Introduction
Methicillin-resistant Staphylococcus aureus (MRSA) is a major antimicrobial-resistant (AMR) pathogen that poses a significant threat to both community and healthcare settings globally [Reference Murray1]. Current strategies for reducing MRSA infection and transmission have predominantly focused on healthcare settings; however, a critical gap remains in understanding and addressing the growing impact of community-acquired MRSA (CA-MRSA), particularly regarding the social determinants of disease and the need for tailored interventions. Although factors such as poverty, homelessness, and incarceration are well recognized, further research is needed to understand how evolving factors, such as changes in housing instability, mobility, and access to care, shape transmission dynamics and the effectiveness of interventions. Identifying these factors is crucial for optimizing public health interventions. This would reduce morbidity and mortality and enhance surveillance to better address the needs of vulnerable populations.
This disparity is particularly evident in socioeconomically disadvantaged communities, who bear a disproportionate burden of disease, particularly with CA-MRSA. Recent studies investigating CA-MRSA prevalence in North America have identified a nearly 25% incidence rate among people who inject drugs [Reference Parikh, Octaria and Kainer2], a 200% increased risk of colonization among individuals who have spent at least one night in a homeless shelter [Reference Leibler3], and colonization rates reaching 94% in incarcerated individuals [Reference Malcolm4] over the past decade. These high rates of colonization are likely influenced by common features of socioeconomically disadvantaged living conditions, such as limited access to sanitation, overcrowding, and insufficient hygiene resources, which Gill et al. [Reference Gill5] suggested may contribute to the ongoing transmission of CA-MRSA within these at-risk populations. The influence of these social determinants has been previously observed, as Gilbert et al. [Reference Gilbert6] highlighted their role in shaping health outcomes. Yet, CA-MRSA continues to pose a persistent challenge, with prevention efforts failing to adequately address the needs of high-risk groups. Current research on CA-MRSA in these populations is largely observational, and there is a notable lack of interventional studies addressing this pressing issue.
This scoping review examines trends related to CA-MRSA, focusing on the greater vulnerability of specific populations. It highlights key groups and associated risk factors that increase exposure to CA-MRSA, while also discussing the limitations of past research that have hindered effective mitigation efforts. The review emphasizes the necessity for expanded surveillance beyond primary care settings and calls for the development of tailored interventions to bridge resources to affected populations.
Methods
This scoping review was conducted in accordance with the PRISMA Extension for Scoping Reviews (PRISMA-ScR) guidelines [Reference Tricco7]. A comprehensive literature search was conducted using PubMed, MEDLINE, and Scopus, covering articles published from January 2000 to February 2024. The search combined terms for MRSA, including community-associated MRSA, social and economic vulnerabilities, and geographic location. MRSA-related terms included ‘MRSA’, ‘CA-MRSA’, ‘community-associated MRSA’, ‘community-acquired MRSA’, and variations of ‘methicillin-resistant S. aureus’, allowing for optional hyphenation and minor differences in wording. Vulnerability terms included ‘low socioeconomic status’, ‘low SES’, ‘poverty’, ‘homelessness’, ‘shelter*’, ‘injection drug use*’, ‘overcrowd*’, ‘unsanitary living conditions’, ‘sanitation’, ‘incarceration’, ‘jail’, and ‘prison’, with at least one vulnerability term required for inclusion. Geographic terms included ‘Canada’, ‘United States’, ‘USA’, ‘Mexico’, and ‘North America’. In PubMed and Scopus, these terms were combined using Boolean operators (AND, OR) to ensure that all articles addressing MRSA, including cases acquired or occurring outside healthcare settings among socially and economically vulnerable populations in North America were captured. For example, search combinations included (MRSA OR CA-MRSA) AND (‘low socioeconomic status’ OR poverty OR homelessness OR ‘injection drug use’) AND Canada or (MRSA OR CA-MRSA) AND (‘low SES’ OR poverty OR homelessness) AND ‘United States’.
Studies were included if they focused on North America, specifically encompassing Canada, the United States, and Mexico; however, no eligible studies from Mexico were identified at full-text review. Eligible studies addressed MRSA occurring or acquired outside healthcare settings among populations experiencing social and economic vulnerabilities, including poverty, homelessness, injection drug use, overcrowded or unsanitary living environments, and incarceration. The selection process included primary research, secondary research and case studies, while review articles were excluded, to ensure that only studies reporting original data on MRSA in the populations of interest were considered. Studies focusing exclusively on paediatric populations were excluded, although adult-focused studies may have included children. Studies were also excluded if all or the majority of data were collected prior to January 2000 or if they focused predominantly on laboratory-based molecular methods, infection control interventions, or other MRSA-related solutions without addressing the populations or conditions specified in the inclusion criteria.
