Introduction

This review concerns itself primarily with task-sharing with non-specialist health workers (NSHWs), and associated concepts, to close the global mental health treatment gap. It seeks to integrate findings from different countries, contexts, and settings, seeking commonalities while respecting contextual differences that are historical, cultural, and system-based.

Mental disorders represent the greatest collective cause of disability globally today, yet a huge gap remains in treatment to meet the need [1]. Over the past decade, new methodologies and information has highlighted the rising prevalence and burden of mental disorders, with clear gaps separating the burden, spending on services, and available human resources, from actual service delivery [2,3,4,5,6,7,8]. An increased focus on cross-national planning and consensus-building on best practices mediated by the World Health Organization (WHO), and a growing discussion on universal health coverage in global health, has increasingly defined the need to innovate new models of care [9,10,11]. “Task sharing,” and the engagement of NSHWs in care, is a central lynchpin of this emerging work. This review draws from a body of literature in low- and middle-income countries in the field of global mental health, yet takes the perspective that, increasingly, the country of origin of the innovation matters less than the substance of the research and practice. The concepts of “open innovation,” “diffusion,” “flows,” or “counterflows” of innovation, and “reverse innovation,” encourage us to adapt new findings and varied experiences to the common goal of attaining equity in the availability and quality of mental health services across contexts [12,13,14,15,16,17,18].

In this review, we suggest several key approaches to implementation across high-, middle-, and low-income settings to facilitate task sharing with NSHWs as a service delivery strategy: “balanced care,” referring to a model of a linked system of services that is built on service delivery platforms; collaborative care, a model of a coordinated, integrated system of services designed to be person-centered; training methods, tools, supervision, and competencies that are designed, resourced, and innovated in order to meet significant and diverse educational and professional development needs for providers; use of trans-diagnostic approaches to developing psychosocial and psychological interventions that are problem-focused and dimensional or “staged” across provider cadres within a system; and the use of emerging digital technologies as a strategy to enhance various aspects of delivery.

Task Sharing

What Is This?

Task sharing in mental health involves the training of NSHWs—individuals with little or no prior formal training or background in mental health care—to deliver mental health care, including brief, low-intensity psychological treatments [19••, 20]. NSHWs include a broad range of health supporters and providers without specialized training and have been known by a variety of names in various contexts, including the following: community health workers (CHWs); lay health workers; midwives; nurses; primary care providers; village health workers; lady health workers; health promotores; auxiliary health staff; complementary alternative health providers; natural helpers; paraprofessionals; frontline health workers; teachers; religious and traditional healers; community members; and non-specialist providers [21]. Task sharing and CHWs have been critical to tremendous advances made in global health over the past two decades, with an emerging consensus of what can work best [22,23,24,25]. NSHW-based care has taken firm root in the delivery of care for HIV and maternal–child health in low-income settings, with applications to other chronic diseases, and to other contexts [26,27,28,29,30,31,32]. Taken together, increasing evidence on best practices in community health and increasing operational insights point to the importance of several factors in optimal functioning of NSHWs in general: payment; accreditation; being recognized and included in the health system; continuous training and modular or in-service learning; support from a dedicated supervisor; accessibility to services for service users; a proactive approach to active case finding; and monitoring and evaluation, with data feedback loops to improve care [33•]. Task sharing as a concept in mental health care delivery has existed as early as the 1970s, beginning with the notion of non-specialist delivery of psychotropic medications in global health [34].

Does Task Sharing Work?

Specific research focused on NSHWs delivering interventions has been primarily in low- and middle-income countries. Evidence for the effectiveness of task sharing in mental health care, and NSHW-delivered mental health support and care, exists across a continuum of roles and tasks, for a range of mental health-related problems and disorders, particularly for common mental disorders. Evidence for effective task sharing of psychosocial and psychological interventions to address the mental health treatment gap may be the most important research finding of the field of global mental health over the past decade [35]. This was supported by the evolution of the field of “global mental health” through a landmark Lancet series in 2007, launching “a new movement for mental health,” and subsequently followed with a 2011 Lancet series, a convening 2011 Nature publication, and a 2013 PLOS series on Grand Challenges in Global Mental Health [36,37,38,39,40,41,42,43,44,45,46,47]. Economic analyses associated with these initiatives have provided evidence that NSHW-delivered mental health care is cost-effective [48, 49, 50•, 51, 52]. Research hubs working across India, South Africa, Ethiopia, Uganda, Nepal, and elsewhere have together produced significant evidence regarding the clinical effectiveness, cost-effectiveness, and health system strengthening components of NSHW-delivered mental health care for a range of conditions [53,54,55,56,57,58]. A 2013 Cochrane analysis concluded that NSHWs are effective at delivering interventions in primary and community health care in low- and middle-income countries [59].

