Malaria rapid diagnostic devices: performance characteristics of the ParaSight F device determined in a multisite field study

Abstract

Microscopic detection of parasites has been the reference standard for malaria diagnosis for decades. However, difficulty in maintaining required technical skills and infrastructure has spurred the development of several nonmicroscopic malaria rapid diagnostic devices based on the detection of malaria parasite antigen in whole blood. The ParaSight F test is one such device. It detects the presence of Plasmodium falciparum-specific histidine-rich protein 2 by using an antigen-capture immunochromatographic strip format. The present study was conducted at outpatient malaria clinics in Iquitos, Peru, and Maesod, Thailand. Duplicate, blinded, expert microscopy was employed as the reference standard for evaluating device performance. Of 2,988 eligible patients, microscopy showed that 547 (18%) had P. falciparum, 658 (22%) had P. vivax, 2 (0.07%) had P. malariae, and 1,750 (59%) were negative for Plasmodium. Mixed infections (P. falciparum and P. vivax) were identified in 31 patients (1%). The overall sensitivity of ParaSight F for P. falciparum was 95%. When stratified by magnitude of parasitemia (no. of asexual parasites per microliter of whole blood), sensitivities were 83% (>0 to 500 parasites/microl), 87% (501 to 1,000/microl), 98% (1,001 to 5,000/microl), and 98% (>5,000/microl). Device specificity was 86%.

FIG. 1

Box plots of asexual parasite density and test line intensity (excluding mixed infections). (A) Positive assay results from P. falciparum-positive specimens showed an increase in test line intensity with increased parasitemia (n = 547). (B) Test line intensity of positive assays from non-P. falciparum Plasmodium-positive specimens was not associated with predictable changes in parasitemia (n = 97). The bold horizontal lines indicate the median parasitemia for each intensity group, and the white boxes show the 25th and 75th percentiles. The whisker caps extending from each box indicate the 10th and 90th percentiles, with significant outliers shown as individual points.