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Parasitological versus molecular diagnosis of strongyloidiasis in serial stool samples: how many?

Published online by Cambridge University Press:  23 January 2017

E. Dacal
Affiliation:
Department of Parasitology, National Centre for Microbiology, Instituto de Salud Carlos III, Majadahonda, Madrid 28220, Spain
J.M. Saugar
Affiliation:
Department of Parasitology, National Centre for Microbiology, Instituto de Salud Carlos III, Majadahonda, Madrid 28220, Spain
T. Soler
Affiliation:
Department of Parasitology, National Centre for Microbiology, Instituto de Salud Carlos III, Majadahonda, Madrid 28220, Spain
J.M. Azcárate
Affiliation:
Department of Parasitology, National Centre for Microbiology, Instituto de Salud Carlos III, Majadahonda, Madrid 28220, Spain
M.S. Jiménez
Affiliation:
Department of Parasitology, National Centre for Microbiology, Instituto de Salud Carlos III, Majadahonda, Madrid 28220, Spain
F.J. Merino
Affiliation:
Department of Microbiology and Parasitology, Hospital Universitario Severo Ochoa, Leganés, Madrid 28911, Spain
E. Rodríguez*
Affiliation:
Department of Parasitology, National Centre for Microbiology, Instituto de Salud Carlos III, Majadahonda, Madrid 28220, Spain
*

Abstract

Strongyloidiasis is usually an asymptomatic disease in immunocompetent patients, caused by Strongyloides stercoralis. However, in immunocompromised patients it can produce a severe clinical profile. Therefore, a correct diagnosis is necessary in these cases and in those chronic asymptomatic patients. The low sensitivity of classical parasitological techniques requires the analysis of multiple serial stool samples. Molecular diagnostic techniques represent an improvement in the detection of the parasite. The objective of this study was to evaluate the minimum number of samples necessary to achieve maximum sensitivity by real-time polymerase chain reaction (PCR). A total of 116 stool samples from 39 patients were analysed by direct microscopic observation, agar culture, Harada–Mori and real-time PCR, in one, two, three and four or more consecutive samples. After two serial samples, 6 out of 39 patients were positive by parasitological and molecular techniques, while 16 of them were real-time PCR positive, and all the patients detected by parasitology were also detected by the molecular technique, reaching 100.00% sensitivity versus 83.00% when analysing a single sample. These data also reflect apparently low specificity (51.52%) and positive predictive value (PPV) (27.27 %) values, due to the high number of cases detected by real-time PCR and not by parasitological techniques. These cases were confirmed as true positives when analysing three, four or more samples from the same patient. In conclusion, the application of molecular techniques decreases the number of serial stool samples necessary to give a diagnosis with the maximum sensitivity.

Type
Research Papers
Copyright
Copyright © Cambridge University Press 2017 

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