Initial screening was conducted based on the title and abstract, assessing alignment with the inclusion and exclusion criteria. This process was carried out collectively by the review team (SCD, CG, NK, TM, and JLG). During the full-text screening phase, each article was independently reviewed by three investigators to ensure consistency with the established inclusion and exclusion criteria. In cases of discrepancies, a fourth investigator who had not previously reviewed the article, resolved the conflicts.
Results
The initial literature search produced 3,223 articles across PubMed, MEDLINE, and Scopus. After removing 477 duplicates, 2,746 articles remained for initial screening. The screening criteria resulted in the exclusion of 2,481 articles and a full-text review of the remaining 265 articles led to the inclusion of 40 relevant studies (Table 1), as depicted in the PRISMA flow diagram (Figure 1).
Table 1. Description of studies included in the scoping review
CA-MRSA, community-associated methicillin resistant S. aureus; EDs, emergency departments; PWID, people who inject drugs; SSTIs, skin and soft tissue infections.
Figure 1. PRISMA flow diagram of the scoping review process.
Risk factors associated with CA-MRSA among populations experiencing socioeconomic disadvantage
Across the studies, the prevalence of CA-MRSA was generally associated with socioeconomic disadvantage, related living conditions, and other social risk factors, although not all studies conducted formal comparative analyses [Reference Parikh, Octaria and Kainer2,Reference Leibler3,Reference Gill5,Reference Gilbert6,Reference Al-Rawahi8–Reference Moran43]. Key contributors to CA-MRSA transmission included factors such as overcrowding, poor sanitation, and limited access to clean water. For example, a population-based study in Brooklyn, New York (2005–2006) directly associated higher CA-MRSA prevalence with specific indicators of socioeconomic hardship: lower median household income, public assistance reliance, and overcrowded housing [Reference Bratu10]. Building on these findings, a 2017 longitudinal study further delineated risk factors prevalent in populations experiencing overcrowding, lack of personal hygiene, and limited access to clean facilities [Reference Leibler3]. This study highlighted that living in group settings, such as shelters, recent illicit drug use, regular contact with individuals in these environments, and constant use of public facilities significantly increased CA-MRSA risk [Reference Leibler3]. Similarly, in Canada, Gill et al. [Reference Gill5] reported that neighbourhoods in Calgary, Alberta with lower median income, higher proportions of visible minorities, and recent immigration had higher rates of CA-MRSA; specifically, for every $100,000 increase in neighbourhood income, the incidence of CA-MRSA decreased by 73%. Such predisposing factors are inherently tied to social determinants of health and environmental factors with poor sanitation and person–person contact acting as primary facilitators of transmission [Reference Lowy and Miller44,Reference Loewen45].
Reinforcing the association between living conditions and CA-MRSA, a prospective study conducted in Northwestern Ontario, Canada (2012–2013), examined 23 cases of CA-MRSA bacteraemia and found that inadequate living conditions and limited access to clean water significantly contributed to high rates of invasive infections [Reference Kirlew19]. Similarly, an analysis of MRSA surveillance data in the United States suggested that the disproportionate impact of CA-MRSA could be attributed to behaviours and factors associated with socioeconomic disadvantage, specifically injection drug use, prior incarceration, and crowded living conditions [Reference See26]. These converging findings underscore the significant role of social determinants of health, including homelessness, substance use, and incarceration, in amplifying CA-MRSA risk among vulnerable populations. Additionally, limited access to healthcare and community resources may further exacerbate CA-MRSA occurrence in these groups. For example, a study in California [Reference Morgan Bustamante16] found that area-level poverty was associated with increased CA-MRSA cases, suggesting that structural barriers, including access to clean facilities, preventive care, and community health services, can amplify transmission risk in disadvantaged settings.
Incarceration and CA-MRSA risk
Eleven of the 40 studies reviewed identified an association between CA-MRSA colonization or infection and incarceration [Reference Gilbert6,Reference Bratu10–Reference Farley12,Reference Leibler14,Reference Lowy15,Reference Gilbert18,Reference Main22,Reference Elias34,Reference Mullen and O’Keefe36,Reference Mukherjee38]. This association reflects the unique risk factors present in correctional facilities, such as overcrowding, inadequate sanitation and hygiene conditions, and frequent close contact. Further illustrating these dynamics, a study from Ontario, Canada, investigated two outbreaks of CA-MRSA skin and soft tissue infections that occurred in a correctional facility in 2002 and 2004 [Reference Main22]. The study revealed that half of the infected inmates were housed in the same cellblock as another inmate colonized with CA-MRSA [Reference Main22], demonstrating an increased risk of acquiring and transmitting CA-MRSA within correctional environments. The investigators identified past or present incarceration within the Canadian penal system as the primary risk factor for infection [Reference Main22].
