Comparing diagnostic accuracy of Kato-Katz, Koga agar plate, ether-concentration, and FLOTAC for Schistosoma mansoni and soil-transmitted helminths

Abstract

Background: Infections with schistosomes and soil-transmitted helminths exert a considerable yet underappreciated economic and public health burden on afflicted populations. Accurate diagnosis is crucial for patient management, drug efficacy evaluations, and monitoring of large-scale community-based control programs.

Methods/principal findings: The diagnostic accuracy of four copromicroscopic techniques (i.e., Kato-Katz, Koga agar plate, ether-concentration, and FLOTAC) for the detection of Schistosoma mansoni and soil-transmitted helminth eggs was compared using stool samples from 112 school children in Côte d'Ivoire. Combined results of all four methods served as a diagnostic 'gold' standard and revealed prevalences of S. mansoni, hookworm, Trichuris trichiura, Strongyloides stercoralis and Ascaris lumbricoides of 83.0%, 55.4%, 40.2%, 33.9% and 28.6%, respectively. A single FLOTAC from stool samples preserved in sodium acetate-acetic acid-formalin for 30 or 83 days showed a higher sensitivity for S. mansoni diagnosis (91.4%) than the ether-concentration method on stool samples preserved for 40 days (85.0%) or triplicate Kato-Katz using fresh stool samples (77.4%). Moreover, a single FLOTAC detected hookworm, A. lumbricoides and T. trichiura infections with a higher sensitivity than any of the other methods used, but resulted in lower egg counts. The Koga agar plate method was the most accurate diagnostic assay for S. stercoralis.

Conclusion/significance: We have shown that the FLOTAC method holds promise for the diagnosis of S. mansoni. Moreover, our study confirms that FLOTAC is a sensitive technique for detection of common soil-transmitted helminths. For the diagnosis of S. stercoralis, the Koga agar plate method remains the method of choice.

Figure 1. Diagnostic methods used to detect S. mansoni and soil-transmitted helminth infections.

The flowchart details the diagnostic approaches and their temporal sequence, as well as the amount of stool examined for the detection of helminth eggs and larvae, and the comparison of the different diagnostic tools applied to 112 stool samples from school children in Azaguié-IRFA, Côte d'Ivoire, in June 2008.

Figure 2. Prevalence of S. mansoni and soil-transmitted helminth infections.

Bar charts indicate the prevalence of S. mansoni (A) and soil-transmitted helminth infections, i.e., hookworm (B), T. trichiura (C), and A. lumbricoides (D) among 112 school children from Azaguié-IRFA, Côte d'Ivoire, in June 2008. Results are stratified by diagnostic methods. The combined results from the different methods were considered as diagnostic ‘gold’ standard. Fresh stool examinations were subjected to triplicate Kato-Katz thick smears, a single Koga agar plate test, and a single FLOTAC examination. The fresh stool sample for FLOTAC (0 days) was homogenized in SAF. The SAF-preserved stool samples were examined once with the ether-concentration method (after 40 days) and 3 times with the FLOTAC method (at days 10, 30, and 83 post-stool collection). Prevalence estimates for S. mansoni using the FLOTAC method only considered the results of FS7. With regard to soil-transmitted helminth infections, the combined results of FS4 and FS7 were considered.

Figure 3. Geometric mean (GM) fecal egg counts according to different diagnostic techniques.

Bar charts indicate the GM of fecal egg counts (as expressed in eggs per gram of stool (EPG) according to different techniques for the diagnosis of S. mansoni (A), hookworm (B), A. lumbricoides (C), and T. trichiura (D) in stool samples from 112 school children from Azaguié-IRFA, Côte d'Ivoire, in June 2008. The results for the FLOTAC method are presented separately for FS4 and FS7. Error bars indicate 95% confidence intervals (CIs) of the GM.

Figure 4. S. mansoni eggs detected by the Kato-Katz or FLOTAC method.

The pictures show a S. mansoni egg as seen under a light microscope using 100× magnification. S. mansoni egg without deformation as seen in a Kato-Katz thick smear (A), and egg deformed through the influence of zinc sulphate in FS7 and centrifugation as seen under the FLOTAC reading disc (B).