With regard to the care of common mental disorders, over the past 15 years, there has been a steady stream of important work on NSHW-delivered psychological interventions, with adaptation of evidence-based treatments including cognitive behavioral therapy (CBT) and interpersonal therapy (IPT) [60,61,62,63,64,65,66,67,68]. These findings have then been adapted to simplify and package interventions in ways that integrate core elements that are relevant in most contexts, particularly in resource-limited settings. Such new packaged interventions developed across sub-Saharan Africa and Asia and increasingly in South America include the Healthy Activity Program (for depression), based on behavioral activation; Problem Management Plus (for depression) and the Friendship Bench (for depression), based on problem solving therapy; and Thinking Healthy (for perinatal depression), based on CBT [69, 70, 71•, 72,73,74]. Innovation in research of psychosocial and psychological interventions is active and ongoing, with a range of problems and conditions being addressed, including severe mental illness, substance use disorders, childhood trauma in humanitarian settings, autism and disruptive behavior disorders, and depression in the elderly [75, 76•, 77,78,79,80]. A meta-analysis by Cuijpers et al. found that overall, psychotherapies for depression that are adapted to non-Western countries may be more effective when delivered in non-Western countries than in Western countries [81•]. This runs counter to the perception that psychotherapies may not be relevant or culturally adaptable to non-Western contexts. Based on several helpful reviews, we can expect that in global health NSHWs will also increasingly be engaged in evidence-based prevention and promotion activities in addition to clinical interventions [82, 83].

Although there is accumulating evidence to support task-sharing approaches to interventions for depression and other common mental disorders, there is less available research-based evidence about the nature and extent of task-shared care that is most effective for people living with severe mental disorders [59, 76•]. Hanlon provides a helpful review of the imperative to increase research on task sharing for severe mental disorders [76•].

How Has Task Sharing Been Used?

Based on the research evidence, the concept of engaging NSHWs to deliver simple clinical interventions is now commonly seen as the main alternative to lack of available mental health services in more resource-limited contexts. In 2011, WHO published an Intervention Guide (mhGAP-IG) for “mental, neurological and substance use disorders in nonspecialised health settings” based on extensive literature review and reflecting emerging international consensus on best clinical practices that can potentially be adapted to context by NSHWs, including generalist physicians [84]. A subsequent second edition was unveiled in 2016, and a similar guide developed specifically for use in humanitarian emergencies [85, 86]. These materials are increasingly being used by governments to decentralize mental health services to district hospital and primary care platform levels; however, beyond the sphere of research, the actual uptake of the practice of task sharing of mental health care by public health systems globally at a community platform level has been limited. Political will, funding, human resource capacity, and lack of consensus on what it is that NSHWs can do in delivering mental health care remain major challenges to achieving scale and access across the globe, including in high-income countries such as the USA [87, 88]. Task sharing of NSHWs is taking modest hold as a concept for mental health care delivery in higher-income contexts where health care disparities are significant, yet where NSHW roles are still being defined within existing health systems [89•, 90,91,92,93]. A recent review of the impact of CHWs on health care service use in the USA found a small number of studies on this topic. The review described variable effects of CHW interventions, that some may reduce costs and preventable utilization, and that reductions in care utilization and cost savings by integrating CHWs into chronic care management can be achieved [94•]. One existent promising example of mental health task sharing in the USA includes the emergence of psychiatric mental health nurse practitioners (NPs), covered by insurance, as a more cost-effective and scalable alternative to psychiatrists as medication prescribers, as well as associated efforts to expand coverage by NPs with psychological as well as pharmacologic treatments, as well as use of innovative training and use of technology [95,96,97]. As the evidence base for the effectiveness of mental health care by NSHWs has grown as evidenced by the global mental health literature, increased attention has been paid to various approaches needed for effective implementation of NSHW service delivery in higher-income settings. Barnett et al. have published several important reviews laying the groundwork for potentially deeper NSHW engagement on mental health care delivery in the US context, proposing a conceptual model of NSHWs that includes outreach and navigation, auxiliary care, stepped care, and providing care as a primary provider [98•, 99••].

