Research Article: Low Sensitivity of the Formol-Ethyl Acetate Sedimentation Concentration Technique in Low-Intensity Schistosoma japonicum Infections

Date Published: February 24, 2009

Publisher: Public Library of Science

Author(s): Tore Lier, Gunnar S. Simonsen, Tianping Wang, Dabing Lu, Hanne H. Haukland, Birgitte J. Vennervald, Maria V. Johansen, Juerg Utzinger

Abstract: BackgroundThe endemic countries are in a diagnostic dilemma concerning Schistosoma japonicum with increasing difficulties in diagnosing the infected individuals. The formol-ethyl acetate sedimentation concentration technique is preferred by many clinical microbiology laboratories for the detection of parasites in stool samples. It is potentially more sensitive than the diagnostic methods traditionally used.Methodology/Principal FindingsWe evaluated the technique for detection of low-intensity S. japonicum infections in 106 stool samples from China and used a commercial kit, Parasep Midi Faecal Parasite Concentrator. One stool sample and one serum sample were collected from each person. As reference standard we used persons positive by indirect hemagglutination in serum and positive by Kato-Katz thick smear microscopy (three slides from a single stool), and/or the hatching test. We found the sedimentation technique to have a sensitivity of only 28.6% and specificity of 97.4%.Conclusion/SignificanceThis study indicates that the sedimentation technique has little to offer in the diagnosis of low-intensity S. japonicum infections, at least when only a single stool sample is examined.

Partial Text: Schistosomiasis japonica is still a major public health problem, especially in China, despite great achievements during the past 50 years in controlling this parasitic disease. Diagnosis is a key for decision-making, both on individual and community levels. The current epidemiologic situation in the Schistosoma japonicum-endemic countries (China, the Philippines and Indonesia) has made the use of many common diagnostic assays problematic [1]. Low-intensity infections reduce the sensitivity of tests which demonstrate eggs in stool such as the Kato-Katz thick smear [2] and the hatching test [3], especially when only a single stool sample is available for examination. Antibody detection tests suffer from low specificity, often due to persistent antibodies from previously treated infections [4]–[6].

A total of 144 samples were selected from a larger collection (1360 samples) based on the result of Kato-Katz thick smear and hatching test (approximately one-third positive). However, 38 samples were discarded because of inadequate sample size or missing results thus leaving 106 samples for further analysis. This study population of 106 persons consisted of 56% males and 44% females aged 7–76 years (mean 39 years). The number of positive persons for each test was 47 (44%) for IHA, 19 (18%) for Kato-Katz thick smear, 27 (26%) for hatching test and 10 (9%) for the sedimentation test. A person was considered positive by the “reference standard” if IHA was positive together with Kato-Katz positive and/or hatching test positive. A total of 28 persons (26%) were reference standard positive, including 15 who were hatching positive/Kato-Katz negative and 5 who were Kato-Katz positive/hatching negative. Eight persons were positive in both tests. Results from Kato-Katz thick smear, the only fully quantitative test in this study, showed that the majority of the samples had low egg count, and hence probably were low-intensity infections. In the reference standard positive group there were 7 samples containing <40 egg per gram of stool (EPG), 5 containing 40–99 EPG and 1 sample containing 368 EPG. In this study we found that the sedimentation technique, when a commercial kit (Parasep Midi Faecal Parasite Concentrator) and a single stool sample was used, had a disappointingly low sensitivity in diagnosing low-intensity S. japonicum infections. However, the number of samples tested is low and further studies are needed to confirm the results. Source: http://doi.org/10.1371/journal.pntd.0000386

 

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