Comparative evaluation of four techniques for the diagnosis of Plasmodium falciparum infections.
ABSTRACT Four diagnostic techniques for Plasmodium falciparum infection were evaluated against serial parasite dilutions and on identical field samples. These were (i) Giemsa-stained thick blood films (GTF), (ii) acridine orange-stained thick (AOTF) and thin (AOTnF) blood films, (iii) the quantitative buffy coat technique (QBC); and (iv) the ParaSight-F dipstick test (PS). PS had a consistently higher sensitivity and speed, was easiest to learn, and required no laboratory facility. The 100% sensitivity cut-off points against known parasite densities (per mm3) were: PS, 30; GTF, 84; QBC, 84; AOTnF, 84; AOTF, 149. In the field study, test sensitivities compared with examination of 800 microscope fields of a Giemsa-stained thin blood film were PS, 96.6%; AOTF, 93.1%; GTF, 91.4%; QBC, 89.7%; AOTnF, 82.8%. In the dilution study, one false positive result was recorded with QBC; in the field study there was one false positive each with PS, AOTnF and AOTF. When a newly trained microscopist examined samples of the parasite dilutions, the 100% sensitivity cut-off points were AOTF, 84; GTF, 140; QBC, 390. Total handling time was shortest with PS regardless of whether samples were processed individually or in batches of 10 or 100. The ParaSight-F test is recommended as the diagnostic tool for the future.
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ABSTRACT: BACKGOUND: Treatment of confirmed malaria patients with Artemisinin-based Combination Therapy (ACT) at remote areas is the goal of many anti-malaria programs. Introduction of effective and affordable malaria Rapid Diagnosis Test (RDT) in remote areas could be an alternative tool for malaria case management. This study aimed to assess performance of the OptiMAL dipstick for rapid malaria diagnosis in children under five. Malaria symptomatic and asymptomatic children were recruited in a passive manner in two community clinics (CCs). Malaria diagnosis by microscopy and RDT were performed. Performance of the tests was determined. RDT showed similar ability (61.2%) to accurately diagnose malaria as microscopy (61.1%). OptiMAL showed a high level of sensitivity and specificity, compared with microscopy, during both transmission seasons (high & low), with a sensitivity of 92.9% vs. 74.9% and a specificity of 77.2% vs. 87.5%. By improving the performance of the test through accurate and continuous quality control of the device in the field, OptiMAL could be suitable for use at CCs for the management and control of malaria.Parasites & Vectors 05/2012; 5:103. · 3.25 Impact Factor
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ABSTRACT: In many epidemiological studies time to event data are grouped into strata (or clusters), such as, geographic region, districts, villages and so on. Consequently, cluster specific effects on survival times may cause an extra variation. Under such circumstance, it is substantive importance to draw inference on the nature and magnitude of these effects albeit the primary focus being on survival times. In model based analysis the aforesaid effect (called frailty) are usually accommodated by the use of frailty survival models. The goal of this thesis is to model the time to first malaria infection due to p. falcuiprum in children’s living near to the Gilgel Gibe dam using Cox proportional hazards and shared gamma frailty models with an attempt to compare these two modelling approaches. We apply the two modelling approaches to the analysis of malaria dataset. The dataset comprise time to first malaria infection of 2040 under 10 children observed during the period from July 2008 to June 2010. This study revealed that, Cox PH model estimates the risk of malaria infection for children residing in proximity to the dam is significantly lower than children’s living in distant from the dam. However, when we take the clustering of children within locality into account (using frailty model) there was no statistical significant difference in hazard of contracting malaria between the two groups, namely at risk and control. The likelihood ratio test of the heterogeneity parameter (theta) in all the fitted frailty models, however, showed that theta is significantly different from zero (P<0.000), indicating that there is a clear clustering of study subjects (children) with in their localities. In the future, it is better to see also the result by including a frailty term at least in a pairwise manner and also spatial distance of households, in the modelling of time-to-malaria.06/2012; Lambert academic publishing., ISBN: 978-3-659-19711-6
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ABSTRACT: Recent developments in diagnostic techniques for malaria, particularly DNA probes and sero-immunology, have raised questions as to how these techniques might be used to facilitate malaria diagnosis at the most peripheral levels of the primary health care system. At present, malaria diagnosis is based on the standard microscopic examination of blood films in most field epidemiologic studies and is likely to remain so in the immediate future in Africa. The objective of this study was to assess inter-observer agreement for the examination of Giemsa-stained slides for Plasmodium falciparum parasites. Children aged 0 to 10 years were enrolled yearly in Bancoumana village (West Africa), mainly during the transmission season (June to October). The blood smears obtained from the persistently negative children in June 1996, August 1996, October 1996 and March 1997 were systematically re-examined. A stratified random sample (10%) proportional to the following parasite density classes 1--100, 101--5000, and 5001 and over was taken from the slides collected. The kappa statistics and the intra-class correlation were used as measures of agreement the first and the second slide examinations. The weighted kappa statistic, widely used as a chance-corrected measure for nominal agreement, showed excellent inter-observer agreement (kappaw=0.7926; 95% CI [0.7588, 0.8263]; p=0.01). The intra-class correlation co-efficient had the same value of 0.7926 confirming the appropriateness of the weighted kappa statistic. Inter-observer agreement for slides read as negative by one observer, or as containing more than 100 parasites per mul, was excellent: 97% (493/506) and 92% (145/158), respectively. In contrast, the inter-observer agreement for slides read by one observer as containing 1--100 parasites/mul was poor, 36% (96/268). In field conditions in Mali, there was a high reproducibility for slides reported as negative or as having more than 100 parasites per mul. However, smears with readings of 1--100 parasites per mul were less reproducible and should be re-examined carefully.Malaria Journal 09/2013; 12(1):335. · 3.40 Impact Factor