Implementation Approaches to Facilitate Task Sharing

Balanced Care

The balanced care model is an evidence-based, systematic, but flexible approach to planning treatment and care for people living with mental disorders, describing mental health service components within a system. It can be adapted to account for human resource gaps that exist within countries, and it emphasizes the need for balance between different service delivery platforms and provider cadres [100••, 101]. The concept of care balanced across provider cadres within a linked system of services that is built on platforms of care and support can be helpful in defining system components and practices (see Fig. 1). The role of NSHWs within the framework should be informed by existing evidence on best practices in the functioning of NSHWs for other conditions. A key aspect of the balanced care model, and task sharing, is that there is a shared responsibility for care by specialist workers in the system (as distinguished from the concept of “task shifting”) [76•].

Fig. 1
figure 1

A balanced, systems-based mental health task sharing framework

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Consistent with global health system strengthening efforts for scaling community-based HIV care and maternal and child health care, mental health interventions of various kinds are also developed and delivered at various system and societal levels, called “platforms.” Essential platforms include specialist referral centers, general hospitals, primary health care centers, and emerging community services, which should include self-care and informal health care [101]. For each delivery channel, interventions may be categorized as promotion and primary prevention; identification and case detection; and treatment, care, and rehabilitation [102]. Digital technology can also be used to strengthen health systems and support key functions of these different platforms. The balanced care model also emphasizes the importance of evidence-based community and intersectoral interventions provided outside of the health care sector, such as employment opportunities, child protection services, measures to improve community-level understanding of mental disorders and increase the availability of long-term social care, and suicide prevention measures [100••, 103].

Collaborative Care

Collaborative care for chronic illness involves an integrated approach to addressing deficits in quality with patient self-management support, linkage to community resources, use of clinical information systems, provider decision support, and delivery system re-design [104]. Integrated care is defined as health services that are managed and delivered such that people receive a continuum of health promotion, disease prevention, diagnosis, treatment, disease management, rehabilitation, and palliative care services, coordinated across the different levels and sites of care within and beyond the health sector and, according to their needs, throughout the life course [105•]. The collaborative and integrated care movements have experienced a major global push over the past decade. Research related to stepped, collaborative care delivery models in depression care has shown the importance of specific key system components across platforms: population-based care for specific disorders that prioritizes screening, treatment and tracking of outcomes; self-care support, including family and patient education about illness and treatments, self-monitoring, and adherence support skills; care management and measurement-based care using patient-reported outcomes, focused on adherence, side effects, change in symptoms, and course of care following evidence-based guidelines; treatment to target and systematic monitoring of severity, with treatment intensification for patients not improving, according to evidence-based guidelines; case registry to track clinical outcomes (e.g., depression severity scores) and key process steps in order to facilitate transparent shared management across non-specialist workers, primary care providers and consulting specialists; psychiatric consultation for more complex presentations; and the use of proven clinical interventions, including brief psychological treatments and medications [106•]. A number of reviews summarize the need, and progress made, both in the USA and in global settings, in integrated, collaborative care for a range of mental health conditions [107,108,109,110,111,112]. An important finding is that a simple transfer of responsibility for psychiatric treatment to the existing primary health care settings is not enough to ensure an integrated treatment approach, and that task sharing will be necessary to ensure that there are enough qualified health care providers available [113•]. Strengthening of the primary care platform is essential. Another important aspect of a collaborative care model is prioritization of screening. Screening tools such as the Patient Health Questionnaire-9 are being increasingly used in higher-income settings and are also being adapted to more resource-limited settings for use by NSHWs. With regard to advances in detection and screening, ongoing work in global mental health is seeking to identify useful screens in resource-limited contexts that are culturally and contextually acceptable for identifying general and specific problems and concerns, such as dementia [114,115,116,117].

Sustaining Training and Supervision

Ongoing work in global health and in higher-income settings is seeking to improve our understanding of optimal training and supervision of NSHWs in provision of mental health care, with attention to core competencies [118,119,120,121,122,123, 124•]. Kohrt et al. have evaluated the roles, responsibilities, and practices of NSHWs delivering mental health care across 23 reviews [125••]. Kohrt et al. have also piloted a tool, the ENACT scale, to assess therapist competence in global mental health settings [126]. Training, supervision, competency assessment, and certification will be essential aspects of any successful task shared mental health system. The importance of a competency framework has been illustrated by one example of a successful scaled task shared model, the Improving Access to Psychological Treatments (IAPT) program in the UK [127•]. More than 537,000 patients with depression and anxiety have been treated annually through the training of NSHWs and specialists with brief accredited courses, with the progress of almost all (98%) patients assessed using a unique monitoring outcome system [20, 128]. The IAPT program uses task sharing combined with collaborative stepped care, to achieve clinical effectiveness, facilitate short wait times to improve patient attendance, and increase collaboration between providers and patients [20]. Underpinning this success is a robust training and supervision program [128].

