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Approaches and outcomes of community health worker’s interventions for hypertension management and control in low-income and middle-income countries: systematic review

Objectives To critically appraise the scope, content and outcomes of community health worker (CHW) interventions designed to reduce blood pressure (BP) in low-income and middle-income countries (LMICs). Method We performed a database search (PUBMED, EMBASE, CINAHL, PsycINFO, OpenGrey, Cochrane Central Trials Register and Cochrane Database of Systematic Reviews) to identify studies in LMICs from 2000 to 2020. Eligible studies were interventional studies published in English and reporting CHW interventions for management of BP in LMICs. Two independent reviewers screened the titles, abstracts and full texts of publications for eligibility and inclusion. Relevant information was extracted from these studies using a tailored template. Risk of bias was assessed using the Cochrane collaboration risk of bias tool. Qualitative synthesis of results was done through general summary of the characteristics and findings of each study. We also analysed the patterns of interventions and their outcomes across the studies. Results were presented in form of narrative and tables. Results Of the 1557 articles identified, 14 met the predefined criteria. Of these, 12 were cluster randomised trials whereas two were pretest/post-test studies. The CHW interventions were mainly community-based and focused on behaviour change for promoting BP control among hypertensive patients as well as healthy individuals. The interventions had positive effects in the BP reduction, linkage to care, treatment adherence and in reducing cardivascular-disease risk level. Discussion and conclusion The current review is limited in that, a meta-analysis to show the overall effect of CHW interventions in the management of hypertension was not possible due to the diversity of the interventions, and outcomes of the studies included in the review. Summarised outcomes of individual studies showed CHW enhanced the control and management of hypertension. Further studies are needed to indicate the impact and cost-effectiveness of CHW-led interventions in the control and management of hypertension in LMICs.


INTRODUCTION
Globally, hypertension is a leading modifiable risk factor for cardiovascular disease (CVD) and premature death, 1 2 with an estimated 1.13 billion people worldwide living with it. Two-thirds of this burdened population live in low-income and middle-income countries (LMICs). 3 The WHO targets to have a worldwide 25% reduction in the prevalence of hypertension by the year 2025. 4 Due to an ageing population and increase in lifestyle risk factors such as lack of physical activity, unhealthy diet, smoking and alcohol consumption, the global prevalence of hypertension is increasing. 2 However, there are disparities in these changes of prevalence of hypertension worldwide. While high-income countries experienced a modest decrease (2.6%) in hypertension prevalence in the last two decades, the LMICs experienced significant increase of 7.7%. 5 The proportion of controlled hypertension is also low, especially in LMICs with only 7.7% of patients with hypertension having controlled blood Strengths and limitations of this study ► This is the first systematic review with focus on approaches and outcomes of community health worker (CHW) interventions in the management and prevention of hypertension in low-income and middle-income countries. ► We conducted a comprehensive search of databases to ensure that all the relevant publications were identified. ► Potential bias in the conduction of this review was minimised by having the authors independently screen the search results and extract the data autonomously. ► Due to diversity of the study participants, interventions and outcomes of the studies included in the review, a quantitative synthesis (meta-analysis) to show the overall effect of CHW interventions was not possible and therefore this review has reported summarised outcomes for individual studies.
Open access pressure (BP) (<140/90 mm Hg) in LMICs. 5 Concerted efforts are urgently needed to combat the emerging hypertension burden in LMICs. Health workers are critical to addressing this emerging burden. In light of critical shortages in the health workforce in LMICs, community health workers (CHWs) are increasingly recognised as an essential part of the health workforce needed to achieve public health goals. [6][7][8][9][10] However, the concept of CHWs has no universal definition and has evolved to suit specific contexts, norms and cultures. 11 In their systematic review 'Who is a Community Health Worker?' 11 Olaniran et al concluded that a single definition may not project the diversity of this group of health workers and emphasised that these are 'individuals with an in-depth understanding of the community culture and language, have received standardised job-related training which is of shorter duration than health professionals, and have a primary goal of providing culturally appropriate health services to the community'. 11 In this review a CHW will refer to 'lay health worker carrying out functions related to healthcare delivery; trained in some way in the context of the intervention and having no formal professional or paraprofessional certificate or degree in tertiary education'. 12 Use of CHWs has been identified as an important strategy in the delivery of culturally relevant programmes for hypertension control in different settings. The CHWs approach is not only affordable and sustainable but also enhances cultural relevance of health information, providing an important linkage between community and healthcare system. 13 Previously, systematic reviews have assessed the effectiveness of CHW community-based programmes in the management and prevention of non-communicable diseases (NCDs) 7 14-16 but few have focused on the care of people with hypertension specifically. 17 18 Evidence from systematic reviews of community-based randomised controlled trials (RCTs) and cluster randomised trials from LMICs show that CHWs are effective in altering the risk factors for NCDs and demonstrated their effectiveness in modification of physical parameters such as BP and cholesterol levels. 7 Although CHW delivered community-based BP screening and education initiatives are recommended for management and prevention of hypertension in LMIC, 19 there are few systematic reviews focused in this area. Reviews have demonstrated the effectiveness of training programmes for CHW 20 and task-sharing with non-physician health workers 21 in the management of hypertension in LMICs. Similarly, in their systematic review examining implementation strategies for the control of BP, 22 Mills et al found that multilevel and multicomponent strategies such as team-based care involving non-physician healthcare workers 23 were the most effective in the management of hypertension. The purpose of this systematic review was to critically appraise the scope, content and outcomes of CHW interventions designed to reduce BP in LMICs.

