Evaluation of Urine CCA Assays for Detection of Schistosoma mansoni Infection in Western Kenya

Hillary L Shane,W Evan Secor,Susan P Montgomery,Bernard Abudho,Sara E Butler,Jennifer R Verani,Anna J Blackstock,Pauline N M Mwinzi,Diana M S Karanja,Jeffrey Michael Bethony

doi:10.1371/journal.pntd.0000951

Abstract

Although accurate assessment of the prevalence of Schistosoma mansoni is important for the design and evaluation of control programs, the most widely used tools for diagnosis are limited by suboptimal sensitivity, slow turn-around-time, or inability to distinguish current from former infections. Recently, two tests that detect circulating cathodic antigen (CCA) in urine of patients with schistosomiasis became commercially available. As part of a larger study on schistosomiasis prevalence in young children, we evaluated the performance and diagnostic accuracy of these tests—the carbon test strip designed for use in the laboratory and the cassette format test intended for field use. In comparison to 6 Kato-Katz exams, the carbon and cassette CCA tests had sensitivities of 88.4% and 94.2% and specificities of 70.9% and 59.4%, respectively. However, because of the known limitations of the Kato-Katz assay, we also utilized latent class analysis (LCA) incorporating the CCA, Kato-Katz, and schistosome-specific antibody results to determine their sensitivities and specificities. The laboratory-based CCA test had a sensitivity of 91.7% and a specificity of 89.4% by LCA while the cassette test had a sensitivity of 96.3% and a specificity of 74.7%. The intensity of the reaction in both urine CCA tests reflected stool egg burden and their performance was not affected by the presence of soil transmitted helminth infections. Our results suggest that urine-based assays for CCA may be valuable in screening for S. mansoni infections.

Highlights

There has been increased interest in the development and assessment of control and elimination programs for schistosomiasis [1]
Control efforts for schistosomiasis have in part been hampered by the lack of a sensitive and accurate test that can be utilized to rapidly map the prevalence of the disease in different areas
We found that the new tests performed very well to detect schistosomiasis in children in western Kenya, an area with a high prevalence of Schistosoma mansoni infections

Summary

Introduction

There has been increased interest in the development and assessment of control and elimination programs for schistosomiasis [1]. The method most commonly used for diagnosis of Schistosoma mansoni infection is the detection of eggs in stool by the Kato-Katz method. Benefits of the Kato-Katz method are very high specificity, low cost, and relatively simple technologic requirements. The Kato-Katz method is time consuming and exposes laboratory workers to potentially harmful fresh stools which can contain infectious agents. In order to overcome some of the pitfalls of the Kato-Katz method, there has been interest in developing new, more sensitive tests for the diagnosis of schistosomiasis. These tests often employ immunologic methods based on the detection of antibodies or antigens in blood or urine

Methods

Results

Discussion

Conclusion