Trans-diagnostic and Staged Interventions

The success of a balanced, collaborative system with robust training and supervision will be dependent on interventions that are simple enough to be utilized, and that are designed to address problems early. An effective integrated, task shared model for the mobilization of NSHWs in mental health support and care delivery will need to make functional a continuum of innovation and standardization that is systems- and context-specific, depending on the available work force and the tasks that are requested of NSHWs within the system (see Fig. 2).

Fig. 2
figure 2

An integrated, task shared model for the mobilization of NSHWs in mental health support and care delivery incorporates various key elements

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This continuum is predicated on a dimensional or staged approach to care that recognizes both trans-diagnostic as well as diagnostic approaches to identifying problems, based on the notion that the binary diagnostic system in mental health can at times falsely define “cases” and non-cases. A critique of the current system raises concern about missing problems and the opportunity to intervene early along a spectrum from wellness to distress to illness [129•]. A staged approach across wellness, distress, illness, and recurrent illness that integrates both a dimensional as well as a diagnostic approach recognizes opportunities for intervention at all stages of the pathway and is particularly useful in primary care, where people tend to present with less severe and more mixed symptoms compared with those in mental health services [100••]. This enables planners to identify specific skills for NSHWs across the care continuum. Specific interventions can include the following: mental health promotion, self-care, and community outreach activities to enhance wellness; psychoeducation, social support, addressing social determinants, screening for symptoms, and basic psychological strategies to support people in distress; basic support, brief and evidence-based psychological treatments, case management, follow-up, and referral for people living with illness; and psychological treatments, medication monitoring and adherence, minimization of institutional care, and referral to specialists for recurrent or refractory illness. At all dimensional levels of the continuum, resources should be committed to supervision and professional development of NSHWs to ensure quality and sustainability.

Ongoing research is leading to a more specific understanding of the most commonly utilized psychosocial and psychological elements in existing services. Singla et al. have evaluated the specific and non-specific elements used to address common mental disorders, developing a taxonomy of common elements used across 27 trials in low- and middle-income countries [19••]. Progress is also being made in clarifying transdiagnostic approaches (comprised of “core dysfunction,” “common elements,” and “principle-guided approaches”) to developing psychosocial and psychological interventions from empirically supported treatments [130•]. Ongoing research across high- and low-resource settings is currently clarifying the effectiveness and utility of “common elements treatment approaches” (CETA), which are an important key to understanding the potential sustained, “real-world” practice of NSHWs delivering psychological treatments [131,132,133,134]. Taken together, trans-diagnostic psychosocial and psychological interventions utilized within a balanced system, screening, and other tools and practices used in the collaborative care model, and sufficient NSHW training and supervision, could lead to a significant growth in access to care and services.

Digital Innovations

The use of digital technologies (i.e., mobile devices, smartphone applications, web platforms) can be applied to the following: screening, diagnosis, treatment, and care by NSHWs; training and supervision of NSHWs; health care and system-level improvement efforts including data management and enhanced care coordination across provider cadres; online therapies and self-directed care; peer support; social media and intervention; and reduction of stigma [100••]. Over the past decade, digital technologies ranging from mobile devices such as cell phones or smartphones to mobile applications, wearable devices, and online platforms have emerged as highly promising approaches both for supporting health care delivery and for the dissemination of psychological treatments [135,136,137,138, 139••]. For example, independent web-centered training can successfully train large numbers of therapists dispersed across a wide geographical area [140]. Technology should not replace the need for human interaction in the provision of care, but it can be designed to increase human connection and empower both lay workers and mental health professionals to more effectively support individuals and communities, as well as enhance individual self-help and provide the means through which individuals can help each other [141•]. Regarding NSHWs, mounting evidence shows that digital technologies can effectively support data collection, outcome tracking, health worker training, coordinating referrals, and improving communication between health workers and patients (see Fig. 3). Digital technologies can facilitate communication between NSHWs and the health system, their supervisors, and enable direct outreach and contact with patients, while empowering NSHWs by improving access to training and skill building opportunities, supporting clinical care and decision making, and facilitating data collection and monitoring for quality assurance.

