Patient and public involvement statement
Patients were not involved in the development of this protocol.
Study design
This systematic review protocol was developed and reported (see checklist) following the guidelines in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P) statement It has also been registered within the International Prospective Register of Systematic Reviews (PROSPERO) database (CRD42020175165).
Information sources:
The review will be conducted based on the items outlined in the PRISMA statement [13] . The following databases were systematically searched for eligible studies in English: PubMed Central (1800 to March 2020), ovid-Embase (1974 -March 2020), ovid-MEDLINE (1946-March 2020), ovid-PsycINFO (1806 to March 2020) and web of science (1900-March 2020). Automated database searches covered the period from when the earliest electronic records were available (e.g., 1900 in the case of Web of Science) until March 2020. Electronic searches will be additionally complimented by a manual search of reference lists of eligible articles.
Search strategy
The search terms used included keywords and variants of “schistosomiasis”, “prevalence” and “intensity”. We used Boolean operators “AND” to combine the categories and “OR” to join the terms within each category. The search string used was: Schistosomiasis OR “Schistosoma Mansoni” OR “Schistosoma Haematobium” OR “Urinary Schistosomiasis” OR “Intestinal Schistosomiasis” AND Prevalence OR Burden AND “Infection intensity” OR “intensity of infection”.
Eligibility criteria
A detailed description on population, intervention, comparison, and outcome of the systematic review is outlined in Textbox 1. We will include studies on human schistosomiasis (infection caused by either S. mansoni or S. haematobium) that document prevalence and/or intensity data distributed by sex. These studies could be observational or intervention studies using cross-sectional or longitudinal designs with no age or geographical restrictions. Studies not written in English, animal studies, quantitative studies not measuring the outcome of interest, studies on human schistosomiasis caused by other schistosoma species will be excluded. Also unpublished manuscripts, conference proceedings, reviews, editorials, commentaries, letters to editors and author replies will be excluded.
Population: Human population (no age or geographical restriction) diagnosed with schistosomiasis (Schistosoma mansoni or Schistosoma haematobium).
Intervention/exposure: Human sex is the exposure of interest for this study which we define as male and female as reported by authors in the search articles.
Comparison: The primary comparison will be schistosomiasis prevalence and/or infection intensity between male and female participants.
Outcome: The primary outcome measures are the male to female ratios of prevalence and/or intensity of infection.
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Textbox 1:Population, intervention, comparison, and outcome (PICO) of systematic review
Screening and selection procedure
All citations obtained using the search strategy will be imported into Endnote (Endnote X9, Thomson Reuters, San Francisco, CA), and duplicates will be deleted. The remaining unique records will be imported into Microsoft Excel where screening for relevance and eligibility will take place. Three (DA, JC and JT) reviewers will screen the titles, abstracts, figures and tables independently and in duplicates. Any disputes will be resolved by team consensus.
Data extraction
Relevant data will be extracted by three reviewers from eligible publications into a predefined extraction Microsoft Excel sheet developed for this review. Data that will be extracted include:
- Publication details: title, journal, author(s), year of publication, country and year in which study was carried out
- Study design: type of study (cross-sectional, longitudinal, cohort, case-control), sampling method, type of drug administration strategy and platform, mass drug administration era, type of Schistosoma species, diagnostic method and treatment uptake rate (coverage)
- Study population demographics: number of individuals in study, population characteristics including age and demographic information
- Data for outcome measures: male: female ratios of prevalence and intensity of infection at baseline and follow up. Also, if available socio-cultural and economic determinants identified
For cross-sectional studies, we will extract study population demographics and outcome measures of each study area separately if available. For longitudinal studies, we will extract this information at baseline and the first follow up. Data extraction will be done independently, and a small random proportion will be done in duplicates by three reviewers (DA, JC and JT).
Data synthesis
A descriptive synthesis of the results will be undertaken in line with the outcomes of this study. Summary tables of characteristics of the included studies and the male: female prevalence/intensity ratios will be presented. Forest plots will be used to visually assess the extent of heterogeneity between studies. A narrative synthesis will provide a summary of the prevalence and intensity of schistosomiasis according to age, as well as the identified risk factors. Limitations of the studies will be discussed in detail. Implications of the review as well as areas for future research will also be provided.
Where possible, we will also perform subgroup analysis by age group, geographical region and mass drug administration era, in order to assess differences between the strength of association by geography and potential impact of contextual confounders which may vary by geography. This will also be extended to a subgroup analysis across the two Schistosoma species if there are enough studies.
Risk of bias assessment for eligible studies
In this review, the methodological quality of studies will not be assessed. This will allow more studies to be included in the review. We will however stratify our results to account for possible selection bias in sampling and include this in the discussion section. The main criteria for inclusion are whether the studies contain data on prevalence and intensity of infection distributed by sex.
Ethics statement
Our review will not require an ethics committee approval or written informed consent because it relies entirely on published data.