Sources of variability in the measurement of Ascaris lumbricoides infection intensity by Kato-Katz and qPCR

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Title: Sources of variability in the measurement of Ascaris lumbricoides infection intensity by Kato-Katz and qPCR
Author(s): Easton, AV
Oliveira, RG
Walker, M
O'Connell, EM
Njenga, SM
Mwandawiro, CS
Webster, JP
Nutman, TB
Anderson, RM
Item Type: Journal Article
Abstract: Background Understanding and quantifying the sources and implications of error in the measurement of helminth egg intensity using Kato-Katz (KK) and the newly emerging “gold standard” quantitative polymerase chain reaction (qPCR) technique is necessary for the appropriate design of epidemiological studies, including impact assessments for deworming programs. Methods Repeated measurements of Ascaris lumbricoides infection intensity were made from samples collected in western Kenya using the qPCR and KK techniques. These data were combined with data on post-treatment worm expulsions. Random effects regression models were used to quantify the variability associated with different technical and biological factors for qPCR and KK diagnosis. The relative precision of these methods was compared, as was the precision of multiple qPCR replicates. Results For both KK and qPCR, intensity measurements were largely determined by the identity of the stool donor. Stool donor explained 92.4% of variability in qPCR measurements and 54.5% of observed measurement variance for KK. An additional 39.1% of variance in KK measurements was attributable to having expelled adult A. lumbricoides worms following anthelmintic treatment. For qPCR, the remaining 7.6% of variability was explained by the efficiency of the DNA extraction (2.4%), plate-to-plate variability (0.2%) and other residual factors (5%). Differences in replicate measurements by qPCR were comparatively small. In addition to KK variability based on stool donor infection levels, the slide reader was highly statistically significant, although it only explained 1.4% of the total variation. In a comparison of qPCR and KK variance to mean ratios under ideal conditions, the coefficient of variation was on average 3.6 times larger for KK highlighting increased precision of qPCR. Conclusions Person-to-person differences explain the majority of variability in egg intensity measurements by qPCR and KK, with very little additional variability explained by the technical factors associated with the practical implementation of these techniques. qPCR provides approximately 3.6 times more precision in estimating A. lumbricoides egg intensity than KK, and could potentially be made more cost-effective by testing each sample only once without diminishing the power of a study to assess population-level intensity and prevalence.
Publication Date: 25-May-2017
Date of Acceptance: 1-May-2017
URI: http://hdl.handle.net/10044/1/49286
DOI: https://dx.doi.org/10.1186/s13071-017-2164-y
ISSN: 1756-3305
Publisher: BioMed Central
Journal / Book Title: Parasites & Vectors
Volume: 10
Copyright Statement: © The Author(s). 2017. Open Access. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Sponsor/Funder: GlaxoSmithKline Services Unlimited
Funder's Grant Number: n/a
Copyright Statement: © The Author(s). 2017. Open Access. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Keywords: Science & Technology
Life Sciences & Biomedicine
Parasitology
Kato-Katz
qPCR
Ascaris lumbricoides
Diagnostics
Deworming
Impact evaluation
Soil-transmitted helminths
Measurement error
SOIL-TRANSMITTED HELMINTHS
FECAL EGG COUNTS
REAL-TIME PCR
SCHISTOSOMA-MANSONI
DRUG EFFICACY
GASTROINTESTINAL PARASITES
INTESTINAL PARASITES
DIAGNOSTIC-ACCURACY
TRICHURIS-TRICHIURA
ETHER-CONCENTRATION
Ascaris lumbricoides
Deworming
Diagnostics
Impact evaluation
Kato-Katz
Measurement error
Soil-transmitted helminths
qPCR
Science & Technology
Life Sciences & Biomedicine
Parasitology
Kato-Katz
qPCR
Ascaris lumbricoides
Diagnostics
Deworming
Impact evaluation
Soil-transmitted helminths
Measurement error
SOIL-TRANSMITTED HELMINTHS
FECAL EGG COUNTS
REAL-TIME PCR
SCHISTOSOMA-MANSONI
DRUG EFFICACY
GASTROINTESTINAL PARASITES
INTESTINAL PARASITES
DIAGNOSTIC-ACCURACY
TRICHURIS-TRICHIURA
ETHER-CONCENTRATION
1108 Medical Microbiology
1117 Public Health And Health Services
Mycology & Parasitology
Tropical Medicine
Publication Status: Published
Article Number: ARTN 256
Appears in Collections:Faculty of Medicine
Epidemiology, Public Health and Primary Care



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