Fig. 3
figure 3

Opportunities for digital technology to support NSHWs in delivering care

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However, there are fewer studies showing whether these digital strategies contribute to sustained improvements in clinical outcomes. Additionally, while the potential benefits of digital technologies for increasing capacity of NSHWs are well recognized, these strategies are not widely deployed as part of national health systems [142]. Furthermore, there are few studies that have leveraged digital technologies for supporting NSHWs in the delivery of evidence-based mental health care [139••]. There are an increasing number of studies using digital technologies for mental health care in low-resource settings, though much of this evidence is preliminary in nature, and few studies have focused specifically on supporting NSHWs. There has been a recent emergence of projects using digital interventions, such as text messaging, voice calls, web applications, and smartphones for supporting NSHWs with treating and preventing common mental disorders in primary care or community-based settings, responding to perinatal depression, and supporting care for persons living with schizophrenia [143,144,145,146,147,148,149]. In these examples, digital technologies were mainly used to enhance the role of NSHWs by providing access to training and continuing education opportunities, supporting data collection and care coordination, facilitating support for patients, and connecting with more specialized providers for supervision and clinical support. The digital technologies in these studies offer promise for supporting NSHWs in their roles and strengthening the delivery of existing evidence-based programs for mental health care.

Much of the research to date using digital technologies to support NSHWs in low-resource settings has involved preliminary pilot studies. This is partly attributed to a fragmented approach to conducting studies of digital interventions, where studies are often driven by exciting new digital innovations or donor priorities as opposed to planning ahead for implementation and scale up at a local or national level. There is also limited evidence on the effectiveness and cost-effectiveness of digital approaches, further highlighting the need for large-scale studies. Importantly, efforts are needed to explore the mechanisms of action for different interventions from a clinical perspective. This is essential, because digital technologies will continue to evolve rapidly over the coming years, potentially rendering current digital interventions obsolete. Therefore, only by understanding the mechanism of action, will it be possible to ensure that future digital interventions are designed based on proven principles as opposed to being dictated by the features of a new digital device or platform.

Additionally, the development and testing of digital interventions to support NSHWs in delivering mental health care must involve relevant stakeholders along every step of the development process. This includes stakeholders at the national government level, as well as the technology sector and in community settings as these diverse perspectives are critical for ensuring that efforts are guided by long-term goals to achieve sustainability. The input of various stakeholders is also relevant to the consideration of practical challenges related to interoperability of the digital systems and how these systems can integrate with existing care pathways to effectively support NSHWs in delivering mental health care. Use of digital technologies for mental health care delivery is still a nascent field, though continued cross-disciplinary and cross-national collaborations carry potential to substantively advance innovative models of NSHW-delivered mental health care.

Conclusions

A call is being made for psychiatrists globally to “think outside the box” [150]. This review highlights that a strong evidence base now exists for the effectiveness of task sharing in mental health services by NSHWs, particularly in low- and middle-income countries. The actual implementation of such services in a sustained, sensible way that is balanced across provider cadres, collaborative, simple enough to be implemented yet with safety and quality ensured through sufficient training and supervision, and inclusive of social determinants and wellness as well as illness, remains a substantial challenge to health systems across all contexts. Despite the promise of digital technologies for supporting NSHWs, there are many gaps in the literature. The significant global treatment gap persists, and more work remains. The field of global mental health, with an increasing emphasis on implementation- and practice-based research, is increasingly merging with like efforts in psychiatric services, community health, nursing, social work, psychology, mobile and digital health, medical informatics, and other disciplines to advance shared objectives and learning [151, 152•]. Increasingly, collaborative efforts across disciplines can counter divergent or even contradictory views on the topic within the field of mental health, for example, related to concerns held by established mental health professionals that they could lose professional identity and power or that clinical standards might be compromised through the adoption of task shared models of care [100••]. More specificity from research about how to solve specific implementation challenges will inform policy gaps to increase resources and services [153]. Achieving greater efficacy, efficiency, acceptability, and sustainability of task shared interventions across contexts will require the ongoing commitment of program implementers and researchers, flexibility, and creativity across cadres of providers, committed participation of the associated professions of mental health and medicine, the engagement of policymakers and financiers, and the involvement of people living with mental disorders and other relevant stakeholders.