Further exploring this connection, a study conducted in Baltimore, Maryland, in 2006 examined the prevalence and risk factors of S. aureus colonization among newly arrested men through nasal swabs and molecular characterization of isolates [Reference Farley12]. Overall, 40.4% (243/602) were colonized with S. aureus, and 15.8% (95/602) were colonized with MRSA, with 80% of these MRSA strains identified as USA300 or related subtypes of CA-MRSA [Reference Farley12], a highly virulent community strain. The findings indicated that MRSA colonization, particularly the USA300 strain, was significantly higher in this population compared to the general public. While residing in correctional facilities indicated a greater likelihood of MRSA infection, a prior arrest history alone did not significantly elevate MRSA prevalence [Reference Farley12]. Incarceration, emerged as a stark example of how institutional conditions, such as those previously listed, exacerbate the risk. This points to the need for targeted interventions within these settings and for individuals transitioning back into the community, ensuring that risks are mitigated not only during incarceration but also after release to prevent transmission to the broader population.
Persons who inject drugs
Injection drug use was identified as a significant risk factor for CA-MRSA in 22 of the articles reviewed [Reference Parikh, Octaria and Kainer2,Reference Leibler3,Reference Gilbert6,Reference Al-Rawahi8,Reference Al-Rawahi9,Reference Kreisel13,Reference Leibler14,Reference Gilbert18–Reference Main22,Reference Nourbakhsh24,Reference Stenstrom28–Reference Agusto and Kim33,Reference Jackson39–Reference Lorson, Heidel and Shorman41]. An analysis of data from seven of these studies showed that, on average, 20% of persons who inject drugs (PWIDs) were found to be colonized with CA-MRSA, with the prevalence ranging from 8% to 27% [Reference Parikh, Octaria and Kainer2,Reference Al-Rawahi8,Reference Al-Rawahi9,Reference Kirlew19–Reference Lloyd-Smith21,Reference Nourbakhsh24]. Furthermore, data from the U.S. CDC’s Emerging Infections Program, a national surveillance program, revealed that PWIDs are 16 times more likely to become infected with MRSA compared to the general population [Reference Parikh, Octaria and Kainer2]. In Vancouver, Canada, CA-MRSA prevalence among hospitalized PWID rose considerably from 4% in 2003 to 27% in 2005, with 45% of all identified cases associated with this group [Reference Al-Rawahi8]. Similarly, a study in Tennessee, USA, documented a rapid rise in CA-MRSA cases among PWID, increasing from 16.1% in 2015 to 29.9% in 2017 [Reference Parikh, Octaria and Kainer2]. Additionally, a multicentre study conducted at four Veteran Affairs medical centres in the United States found that CA-MRSA infection was most prevalent among illicit drug users, 59% of whom were PWID, compared to those who did not use illicit drugs [Reference Kreisel13]. It is important to note that while the prevalence of MRSA among illicit drug users decreased over the study period, it increased in non-illicit drug users, indicating a broad spread within the veteran population [Reference Kreisel13]. Taken together, these studies highlight PWID as a population at higher risk of acquiring and potentially spreading CA-MRSA, particularly through skin and soft tissue infections.
Homelessness and CA-MRSA in North America
Of the 40 articles included in this review, nine reported that persons experiencing homelessness are at a higher risk of acquiring and transmitting CA-MRSA [Reference Leibler3,Reference Gill5,Reference Gilbert6,Reference Leibler14,Reference Gilbert18,Reference Nourbakhsh24,Reference Ottomeyer25,Reference Szakacs29,Reference Young32]. Congregate settings more broadly have also been associated with MRSA transmission. For example, Szakacs et al. [Reference Szakacs29] found that among 40 inner-city shelter staff and 44 residents, MRSA colonization was 0% and 4.5%, respectively, demonstrating the potential for transmission in settings where people live closely together.
Studies examining mobility and shelter use identified additional risk factors. A cross-sectional study at a Boston health clinic serving unhoused persons found that 75% of the study population were colonized with the CA-MRSA USA300 strain [Reference Leibler14]. Individuals who slept in more than one location per week had a 40% increased risk of MRSA colonization, and those who spent at least one night in a shelter within the prior 3 months were more likely to be colonized (P = 0.02) [Reference Leibler14]. A subsequent a study focusing on PWID in Boston further showed that sleeping in multiple locations in a week was strongly associated with MRSA colonization (P = 0.01) [Reference Leibler3], and spending even a single night in shelter over a 90-day period was associated with a 200% increase in MRSA colonization (OR 3.0; P = 0.02; 95% CI 1.2–7.62) [Reference Leibler3].
