Performance evaluation of Baermann techniques: The quest for developing a microscopy reference standard for the diagnosis of Strongyloides stercoralis
PLoS neglected tropical diseases, vol. 15, pp. e0009076
Abstract
BACKGROUND: Soil-transmitted helminths (STH) are common in low and middle income countries where there is lack of access to clean water and sanitation. Effective diagnosis and treatment are essential for the control of STH infections. However, among STH parasites, Strongyloides stercoralis is the most neglected species, both in diagnostics and control strategies. Diagnostic methods cover different approaches, each with different sensitivities and specificities, such as serology, molecular techniques and microscopy based techniques. Of the later, the Baermann technique is the most commonly used procedure. In the literature, several ways have been described to perform the Baermann method, which illustrates the overall lack of a '(gold) reference standard' method for the diagnosis of S. stercoralis infection. In this study we have evaluated the performance of three Baermann techniques in order to improve the reference standard for the microscopic diagnosis of S. stercoralis infection thereby facilitating individual case detection, mapping of the disease and proper evaluation of treatment responses. METHODS/PRINCIPAL FINDINGS: A community based cross sectional study was conducted at Zenzelima, Bahir Dar Zuria Ethiopia. A total of 437 stool samples were collected and analyzed by the following procedures: conventional Baermann (CB), modified Baermann (MB), and modified Baermann with charcoal pre-incubation (MBCI). The diagnostic sensitivity and Negative Predictive Value (NPV) of each technique was calculated using the combination of all the three techniques as a composite reference standard. Our result indicated that larvae of S. stercoralis were detected in 151 (34.6%) stool samples. The prevalence of S. stercoralis infection based on the three diagnostic methods was 9.6%, 8.0%, and 31.3% by CB, MB, and MBCI respectively. The sensitivity and NPV for CB, MB, and MBCI were 26.7% and 70.8%, 22.1% and 69.6%, and 87.0% and 93.2%, respectively. The MBCI showed significant difference (P- value = <0.001) in the sensitivity and NPV values when compared with CB and MB values. The agreement between CB, MB, and MBCI with the composite reference standard was 31.8%, 26.7%, 89.6%, respectively. CONCLUSION/SIGNIFICANCE: Our results suggest the superior performance of MBCI. It is relatively easy to implement, simple to perform and comparatively cheaper. The CB is by far the commonly used method in routine diagnostic although this technique significantly underestimates the true burden of the disease and thereby contributing to the exclusion of S. stercoralis from the control strategies. Therefore, MBCI is recommended as a routine microscopy-based diagnostic test for S. stercoralis infection, particularly in settings where molecular procedures are not available.
Authors 11
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Woyneshet Gelaye corresponding
Affiliation as printed
Bahir Dar University, College of Medicine and Health Science, Bahir Dar, Ethiopia
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Hospital Clínic de Barcelona · Barcelona Institute for Global Health · Universitat de Barcelona
Affiliation as printed
Barcelona Institute for Global Health (ISGlobal), Hospital Clínic-Universitat de Barcelona, Spain
Barcelona Institute for Global Health (ISGlobal), Hospital Clínic—Universitat de Barcelona, Spain
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Kenya Medical Research Institute
Affiliation as printed
Kenya Medical Research Institution, Nairobi, Kenya
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Manhiça Health Research Centre
Affiliation as printed
Centro de Investigaçao em Saúde da Manhiça (CISM), Maputo, Mozambique
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National University of Salta · Consejo Nacional de Investigaciones Científicas y Técnicas
Affiliation as printed
Universidad Nacional de Salta, Instituto de Investigaciones de Enfermedades Tropicales/CONICET, Oran, Salta, Argentina
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Hospital Clínic de Barcelona · Barcelona Institute for Global Health · Universitat de Barcelona
Affiliation as printed
Barcelona Institute for Global Health (ISGlobal), Hospital Clínic-Universitat de Barcelona, Spain
Barcelona Institute for Global Health (ISGlobal), Hospital Clínic—Universitat de Barcelona, Spain
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Affiliation as printed
Bahir Dar University, College of Science, Department of Biology, Bahir Dar, Ethiopia
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Affiliation as printed
Bahir Dar University, College of Science, Department of Biology, Bahir Dar, Ethiopia
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National University of Salta · Consejo Nacional de Investigaciones Científicas y Técnicas · Hospital Clínic de Barcelona · Barcelona Institute for Global Health · Universitat de Barcelona
Affiliation as printed
Barcelona Institute for Global Health (ISGlobal), Hospital Clínic-Universitat de Barcelona, Spain
Universidad Nacional de Salta, Instituto de Investigaciones de Enfermedades Tropicales/CONICET, Oran, Salta, Argentina
Barcelona Institute for Global Health (ISGlobal), Hospital Clínic—Universitat de Barcelona, Spain
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Leiden University · Leiden University Medical Center
Affiliation as printed
Department of Parasitology, Centre of Infectious Diseases, Leiden University Medical Centre (LUMC), Leiden, The Netherlands
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Affiliation as printed
Bahir Dar University, College of Medicine and Health Science, Bahir Dar, Ethiopia
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