Diagnostic Accuracy of Kato–Katz, FLOTAC, Baermann, and PCR Methods for the Detection of Light-Intensity Hookworm and Strongyloides stercoralis Infections in Tanzania

Abstract

Sensitive diagnostic tools are crucial for an accurate assessment of helminth infections in low-endemicity areas. We examined stool samples from Tanzanian individuals and compared the diagnostic accuracy of a real-time polymerase chain reaction (PCR) with the FLOTAC technique and the Kato–Katz method for hookworm and the Baermann method for Strongyloides stercoralis detection. Only FLOTAC had a higher sensitivity than the Kato–Katz method for hookworm diagnosis; the sensitivities of PCR and the Kato–Katz method were equal. PCR had a very low sensitivity for S. stercoralis detection. The cycle threshold values of the PCR were negatively correlated with the logarithm of hookworm egg and S. stercoralis larvae counts. The median larvae count was significantly lower in PCR false negatives than true positives. All methods failed to detect very low-intensity infections. New diagnostic approaches are needed for monitoring of progressing helminth control programs, confirmation of elimination, or surveillance of disease recrudescence.

Comparison of Nested Polymerase Chain Reaction and Real-Time Polymerase Chain Reaction with Parasitological Methods for Detection of Strongyloides stercoralis in Human Fecal Samples

“…In that study, the sensitivity and specificity of S. stercoralis real-time PCR were 88.9% and 92.7%, respectively, compared with the combination of Baermann/Koga agar as gold standard. 15 Knopp and others 13 reported that the sensitivity of the Baermann method for detection of S. stercoralis was significantly higher than that of real-time PCR (47.1% versus 17.4%; P < 0.001), while the specificity of the Baermann method was lower than that of real-time PCR (78.4% versus 93.9%).…”

“…8,22 PCR-based methods have shown variable sensitivity for detection of S. stercoralis in fecal samples. [10][11][12][13][14][15]18 For detection of intestinal nematodes in stool samples by PCR-based techniques, optimization of DNA isolation method is essential, because of existence of large amounts of PCR-inhibitory substances in fecal samples such as bacterial proteases, nucleases, cell debris, bile acids, and so forth, and also the presence of a thick and complex cuticle that covers the worms. 18,23,24 Repetto and others introduced an improved IH DNA extraction method based on efficient lysis of larvae and removal of inhibitors in the fecal samples.…”

“…5,9 Among molecular methods, real-time PCR targeting ribosomal RNA (rRNA) genes for specific detection of S. stercoralis DNA in fecal samples has been evaluated in a few studies with variable results. [10][11][12][13][14][15] Accordingly, it appears that the method of DNA extraction is a key factor influencing the results of the evaluated tests. So, to increase the sensitivity of molecular methods, utilization of an appropriate DNA extraction technique is necessary.…”

The laboratory diagnosis of Strongyloides stercoralis

“…Microscopic methodologies such as examination of Kato-Katz preparations, FLOTAC, and formalin/ethyl acetate concentrates have a low yield compared to culture 9,10 . A modified formalin/ethyl acetate method proposed by Anamnart et al improved rates of detection 9 .…”

“…The majority of Strongyloides PCR publications have used a real-time method with primers and probe published by Verweij et al 19 . This has also allowed for the development of multiplexed PCR 10,30,34,38 . Some studies evaluating the diagnostic accuracy of these PCR methods have used both morphological diagnosis and detection of PCR products as their reference standards, and are not reviewed here.…”