In Canada, a retrospective study conducted in Calgary, Alberta, from 2004 to 2014, also observed an increase in CA-MRSA prevalence, with the proportion attributable to CA-MRSA strains rising to 52% over the decade [Reference Gill5]. This study identified ‘transmission hotspots’ in Calgary’s downtown region, particularly in areas with high concentrations of shelters serving people experiencing homelessness and individuals affected by substance use disorders [Reference Gill5]. These hotspots were characterized by high population density and limited access to hygiene facilities. These studies clearly demonstrate that people experiencing homelessness have an increased vulnerability to CA-MRSA acquisition.
Discussion
Our scoping review findings indicate that CA-MRSA places a heightened burden on several high-risk populations in North America, including individuals experiencing socioeconomic disadvantage, homelessness, incarceration, or drug use, and others living in poor conditions [Reference Gill5,Reference Gilbert6,Reference Young32]. Studies from Canada and the United States consistently report significantly higher CA-MRSA occurrence among these groups [Reference Gill5,Reference Main22,Reference Szakacs29,Reference Vayalumkal30,Reference Young32]. Although studies examining CA-MRSA in these populations exist, relatively few provide comparative data across settings, and study quality and scope are variable. Consistent with the purpose of a scoping review, our aim was to map existing evidence and identify knowledge gaps, rather than conduct a comparative analysis.
Across the studies reviewed, several report high colonization rates. For example, MRSA colonization among newly arrested men in Baltimore was 15.8%, markedly higher than the general population [Reference Farley12], and colonization among shelter residents ranged from 4.5% to 75% depending on setting and population [Reference Leibler3,Reference Leibler14,Reference Szakacs29]. These populations share common risk factors, such as close living quarters, limited access to hygiene facilities, inadequate sanitization, and exposure to potentially contaminated environments and objects [Reference Gill5]. These overlapping risk factors create environments conducive to CA-MRSA transmission. While research over the past two decades has identified the significant burden of CA-MRSA on these communities, gaps remain in fully understanding the intricacies of its impact and implementing effective prevention and control measures, such as community-based hygiene education and rapid testing initiatives.
Low socioeconomic status and poor living conditions exacerbate the risk of acquiring CA-MRSA
CA-MRSA infection and transmission in high-risk groups are predominantly associated with socioeconomic factors such as poverty and poor living conditions across the literature [Reference Parikh, Octaria and Kainer2,Reference Leibler3,Reference Gill5,Reference Gilbert6,Reference Al-Rawahi8–Reference Moran43]. Several densely populated North American cities exhibited increased CA-MRSA prevalence, driven by substandard living conditions, including poor sanitation, overcrowding, and inadequate access to clean water [Reference Bratu10,Reference Kirlew19]. These predisposing factors are intrinsically associated with the social determinants of health affecting low socioeconomic status (SES) populations in North America [Reference Bratu10]. Since the early 2000s, studies have identified low SES as a critical driver of CA-MRSA persistence and spread. Subpopulations examined in this review often experience the overlapping challenges that reinforce the cyclical nature of the CA-MRSA crisis [Reference See26]. Without targeted intervention programs, SES will continue to exert a significant influence on the health outcomes of vulnerable populations facing CA-MRSA in North America.
Incarceration increases the likelihood of CA-MRSA infection
Our review identifies shared mechanisms by which living conditions and incarceration promote further CA-MRSA infection and transmission. Correctional facilities are characterized by overcrowding and close living quarters, conditions that facilitate the spread of CA-MRSA [Reference Farley12]. However, research on how incarceration contributes to the broader community spread of CA-MRSA remains limited. The entry of newly arrested individuals into an environment where long-term inmates are already colonized with CA-MRSA can sustain outbreaks, further perpetuating transmission within the facility [Reference Farley12,Reference Lowy15]. Inadequate medical screening and lack of preventive measures exacerbate the risk, allowing correctional facilities to serve as reservoirs for CA-MRSA spread within incarcerated populations [Reference Gilbert6,Reference Farley12,Reference Main22]. Notably, early outbreaks of CA-MRSA were observed in jail populations, suggesting that incarceration settings may have been key focal points for the pathogen’s initial spread into the community [46]. Collectively, these findings demonstrate the need for further research and surveillance to better understand the spread of CA-MRSA within correctional facilities, which may facilitate transmission both within this vulnerable population and into the broader community.
