The protocol for the systematic review is registered in the International Prospective Register for Systematic Reviews (PROSPERO) [167175]. The protocol has been designed and reported based on the guidelines Preferred Reporting Items for Systematic Reviews and Meta-analyses Protocols (PRISMA-P) checklist (28). (Figure. 1).
Exclusion and inclusion criteria:
All observational studies (cross-sectional, case-control or follow-up studies) published between 1 January, 2000 to 31 December, 2019 which reported a prevalence or incidence along with risk factors of hypertension in adults textile workers in LMICs will be included. Original articles, conference proceedings or abstracts reporting the outcome of interest will also eligible for inclusion.
Articles will be excluded if the adult workers are from other than cotton textile industry. Non-English articles will not be included as the authors are not proficient in other languages. Moreover, commentaries, editorials, symposium proceedings, and systematic reviews will also be excluded.
The inclusion and exclusion criterion is shown in Table 1.
Information sources and search strategy
We will carry out the systematic literature search on the major electronic databases including PubMed, CINAHL Plus, Science Direct, and Cochrane because they are usually considered as good databases for systematic reviews. Furthermore, gray literature (non-published, non-reviewed papers internal, or online repositories) will also be searched. In addition, the bibliography of the included records will be assessed to identify relevant studies. Besides, cross-referencing of identified systematic review will also be performed to include pertinent studies. Two researchers will independently search the data bases (NA, AF).
The search term will be group into following categories of interest: population (textile, workers, factory workers, and mill workers), exposure (risk-factors, factors, predictors, prevalence, prevalence and factors) outcome (hypertension, blood pressure, systolic blood pressure, diastolic blood pressure, hypertension, high blood pressure and HTN), and settings (LMICs). Additionally, indexed keywords in the Medical Subject Headings (MeSH) will be used in order to ensure uniform search terms. The search strategy will be piloted to ensure sufficient specificity and sensitivity. The preliminary search strategy is illustrated in Table 2. We will limit the search findings to human studies conducted in the adult workers.
Study selection
Citation management system (Endnote software) will be used to manage the search results from the different databases(29). Firstly, the titles will be screened based on eligibility criteria using Endnote software. Secondly, the abstract will be screened within the short-listed studies guided by the inclusion and exclusion criteria. Lastly, the full text of potentially analyzed studies will be retrieved. For the reliability of selected studies among the two reviewers, a pre-defined screening tool will be prepared and pilot testing will be done as per the inclusion criteria. Two reviewer will depict outcome measures subsequently after reviewing the studies to confirm the relevance of the included articles. All studies will be given as a unique study ID to identify the data for this review. Each reviewer will give strong justification for excluding studies. Any discrepancies between the both reviewers will be resolved by mutual consensus. If it still persists, the third reviewer will be referred to conclude the final decision about including the study. The Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) flow diagram will be used to report the study selection process as given in figure 1.
Data collection process
Data will be extracted onto a customized sheet in Excel that will be pilot tested prior to initiating the data extraction process. This sheet will be completed by two independent reviewers (NA, AF) for the eligible studies. Data extraction tables filled by two reviewers will be compared to confirm that all main findings are included. During the data extraction process a third assessor will be involved if any discordant data is witnessed. The primary data extraction table is shown in Table 3. Besides, existing studies on this research domain have been revised to assess items in the extraction form. The form included the study’s title, primary author, year of publication, study setting, country of study, objective, study design, study population, reviewer name, BP measurement method, prevalence of hypertension, risk-factors of hypertension co-morbidities, study limitations, included/excluded, reason for exclusion, and quality appraisal of included studies.
Evaluation of study quality
The quality of the included studies will be evaluated by standardized quality assessment tool which will be conducted by two authors (NA, AF). Mixed Methods Appraisal Tool (MMAT) tool will be used to evaluate the methodological quality of all non-randomized studies(30). This tool is used to assess several aspects like selection of study participant, study tool, exposure period, missing data, measurement in outcomes, and selection of the reported result. Two reviewer (NA, AF) will rate each study as critical, serious, moderate, or low risk of bias via judgment of the gathered information. If there are limited information then the risk of bias will be categorized as “no information” or the reviewer will contact corresponding study authors for complete information.
Synthesis of included studies
The findings of the studies will be synthesized narratively. Firstly, we will conduct a descriptive analysis of all the selected studies to note down their main characteristics that includes study title, study authors, publication year, study aim, study methods, sampling strategy, characteristics of study participants and study outcomes. After that narrative synthesis will be conducted in which included studies will be grouped under outcomes. Both reviewers (NA, AF) will read each included study several times to extract data and group-related results. Finally, the reviewers will highlight potential risk factors that are associated with blood pressure among textile workers. For the quantitative studies, we will conduct a sub-group analysis under different categories including gender and textile department. Measures of association i.e. relative risks, odds ratio and prevalence ratios will be reported. Furthermore, we will also provide a narrative of confounders or effect modifiers being adjusted in different quantitative studies.