Review question/objective
The objective of this systematic review was to identify studies reporting on CHW interventions for hypertension management and control and determine the approaches and outcomes of such interventions in LMICs. Specifically, we asked: (1) what are the types of CHW interventions in the management and control of BP in LMICs and (2) what are the outcomes of CHW interventions on the management and control of BP in LMICs?

METHODS
We carried out a systematic review of literature and a descriptive review of studies reporting CHW interventions for hypertension management and control. The review followed the recommended methodological framework of conducting a systematic review of healthcare interventions 24 and the reporting adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 guidelines for reporting such reviews. 25

Eligibility criteria
We identified peer-reviewed literature-RCTs, quasiexperimental and pretest/posttest studies published between January 2000 and September 2020. We included studies that were available in English language and focused on the management and control of high BP among adult population in LMICs.

Inclusion criteria
Studies were included in the analysis if they met the following; Population: Studies focusing on management or control of BP among the general population or among pre-hypertensive or hypertensive patients.
Intervention: CHW interventions focused on management and control of hypertension. In the current study, CHW referred to a lay health worker who is not formally and professionally trained, either paid or working on voluntary basis, and carrying out functions associated with healthcare delivery in the management and control of hypertension.
Comparison: Studies had a comparison control arm of either no intervention, usual care or another intervention. However, pretest/post-test studies with a welldefined intervention were also included.
Outcomes: Reduction in BP, proportion of patients with controlled BP, engagement in hypertension care, adherence to hypertensive drugs and reduction in cardiovascular risk.
Study designs: RCTs, quasi experimental and pretest/ post-test studies were included.
Setting: Only studies conducted in LMICs (as defined by the World bank) were included.

Exclusion criteria
Studies whose intervention was not adequately described or whose outcomes were not clearly described were excluded from this analysis.

Information sources
We searched for relevant studies in electronic databases: PUBMED, EMBASE, CINAHL, PsycINFO, OpenGrey, Cochrane Central Trials Register and Cochrane Database of Systematic Reviews. This comprehensive search was needful to identify interventional studies meeting the eligibility criteria in LMICs.

