Threshold-based counting techniques comparison for low ( parasites/l), intermediate ( parasites/l) and high ( parasites/l) parasitemias.

<p>Measures of variability (ME, CV, FNR) and cost-effectiveness of methods are compared for fixed threshold values : 200 HPFs for Method A, 200 WBCs for Method B, 100 parasites and 200 WBCs for Method C, and 500 WBCs or 500 parasites for Method D.</p

Statistical Properties of Parasite Density Estimators in Malaria

<div><p>Malaria is a global health problem responsible for nearly one million deaths every year around 85% of which concern children younger than five years old in Sub-Saharan Africa. In addition, around million clinical cases are declared every year. The level of infection, expressed as parasite density, is classically defined as the number of asexual parasites relative to a microliter of blood. Microscopy of Giemsa-stained thick blood films is the gold standard for parasite enumeration. Parasite density estimation methods usually involve threshold values; either the number of white blood cells counted or the number of high power fields read. However, the statistical properties of parasite density estimators generated by these methods have largely been overlooked.</p> <p> Here, we studied the statistical properties (mean error, coefficient of variation, false negative rates) of parasite density estimators of commonly used threshold-based counting techniques depending on variable threshold values. We also assessed the influence of the thresholds on the cost-effectiveness of parasite density estimation methods. In addition, we gave more insights on the behavior of measurement errors according to varying threshold values, and on what should be the optimal threshold values that minimize this variability.</p> </div

False negative rates colormap.

<p>The colormap is drawn given a two-dimensional array of FNR values. To allow for direct point-to-point numerical and visual comparison, we express the FNR as a function of the parasite density (on the -axis) and the WBC count (on the -axis) in each of the four methods. Parasite density values are generated starting with 0, at increments of 50, and ending with . Threshold values (WBCs) are generated starting with 0, at increments of 1, and ending with . Then, each pixel is assigned a value that represents the FNR-level. A color scale grading was applied to show levels. 8 degree intervals are depicted using a red-to-yellow colorspace with increasing intensity. We contour the CV at 0.001, 0.5, 10, 20, 30, 50 and 80. The gaps between each pair of neighboring contour lines is filled with a color. A logarithmic scale is used on the -axis and a linear scale is used on the -axis.</p

Coefficient of variation colormap.

<p>The colormap is drawn given a two-dimensional array of CV values. To allow for direct point-to-point numerical and visual comparison, we express the CV as a function of the parasite density (on the -axis) and the WBC count (on the -axis) in each of the four methods. Parasite density values are generated starting with 0, at increments of 50, and ending with . Threshold values (WBCs) are generated starting with 0, at increments of 1, and ending with . Then, each pixel is assigned a value that represents the CV-level. A color scale grading was applied to show levels. 7 degree intervals are depicted using a red-to-yellow colorspace with increasing intensity. We contour the CV at 10, 15, 20, 25, 30 and 50. The gaps between each pair of neighboring contour lines is filled with a color.</p

Mean error colormap.

<p>The colormap is drawn given a two-dimensional array of ME values. To allow for direct point-to-point numerical and visual comparison, we express the ME as a function of the parasite density (on the -axis) and the WBC count (on the -axis) in each of the four methods. Parasite density values are generated starting with 0, at increments of 50, and ending with . Threshold values (WBCs) are generated starting with 0, at increments of 1, and ending with . Then, each pixel is assigned a value that represents the ME-level. A color scale grading was applied to show levels. 7 degree intervals are depicted using a red-to-yellow colorspace with increasing intensity. We contour the ME at 0.5, 0.75, 1, 1.5, 3 and 10. The gaps between each pair of neighboring contour lines is filled with a color.</p

Statistical properties of PD estimators cut-offs according to methods cost for three PD levels : low ( parasites/l), intermediate ( parasites/l) and high ( parasites/l).

<p>Variability measures (ME, CV, FNR) are expressed as functions of the cost (the number of HPFs needed to stop the counting) for the four methods (A, B, C, D). This graph gives the cost for each method according to an expected amount of variability, and favours a direct comparison between methods in terms of cost. A logarithmic scale is used on the -axis for FNR.</p

Cost-effectiveness colormap.

<p>The colormap is drawn given a two-dimensional array of cost values. To allow for direct point-to-point numerical and visual comparison, we express the cost as a function of the parasite density (on the -axis) and the WBC count (on the -axis) in each of the four methods. Parasite density values are generated starting with 0, at increments of 50, and ending with . Threshold values (WBCs) are generated starting with 0, at increments of 1, and ending with . Then, each pixel is assigned a value that represents the cost-level. A color scale grading was applied to show levels. 7 degree intervals are depicted using a red-to-yellow colorspace with increasing intensity. We contour the cost at 5, 10, 15, 20, 25 and 30. The gaps between each pair of neighboring contour lines is filled with a color.</p

Cord-to-mother IgG transfer according to placental malaria.

<p>CIRC: maternal peripheral blood at delivery; CORD: cord blood, ln(CORD/CIRC): ratio representing the transfer of maternal IgG to the neonate at birth; * <0.05; ** ≤0.01; *** ≤0.001.</p

Multiplicity of infection in asymptomatic children in Senegal: relation to transmission, age and erythrocyte variants-0

Re compared as median (25th–75th percentiles) excluding zero values.<p><b>Copyright information:</b></p><p>Taken from "Multiplicity of infection in asymptomatic children in Senegal: relation to transmission, age and erythrocyte variants"</p><p>http://www.malariajournal.com/content/7/1/17</p><p>Malaria Journal 2008;7():17-17.</p><p>Published online 23 Jan 2008</p><p>PMCID:PMC2267475.</p><p></p

Multiplicity of infection in asymptomatic children in Senegal: relation to transmission, age and erythrocyte variants-1

Re compared as median (25th–75th percentiles) excluding zero values.<p><b>Copyright information:</b></p><p>Taken from "Multiplicity of infection in asymptomatic children in Senegal: relation to transmission, age and erythrocyte variants"</p><p>http://www.malariajournal.com/content/7/1/17</p><p>Malaria Journal 2008;7():17-17.</p><p>Published online 23 Jan 2008</p><p>PMCID:PMC2267475.</p><p></p