To assess the accuracy of molecular biology techniques for the diagnosis of S. stercoralis infection.
We will search the following databases: PubMed (MEDLINE), EMBASE, SCOPUS, CINAHL, and LILACS. Other resources:
- conference proceedings of the American Society of Tropical Medicine & Hygiene (ASTMH) meeting, of the International Congress of Parasitology (ICOPA), and of the European Conference of Tropical Medicine and International Health (ECTMIH), held in the last two years.
- we will also check the reference lists of all included studies for other potentially relevant research and review authors’ personal collections.
We will attempt to identify all relevant studies regardless of language or publication status (published, unpublished, in press, and ongoing).
Types of study to be included
We will include all diagnostic accuracy studies evaluating a molecular biology technique in comparison to serology and/or other fecal-based methods for the diagnosis of S. stercoralis infection. In case data from cohort studies are sufficient for the purpose of the review, case-control studies will not be considered for inclusion. Otherwise, case-control studies will be included. We will exclude non-human animal studies and duplicate publications. For studies that pool multiple intestinal parasites into one outcome measure (for example, multiplex PCR including other soil-transmitted helminths) we will try to disaggregate the data or we will contact study authors to request disaggregated data. We will not include the study in case of impossibility to retrieve disaggregated data.
Condition or domain being studied
Strongyloides stercoralis is a soil-transmitted helminth (STH) affecting around 370 million people worldwide, particularly in remote rural areas. Like the other STH, S. stercoralis larvae, which live in the soil, infect humans by penetration of skin (mostly feet). In the human organism, the parthenogenetic adult female worm settles in the intestine and releases eggs, which hatch into larvae in the bowel. Some larvae are excreted with feces, but others can penetrate the last part of the bowel or perianal skin and re-start migration and maturation inside the human body: the infection becomes chronic through this auto-infective cycle. Chronic strongyloidiasis is characterized by unspecific, mostly mild symptoms involving the gastrointestinal tract (abdominal pain, diarrhea), the respiratory system (symptoms resembling asthma, chronic obstructive pulmonary disease), the skin (pruritus, rash). However, in immunosuppressed individuals the infection can become severe, with complications due to a heavier load of parasites, including intestinal obstruction, paralitic ileus, respiratory failure, death. First-line treatment is with ivermectin, which demonstrated to be well tolerated and highly effective, although the optimal dosage (stat dose of 200 mcg/kg or multiple doses) is debated. However, treatment of the severe syndrome is more complicated as failures tend to occur with the standard regimens. There are reports on the use of parenteral, veterinary formulations of ivermectin for the treatment of severely-ill patients, but currently the evidence is not robust enough to support this kind of intervention.
It is obviously advisable to diagnose and treat strongyloidiasis when still in the chronic, indolent phase.
The gold standard for the diagnosis of strongyloidiasis is still lacking. The diagnostic tools for S. stercoralis infection should be characterized by high sensitivity, considering that strongyloidiasis is a potentially-fatal infection, with a highly tolerable short-term treatment. However, most available tests have insufficient sensitivity, while there are concerns about the specificity of serology, that at the moment demonstrates the best sensitivity. Molecular methods have been implemented in this context, with the aim to achieve the highest sensitivity, preserving a high specificity. However, different studies report either better or worse accuracy of molecular methods compared to other fecal-based methods. Some variables (such as setting in which the research was conducted, population, type of molecular technique, comparator) might influence the global evaluation of the accuracy of these novel techniques. In conclusion, the accuracy of molecular biology techniques for the diagnosis of S. stercoralis infection should be better defined, possibly clarifying their role in different settings (diagnosis in the field and in non-endemic, industrialized areas).
We will include studies in patients with presumptive exposure to S. stercoralis infection, conducted in endemic as well as in non-endemic areas. We will include studies with and without a control (healthy individuals) group. Studies conducted on immunosuppressed patients will be considered for inclusion.
Results of molecular biology techniques (“standard” PCR, real-time PCR, multiplex PCR, LAMP) for the diagnosis of S. stercoralis infection. We will include methods performed on stool as well as methods performed on other biological materials.