Search strategy
The relevant studies were identified using different search strategies. The basic search string used towards this review was "Community Health Workers"[Mesh] OR "community health volunteers" OR "lay health workers") AND "Hyper-

Study selection
We employed Covidence, an online software (Covidence, Roende, Denmark) to extract and screen for articles to be included in the study. The inclusion criteria described above informed the study selection. Two reviewers (GM and KM) assessed all retrieved lists of citations and abstracts independently. The full texts of all potentially eligible studies were retrieved and critically examined to ensure they met all the inclusion criteria. Discrepancies between reviewers about the eligibility of retrieved studies were resolved by discussion. The reference lists of the selected publications were also searched for identification of additional studies.
Data extraction and risk of bias assessment Data extraction was done using a tailored data extraction template that was created using guidelines outlined in the Cochrane Handbook for Systematic Reviews of Interventions. 26 Relevant data including the author, year of publication, type of publication and journal published in, study location, study design, sample size and baseline characteristics, intervention features, outcome measurements and key findings were extracted into an Excel sheet template.
The quality of the studies that met all the inclusion criteria was assessed using the Cochrane collaboration risk of bias tool. 27 Specifically, the risk of bias in generation of the randomisation sequence, allocation concealment and blinding (participants, personnel and outcome assessors), incomplete outcome data and selective reporting were assessed as high, low or unclear. Two authors (GM and KM) assessed the risk of bias and disagreements were resolved by consensus.

Synthesis of the results
Qualitative synthesis of all the studies that met the inclusion criteria described above was done by summarising the characteristics and findings of the individual studies.
The study characteristics and findings were summarised in form of a table. We used text to describe different strategies used in the recruitment, training of CHW and in the implementation of interventions for control of hypertension. We characterised the CHW intervention by examining the recruitment process for CHW-whether drawn from government employees or not and the duration of training offered in readiness for the implementation of the interventions. We also categorised the CHW interventions depending on the content and place where interventions were offered. The content of the CHW interventions was focused on either behavioural communication for lifestyle change or the role of CHW as a mediator between patient and healthcare system. The interventions were either home/community based or clinic based. We also categorised studies based on whether they had reported significant reduction in BP or improvement in the number of participants with controlled BP. The patterns for different CHW interventions and outcomes across different studies was described in the narrative.

Patient and public involvement
We did not involve patients or members of the public in the design, or conduct, or reporting, or dissemination plans of this research.

RESULTS
The search strategy identified 1557 records through database searching (n=1525) and reference lists (n=32). After excluding duplicates, a total of 1383 records were reviewed(figure 1). Out of these, 1346 were excluded because information provided in the title and abstract did not meet the inclusion criteria leaving 36 potentially Open access eligible studies for full text review. Of these, 22 did not meet all the inclusion criteria and were excluded for reasons(some more than one), that included not being interventional studies, [28][29][30][31][32][33] not based in LMICs, [34][35][36][37][38][39][40][41][42][43] being protocols of studies, 44 45 wrong study population [46][47][48] and not reporting on BP as an outcome. 28 35 49 Thus, a final 14 studies were used for final data extraction, twelve being cluster randomised trials 22 50-60 and the other two being interventional pretest and posttest studies. 61 62 The summary characteristics of the included papers is included in table 1. The study populations were hypertensive patients in six studies, 22 53 55-57 60 had at least one CVD risk factor in two studies 52 59 and in six studies the participants involved the general population. 50 51 54 58 61 62 All the studies involved adult populations except one study that involved children and young people aged 3-39 years. 54 The duration of the interventions ranged from 3 months to 2 years. Geographically, nine studies were from South Asia, 52-54 56-61 three from sub-Saharan Africa 50 51 55 and one from East Asia 62 and one from South America. 22

Risk of bias for the included studies
The risk of bias of the included studies is shown in figure 2. The risk of selection bias as result of sequence generation and allocation concealment was low in 12 (86%) of the studies and high in 2 (14%). The risk of performance bias and reporting bias due to lack of blinding of participants, personnel and outcome assessors was low in eight (57%) and high in one, but unclear in five (36%) of the studies. The risk of attrition bias (lost to follow-up) was low in 11 (79%), high in one and unclear in two studies while risk of bias due to selective outcome reporting was low in 11 (79%) of the studies and unclear in 3 (21%).

