Review papers : Statistical models for estimating prevalence and incidence of parasitic diseases

Vlas, Sake J. de; Nagelkerke, N. J. D.; Habbema, J. Dik F.; Oortmarssen, GJ van

doi:10.1177/096228029300200102

Cited by 19 publications

(10 citation statements)

References 28 publications

(15 reference statements)

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“…14,19 In situations in which we found a scattering around the line with a slope of 2 after plotting the variation against the mean of repeated S. japonicum egg counts (Figure 2), similar plots for S. mansoni show that all individual cases are located below such a line. 14 Perhaps this difference in variability is caused by the differences in the location of both worms since S. japonicum worms normally live in lower parts of the intestinal system, so that eggs deposited in clumps are therefore less prone to mixing.…”

Section: Discussionmentioning

confidence: 53%

“…Such a distribution for variation in repeated daily egg counts is a common assumption for other helminthic infections, such as hookworm and S. mansoni. 13,14,19 The observed day-to-day variation is a combination of within-stool variation (both concentration of eggs at particular locations in the feces and/ or microclustering of eggs) and a certain day-to-day component. This day-to-day component probably is a common phenomenon for other helminths living in or next to the intestine.…”

Section: Discussionmentioning

confidence: 99%

“…A slope of b near 2.0 indicates that the negative binomial distribution could be an adequate representation of such data. 13,14 Deming regression was used instead of ordinary linear regression because measurement variation has to be considered in both the dependent (log variance) and the independent variable (log mean). 15 We chose to minimize the perpendicular distance of each point to the regression line, so that equal weight was given to measurement error of the xvalue and the y-value.…”

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confidence: 99%

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Variations in fecal Schistosoma japonicum egg counts.

Yu¹,

Vlas²,

Yuan³

et al. 1998

The American Journal of Tropical Medicine and Hygiene

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Abstract. Variations in fecal Schistosoma japonicum egg counts were studied in ZhuXi administrative village, JiangXi Province, China. Population stool examinations were collected with duplicate, standard, 41.5-mg Kato-Katz thick smears on seven consecutive days for 570 individuals from two natural (individual) villages: village I with high endemicity and village II with low endemicity. The proportion of individuals with at least one positive count increased from 42.4% after a single measurement to 68.3% after seven measurements in village I (n ϭ 356), and from 17.0% to 36.0% in village II (n ϭ 214), respectively. This demonstrates a very high variation in repeated S. japonicum egg counts and a considerable lack of sensitivity of the Kato-Katz technique; light and moderate infections are especially missed with a single or a few measurements. The observed day-to-day variation in individual egg counts is highly aggregated (variance higher than the mean) and suggestive of a negative binomial distribution. For five individuals on three days, repeated sampling from different locations of a stool specimen shows a clear trend with egg counts decreasing from the beginning of the stool to the end and from the outside layer to the center. Ten multiple samples from a particular subsection (10-30 g) of a stool specimen for 44 positive individuals still showed aggregation in egg counts, particularly for high intensities of infection. This means that the aggregation in repeated daily S. japonicum egg counts cannot be explained alone by a specific day-to-day component and variation in the concentration of eggs at different locations in the stool. There also exists clustering of eggs within parts of the stool.Most control programs and epidemiologic studies on Schistosoma japonicum and S. mansoni infection are based on the detection of parasite eggs using the modified KatoKatz method. 1-4 Generally, levels of egg excretion are used as an index of the intensity of infection. Individual diagnosis of infection is commonly based on one stool examination. However, for S. mansoni it has been shown that a single stool examination considerably underestimates the prevalence; many light infections are especially missed. 5 Fecal egg counts as a quantitative measure of infection on S. mansoni in epidemiologic studies are the result of inter-and intraindividual variations: the former reflecting egg counts varying from individual to individual caused by differences in worm loads, and the latter reflecting egg count fluctuation for an individual with a given worm load from time to time and/or within a fecal specimen. [5][6][7][8][9] Based on a stochastic model that takes into account this inter-and intra-individual variation in egg counts, projections can be made of how many individuals are truly infected with S. mansoni in a population. 10 We expect similar mechanisms to exist for S. japonicum infection, but thus far detailed studies have not been undertaken. 11 Imperfect diagnosis of S. japonicum by routine stool examination has however been ...

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Section: Discussionmentioning

confidence: 53%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Variations in fecal Schistosoma japonicum egg counts.

Yu¹,

Vlas²,

Yuan³

et al. 1998

The American Journal of Tropical Medicine and Hygiene

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“…Another study showed a higher FPR of both IHA and ELISA (IHA 32.7∼44.2%; ELISA 61.6%; Zhou et al 2007). Results of our meta- (1) The sensitivity of an examination method varies with the prevalence and intensity in a community (Devlas et al 1993); (2) different geographical characteristics like lake region and mountainous region ; (3) different diagnostic agents of schistosomiasis (Xu et al 2005); (4) size of the sample. To assess the value of any a diagnostic test comprehensively, we should consider all factors that will affect the diagnostic outcome.…”

Section: Discussionmentioning

confidence: 85%

Assessing the diagnostic accuracy of immunodiagnostic techniques in the diagnosis of schistosomiasis japonica: a meta-analysis

Zhu

Xia

et al. 2010

Parasitol Res

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Immunodiagnostic tests are commonly used in the diagnosis for schistosomiasis japonica in field situation. Their diagnostic effect, however, has never been evaluated in a systematic way. We set out to review the value of tests including enzyme-linked immunosorbent assay (ELISA) and indirect hemagglutination assay (IHA) in the diagnosis of schistosomiasis japonica. A comprehensive search was conducted in order to identify all possible studies achieving the inclusion criteria. We undertook a meta-analysis of diagnostic ability that compared ELISA with IHA for the diagnosis of schistosomiasis japonica. Original articles were searched in Pubmed, Science Citation Index Expanded, Cochrane Library, Proquest and China National Knowledge Infrastructure. Data extractions were conducted independently by two reviewers. Summary receiver operating characteristic curves were used to summarize overall test performance. Funnel plot was used to analyze publication bias. Finally, 16 studies met inclusion criteria. In all studies combined, the diagnostic odds ratio (DOR) for IHA was 8.689 (95%CI 7.671 to 9.842) and ELISA was 3.691 (95%CI 3.018 to 4.515). The DOR for IHA was better than that for ELISA. IHA demonstrated TPR* = 0.721 and ELISA showed TPR* = 0.633. IHA performance was superior to that of ELISA. Nevertheless, difference of the accuracy between the two methods for diagnosis of schistosomiasis japonica has no statistical significance as shown by the result of Z test. We found that both IHA and ELISA can be used to rule in or rule out the diagnosis.

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“…This distribution is widely used in the conceptually similar field of modeling parasite burden in the population (15). If the variance of the gamma distribution for risk indices is small, the distribution of colorectal lesions at a certain age will approach a Poisson distribution.…”

Section: Epidemiology and Natural Historymentioning

confidence: 99%