The accuracy of the Kato-Katz technique in identifying individuals with soil-transmitted
helminth (STH) infections is limited by day-to-day variation in helminth egg excretion,
confusion with other parasites and the laboratory technicians' experience. We aimed
to estimate the sensitivity and specificity of the Kato-Katz technique to detect infection
with Ascaris lumbricoides, hookworm and Trichuris trichiura using a Bayesian approach
in the absence of a 'gold standard'. Data were obtained from a longitudinal study
conducted between January 2004 and December 2005 in Samar Province, the Philippines.
Each participant provided between one and three stool samples over consecutive days.
Stool samples were examined using the Kato-Katz technique and reported as positive
or negative for STHs. In the presence of measurement error, the true status of each
individual is considered as latent data. Using a Bayesian method, we calculated marginal
posterior densities of sensitivity and specificity parameters from the product of
the likelihood function of observed and latent data. A uniform prior distribution
was used (beta distribution: alpha=1, beta=1). A total of 5624 individuals provided
at least one stool sample. One, two and three stool samples were provided by 1582,
1893 and 2149 individuals, respectively. All STHs showed variation in test results
from day to day. Sensitivity estimates of the Kato-Katz technique for one stool sample
were 96.9% (95% Bayesian Credible Interval [BCI]: 96.1%, 97.6%), 65.2% (60.0%, 69.8%)
and 91.4% (90.5%, 92.3%), for A. lumbricoides, hookworm and T. trichiura, respectively.
Specificity estimates for one stool sample were 96.1% (95.5%, 96.7%), 93.8% (92.4%,
95.4%) and 94.4% (93.2%, 95.5%), for A. lumbricoides, hookworm and T. trichiura, respectively.
Our results show that the Kato-Katz technique can perform with reasonable accuracy
with one day's stool collection for A. lumbricoides and T. trichiura. Low sensitivity
of the Kato-Katz for detection of hookworm infection may be related to rapid degeneration
of delicate hookworm eggs with time.
(c) 2009 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights
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