Recruitment and training of CHW
Given the nature of CHW intervention for management of hypertension, the CHW acted as both provider and recipients of the intervention. We, therefore, examined the recruitment and training requirements for CHW applied in different studies. While all the studies met the inclusion criteria of CHW defined as a lay health worker with basic training to supply community members access to health and social services, the recruitment and training of the same was different across the studies. In all of the studies CHW were persons with at least 8-10 years of education drawn from the local community but in some of the studies 58 61 the CHW were specifically female. Most of the studies 55-57 59 used government CHW already working in the healthcare system while other studies 51-54 58 60 recruited CHW specifically for the study following same criterion used in recruiting the Government CHWs. There was no standard training for the CHW across the different studies in this review. The CHW underwent various forms of training to be able to carry out their roles in the studies. The training period ranged from 2 days to 6 weeks with ongoing support from the healthcare workers. In some of the studies the trainings were shorter ranging from 2 to 5 days 22 56 58 59 while others ranged from 4 to 6 weeks. 52-54 60 61 In some of the studies the training period was staggered throughout the study period. 52 57 61 In one of the studies the length of the training period for CHW was not specified. 55 Similarly, the content of the training was different across the studies. The content of training included, home health education on CVD risks and behaviour change communication strategies, 55 57 58 60 basics of hypertension and assessments of CVD risk factors to include measurements technique for BP monitoring and anthropometric measurements, 22 52 53 56 58 59 61 as well as referral procedure for hypertensive patients 58 and survey methods. 53 The recruitment and the CHW training details was not reported in 2 of the studies. 50 51 Content and approaches of the CHWs interventions The CHWs intervention were designed to promote BP control mainly for hypertensive patients and those with CVD risks but also targeted prevention of high BP in healthy individuals. The interventions were either home based or community based with an exception of one study, 51 which incorporated the use of CHWs in the primary health clinic to assist nurses in the management of hypertension.
The content of the activities implemented by the CHWs during the interventions was similar across many of the studies. In addition to the screening or monitoring of hypertension through BP measurements and audits which was the main outcome measure in this review, the CHW were also involved in other activities geared to the management and control of hypertension. First, the major activity in the CHW interventions as outlined in table 1 was health promotion through home-based health education and lifestyle counselling 22 52-55 57 58 60 and community level behaviour change communication. 50 56 61 62 Health education included teaching about hypertension, motivation to engage in care and support for healthy lifestyle change such as reduction in salt intake. Second, in one of the studies 59 CHW were involved in CVD risk assessment using a mobile tablet-based CVD risk assessment tool. Third, in addition to the health education and BP monitoring, one trial incorporated physical activity component of 60 min of heart exercise three times a week for a period of 3 months. 62 Fourth, the CHWs provided follow-up for hypertensive patients and supported patients by monitoring treatment adherence in one of the trials. 53 Finally, in some studies CHWs were used as mediators between patients and the healthcare system by providing referral and encouraging linkage to care for those requiring hypertensive treatment. 55 59 61 Outcomes and main findings of the studies The outcomes for the CHWs interventions were different for various studies as shown in table 1. The reported primary outcome in most of the studies 22 50 52-55 57 58 was changes in mean systolic BP (SBP) while other studies 51 56 59 61 reported proportion of participants with controlled BP (SBP <140 mm Hg and diastolic BP (DBP) <90 mm Hg) Open access as a primary outcome. There was significant reduction in the mean SBP in seven studies 22 50 52 54 57 58 60 while in two of the studies 53 55 the reduction in mean SBP was insignificant. Two of the RCTs reported a reduction in the usual rise in BP with age among children and young adults 54 and normotensive adults in the general population. 58 Similarly, three studies 56 57 61 reported significant improvement in the proportion of participants with controlled BP as result of the CHW interventions while three other studies 51 55 59 did not find any significant improvement in the BP control for participants. It is notable that even for studies which reported negative results in the control of BP, there were positive effect on linkage to care, 55 59 treatment adherence 51 53 and inter-heart risk score. 53 In other studies there was improvement in the primary outcome of mean change in Framingham risk score, 62 and reduction in the proportion of patients with moderate or high CVD risk level. 51 Other outcomes reported in the studies were changes in DBP, 55-57 60 changes in urinary sodium, 50 proportion of the population with undiagnosed hypertension, proportions who had their BP measured and those retained in care among the diagnosed hypertensive patients, 51 as well as difference in the proportion of patients on hypertension treatment. 51 59 In one RCT that had participants with at least one CVD risk factor, FBS among diabetes patients and mean number of daily cigarettes among smokers were reported as primary outcomes in addition to change in SBP. 52 In this study, CHWs interventions had a positive effect on SBP but had inconclusive effect on FBS and mean number of cigarettes smoked. 52 Outcomes trends in relation to the implementation strategy of the CHW intervention Studies whose CHW intervention focused on community-based/home-based behavioural change Author  Open access communication 22 50 52 54 57 58 60 had significant reduction in SBP and significant improvement in the proportion of participants with controlled BP. 56 57 61 On the other hand, interventions that focused on the role of CHW as mediators between patient and healthcare system through referral, linkage to care and monitoring drug adherence 51 53 55 59 did not have significant impact on BP control.
Although the studies lacked a standard requirement for CHW training in terms of duration and content, training was an important component of the CHW intervention for management and control of hypertension. Studies that had training ranging from 4 to 6 weeks had positive outcomes with those that staggered the trainings across the entire intervention period all showing positive outcomes 52 57 61 in the control and management of high BP.

