to non-SGM YEH [2, 5, 8, 25–27]. Furthermore, small sample sizes, narrow geographic scope, and insufficient comparison data on infectious disease burden among counterfactual youth populations hindered us from assessing differential vulnerability or exposure to infectious diseases among YEH and SGM YEH. Small sample sizes and lack of counterfactual data in the studies constrained our ability to explore relationships between infectious disease burden and other salient demographic variables, like race and ethnicity. Overlapping marginalization, such as those based on one’s SGM identity, housing status, race, or ethnicity can independently influence access to homeless services and care-seeking behaviors [20], and together may have a modifying effect on infectious disease risk among YEH [21]. Thus, our review emphasizes the need for additional studies examining infectious disease rates among YEH along sociodemographic lines. Finally, findings were limited by the predominantly urban settings of the studies covered in this review (Table 2). Homelessness research is overwhelmingly conducted in urban locations, which may not adequately represent the demographics, living situations, and health conditions of YEH in rural and nonurban areas [2].

Most study types were limited to secondary analyses of cohort studies (Table 1) [31, 34, 35, 36, 38, 39, 41, 42], which employ outreach at youth centers, housing service sites, and other community locations where YEH reside. Secondary analyses are valuable when quantifying the health outcomes of people who may not be easily identifiable. However, YEH often underutilize shelters, are transient, and sleep in locations different from those occupied by adult PEH [2–4], so these approaches may miss substantial portions of YEH populations. Diversified mechanisms of primary data collection across urban and rural settings are needed, leveraging both survey data and biological sample testing to provide a more representative understanding of infectious disease burden among YEH.

Finally, inconsistent housing status definitions limited our ability to compare or aggregate rates of infectious diseases among YEH across studies. For example, the terms “street youth” and “street-involved youth” carry different connotations for housing stability and are not well-defined. “Homelessness” is also widely used but carries a broad range of definitions, even within social service and public health research. This is compounded by the inclusion of both Canadian and US study locations, across which standard housing status descriptors are not employed.

While current literature may fall short of enumerating infectious disease rates among YEH, surveillance data can be used to assess burden from certain infectious diseases (Table 3). However, housing status is often inconsistently collected or reported in health surveillance and electronic health record systems [46], despite being a major social determinant of health, adding to the challenge of enumerating diseases among YEH. Where it is reported, careful consideration of definitions of homelessness and youth used by the surveillance systems should be taken when calculating and reporting measures of disease burden [46, 49]. Our review echoes the call for more standardized collection of housing status and sociodemographic variables (eg, SGM identity) in public health surveillance data, which would facilitate effective outbreak assessment and tailored interventions that prevent adverse health outcomes from infectious diseases among YEH.

Limitations of our review methodology include the possibility that our search terms missed some of the literature relevant to this topic, population, geography, and time (Supplementary Material E). Additionally, there may be local-level surveillance systems that enumerate infectious disease burden among YEH at smaller geographic scales that we did not identify for this review.

While YEH and SGM YEH may face increased risk for infectious diseases due to living circumstances and behaviors that differ from those of housed youth and older adults experiencing homelessness, their infectious disease burden remains understudied. Existing research suggests STIs and BBIs are of important concern among all YEH, but there is a dearth of literature on other types of infectious disease burden and risk. Surveillance data can aid in calculating and assessing burden from certain infectious diseases like STIs, BBIs, and tuberculosis among YEH. However, for enumerating other pathogens or diseases, integration of multiple data systems is recommended due to ongoing limitations in housing data completeness in health surveillance data. Standardized documentation of housing status and other demographic variables, like SGM identity, in disease surveillance systems, and more diversified sampling methods that include survey data and biological sample testing with a geographic catchment beyond urban areas will improve our understanding of infectious disease burden among YEH. Future infectious disease research should prioritize YEH and SGM YEH populations with better inclusivity of demographic variables in their disease burden assessment. Improved estimates of infectious disease burden among all YEH will support evidence-based interventions that protect the health of these vulnerable populations.