- composite reference standard based on a combination of tests
- latent class analysis.
Accuracy of molecular methods for the diagnosis of S. stercoralis infection.
Data extraction, (selection and coding)
Dora Buonfrate (DB) and Ana Requena (AR) will independently review the titles and abstracts yielded by the search, and will identify all studies that potentially meet the inclusion criteria for this review. After we obtain the full text articles of screened records that may meet the inclusion criteria, we will independently assess whether or not each study meets the inclusion criteria using an eligibility form. When DB and AR do not initially reach a consensus, Andrea Angheben (AA) will make the final inclusion decision. We will document all excluded studies with their reason for exclusion.
Data extraction and management
Two review authors, DB and AR, will independently perform data extraction using a pre-designed data extraction form. We will resolve any disagreements regarding the data extraction by discussion between the two authors. When necessary, a third review author, AA, will facilitate discussion until consensus is reached. We will enter the extracted data into Review Manager (RevMan) (RevMan 5.3).
We will collect data about the study design, study population (including number of individuals, whether patients or healthy individuals) and setting (including rural and urban status), inclusion and exclusion criteria, details about the reference standard (tests/methods and performance) and the index test (technical details of molecular technique, including genetic target and probe sequence, performance), and statistical methods.
Risk of bias (quality) assessment
Two review authors, DB and AR, will independently assess the methodological quality of each included trial using the QUADAS- 2 tool, as recommended in STARD (Standards for Reporting of Diagnositc Accuracy). QUADAS-2 consists of four key domains: patient selection, index test, reference standard, flow and timing. Each is assessed in terms of risk of bias and the first three in terms of concerns regarding applicability. Signalling questions are included to assist in judgements about risk of bias. Risk of bias is judged as “low”, “high”, or “unclear”. We will consider low the risk of bias for a certain domain if the signaling question for that domain indicates a low risk of bias. If the answer to at least one signaling question is “no”, the risk of bias for that domain will be considered high. We will rate a criterion as "unclear" if we cannot acquire sufficient details or if the impact of specific methodological characteristics is unclear. When necessary, a third review author, Zeno Bisoffi (ZB) will facilitate discussion until consensus is reached. We will record all assessments in 'Risk of bias' tables and produce 'Risk of bias' summary graphs.
Strategy for data synthesis
The values of sensitivity and specificity will be automatically computed in RevMan 2014. We will present individual study results graphically by plotting the estimates of sensitivity and specificity (and their 95% confidence intervals (CIs) in both forest plots and receiver operating characteristics (ROC) space. We will assess the operating point sensitivity and specificity of the diagnostic tests under scrutiny by a bivariate random-effects approach. The procedure permits generation of a hierarchical summary receiver operating characteristic (HSROC) model. The results of the bivariate model will be used to calculate likelihood ratios, and summary diagnostic odds ratio (DOR). Bivariate analysis will be performed on STATA 11 software.
Analysis of subgroups or subsets
Subgroup analyses will be performed in relation to:
- Different method (as described in the intervention paragraph)
- Different comparator
- Different study setting (endemic vs non-endemic area)
- Different population (immunocompetent vs immunosuppressed patients)
If there are 10 or more included studies available for an intervention, we will systematically investigate heterogeneity through subgroup analysis or meta-regression, or both.
Publication of the results of the review in a peer-reviewed journal
Contact details for further information
Via Sempreboni 5
Organisational affiliation of the review
Dr Dora Buonfrate, Sacro Cuore Don Calabria Hospital Dr Ana Requena-Mendez, Barcelona Institute for Global Health Dr Andrea Angheben, Sacro Cuore Don Calabria Hospital Ms Andrea Fittipaldo, Mario Negri Institute Dr Michela Cinquini, Mario Negri Institute Dr Mario Cruciani, ULSS20 Verona Dr Zeno Bisoffi, Sacro Cuore Don Calabria Hospital
Formal screening of search results against eligibility criteria
Risk of bias (quality) assessment
PROSPERO This information has been provided by the named contact for this review. CRD has accepted this information in good faith and registered the review in PROSPERO. CRD bears no responsibility or liability for the content of this registration record, any associated files or external websites.