DISCUSSION
Weak healthcare systems and a rising burden of CVD calls for health system innovations in the management of CVD in LMICs. CHWs have been suggested as a way to achieve that goal, with their potential ability to quickly integrate into the healthcare system. With short training periods, CHW can provide community-based care that is cost-effective and achieve high-quality outcomes. 7 Our review examined the nature and the role CHWs can play in management of hypertension in LMIC. This review found that, in general, studies that linked CHWs with existing public healthcare infrastructure enhanced control and management of BP over and above usual care. The CHW interventions had positive effects in the reduction of BP, linkage to care, treatment adherence and in reducing CVD risk level among both hypertensive and normotensive individuals in LMICs. This underscores the important role CHWs would play in the management of hypertension yet at a cheaper cost in countries with leaner economic muscle. [63][64][65] The review further showed that CHW play diverse roles ranging from preventive, therapeutic and health systems utilisation in management of hypertension.
With the growing burden of NCDs, primary prevention is a major pillars in the control of these diseases in LMICs. 66 In light of critical shortages in the health workforce in LMICs, CHWs provide cheaper alternative that would form the backbone of most primary healthcare (PHC) services for management and control of both communicable and NCDs. 67 The studies in this review demonstrate that task-shifting of roles such as health education, interpersonal communication on lifestyle modifications with a focus on primary prevention, screening for early diagnosis and supporting selfmanagement behaviour can lead to significant reduction of BP. Studies from developing countries show that CHWs have high acceptability at local community level which, may contribute to the dual benefit of providing both cheaper and acceptable labour in addition to the direct contribution in BP control. 68 While trained CHW may not perform in the same capacity as trained nurses and health educators, with appropriate and specifically focused training and supervision they can successfully contribute to the management of hypertension, as demonstrated by many of the studies reviewed. In the current review, we did not find any standards in the training of CHW for management of hypertension. The training duration ranged from 2 days to 6 weeks and the content was different across the studies depending on the focus of the intervention. The reviews showed that CHWs intervention entailed screening, promotion and monitoring of BP and its control strategies at both home and community levels where only basic PHC approaches were required. The basics required here could be easy and faster to teach with no need for unnecessary scientific details and the favourable study results from the current review show that such training as the CHWs received is enough to yield demonstrable behaviour change and BP modulation outcomes. 22 50-62 There is general agreement in the reviewed literature that CHWs can contribute to significant reduction of BP and hypertension as a key modifiable risk factor for CVD and premature death, 1 2 especially in the LMICs. 3 This review shows that enjoining CHWs in the screening and care of hypertensive patients from such countries has positive results in care of such patients. Most of the studies in this review had low risk of selection bias in both sequence generation and allocation concealment through randomisation (11 studies), had low performance bias because they had both participants and investigators blinded (8 studies), had blinding of assessors and so detection bias was minimal (9 studies), and had selective reporting bias minimised at conceptualisation and implementation of the protocol as opposed to allowing a direct influence of the outcomes at dissemination stage (11 studies) strengthens the evidence of our review. As such, the evidence deduced on importance of CHWs in mitigation of hypertension becomes especially critical for countries with less resources, an ageing population, an increase in sedentary lifestyles and other lifestyle risk factors, and a concomitant direct increase in proportions of the general population who are hypertensive. 2 The literature suggests a way out of the increasing incidence of hypertension in these countries and rising proportion of persons with poorly controlled BP. The CHWs drawn from these communities would advance the care needed and supplement the lean professional workforce available. CHWs have cultural understanding which is crucial in providing the necessary linkage between community and healthcare system. 13 The current review also demonstrates that their roles can be diverse yet effective in the control and management of high BP and other cardiovascular risk factors.