Injection drug use and CA-MRSA risk
Injection drug use is increasingly recognized as a significant factor in the spread of CA-MRSA. Studies, including those by the Centers for Disease Control’s Emerging Infections Program, have shown that PWID are at significantly higher risk for MRSA infection [Reference Parikh, Octaria and Kainer2]. Colonization rates among PWID have been reported as high as 75% for USA300 CA-MRSA strains in unhoused populations [Reference Kreisel13]. This elevated risk is driven by several factors, such as skin damage from repeated injections, needle sharing, and immunosuppression due to drug use [Reference Leibler3,Reference Leibler14,Reference Gilbert18]. The repetitive nature of drug use further compounds the risk, as PWIDs are more likely to carry and transmit MRSA, increasing the potential for widespread infection within this population [Reference Kreisel13]. Furthermore, the environments associated with illicit drug use, from crowded shelters to abandoned buildings or outdoor spaces, can facilitate CA-MRSA exposure and spread. In these settings, the urgency of quick administration often outweighs hygienic practices, increasing infection risk for PWIDs [Reference Grant47]. Despite this, MRSA surveillance efforts remain primarily focused on hospital settings, which may not accurately capture the extent of infection within high-risk community environments [Reference Al-Rawahi8,Reference Al-Rawahi9,Reference Achiam17,Reference Stenstrom28,48,49]. Broadening surveillance and active case finding to include shelters and supervised injection sites would provide critical insights and support the development of targeted harm reduction strategies to mitigate transmission and prevent outbreaks.
Homelessness as a risk factor for CA-MRSA infection
Individuals experiencing homelessness often face limited access to hygiene products and services, compounded by frequent use of communal spaces such as shelters, washrooms, and beds which increase the likelihood of bacterial colonization and transmission [Reference Leibler3]. Studies have shown that even a single night in a shelter can double or triple the risk of MRSA colonization [Reference Leibler3,Reference Leibler14,Reference Szakacs29]. Mobility between multiple sleeping locations further increases exposure risk. Given the frequent use and overcrowding in these spaces, maintaining cleanliness is crucial to preventing the spread of CA-MRSA. Furthermore, shelters have the potential to act as surveillance points for CA-MRSA in the community. Previous studies have used locations such as community health centres in areas with high populations of unhoused individuals for data collection, given the presence of relevant groups in these settings [Reference Al-Rawahi8,Reference Stenstrom28,Reference Oudshoorn50]. Similarly, monitoring CA-MRSA prevalence in shelter environments could provide more accurate epidemiological data on at-risk populations, enabling better-targeted interventions and resource allocation.
Limitations
Much of the existing MRSA surveillance and research has focused on hospital settings, which may not fully capture transmission dynamics in broader community contexts. Reliance on hospital-based data can obscure community hotspots and fail to adequately capture vulnerable populations. Studies that include emergency department samples may introduce sampling bias, as disadvantaged populations often rely on the Emergency Department as their primary point of care, potentially inflating infection severity. Certain regions, such as Mexico, remain largely unexamined in the literature, limiting our understanding of CA-MRSA dynamics and restricting the development of region-specific interventions. While this review identifies key populations at risk, other vulnerable groups, such as migrant workers in agricultural settings who experience overcrowding and limited access to healthcare, have not been adequately studied. These gaps highlight the need for research in underexamined regions and additional high-risk populations.
Conclusions
CA-MRSA remains a significant public health concern, disproportionately affecting populations facing socioeconomic disadvantage, incarceration, homelessness, or injection drug use. Shared risk factors, such as close living quarters, limited access to hygiene facilities, insufficient sanitization, and exposure to potentially contaminated environments, facilitate transmission. As North America faces rising poverty, homelessness, and substance use, these intersecting risk factors amplify CA-MRSA transmission. A holistic approach is needed to protect both high-risk populations and the broader community, including expanded surveillance, targeted interventions, and innovative methods such as genomic epidemiology to identify transmission clusters. Addressing social determinants of health alongside these strategies will be essential to reduce CA-MRSA transmission and mitigate its impact across society.
Data availability statement
All data supporting the findings of this scoping review are derived from publicly available published literature.
Author contribution
Formal analysis: CG, NK, SCD, TM; Conceptualization: CG, NK, SCD, TM, and JLG; Writing—original draft: CG, NK, SCD, TM, and JLG; Writing—review & editing: CG, NK, SCD, TM, and JLG; Supervision: JLG; Project administration: JLG.
Funding statement
This work was supported by the Canadian Institutes of Health Research Project Grant awarded to JLG, who is also supported by the Canada Research Chairs Program.
Competing interests
The authors declare that they have no conflicts of interest.
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