Study limitations and strengths
Our study represents a scope review of approaches and outcomes specific to CHW interventions in the management and control of hypertension in LMICs. The strengths of the current study are that we conducted comprehensive searches of databases to ensure that all relevant publications were identified. We also reduced potential Open access bias in the review by having the authors independently screen through the search results and extract the data autonomously. However, the study is limited in that, due to diversity of the study participants, interventions and outcomes of the studies included in the review, a quantitative synthesis (meta-analysis)of the overall effect of CHW interventions was not possible and therefore outcomes were summarised for individual studies.
Implications of the results for practice, policy and future research This study showed that CHWs drawn from community are an important resource in the management and control of hypertension. Preference should be given to CHW interventions focused on behaviour change communication and lifestyle counselling for reduction of high BP for both hypertensive and normotensive individuals. There is a need for adoption of standard curricula for training of CHW for the control and management of hypertension to guide translation of such interventions in different settings in LMICs. Future reviews should look into the overall effect of the various components of CHW interventions and their costeffectiveness in the management and control of CVDs.

CONCLUSIONS
In conclusion, the review suggests that CHWs interventions linked with support and/or supervision from healthcare workers provides a promising avenue for achieving improvements in hypertension control in LMICs. There is need to adopt this and integrate CHW community-based lifestyle interventions in PHC for overall reduction of CVD risks.
Contributors GWM conceived the study idea. GWM and KM performed the literature search. GWM and KM performed data extraction and evidence synthesis. GWM wrote the first draft of the manuscript. JP and KM critically revised the manuscript. GWM, KM and JP approved the final version of the manuscript. GWM acted as the guarantor and is responsible for the overall content of the manuscript.
Funding This research was supported by the Consortium for Advanced Research Training in Africa (CARTA).

Competing interests None declared.
Patient consent for publication Not applicable.
Ethics approval This paper involved a synthesis of publicly available articles and therefore did not require ethical approval.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data sharing not applicable as no datasets generated and/or analysed for this study. This research involved a synthesis of publicly available articles and did not generate datasets.
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