Performance of the OptiMAL registered Assay for Detection and Identification of Malaria Infections in Asymptomatic Residents of Irian Jaya, Indonesia

The OptiMAL registered assay, a new immunochromatographic "dipstick" test for malaria based on detection of Plasmodium lactate dehydrogenase (pLDH), is purported to detect infections of similar to 200 parasites/ mu L of blood and to differentiate between Plasmodium falciparum and non-P. falciparum. We evaluated OptiMAL registered performance by comparing the test strip interpretations of two independent readers with consensus results obtained independently by expert malaria microscopists. Unbiased measures of sensitivity were derived by applying the OptiMAL registered test for detection and differentiation of light, asymptomatic infections by P. falciparum and Plasmodium vivax. OptiMAL registered readings were separated in time to determine whether the reaction signal was stable. Microscopy identified infections in 225 of 505 individuals screened; those with P. falciparum (n = 170) averaged 354 asexual forms/ registered L and P. vivax/Plasmodium malariae (n = 112) averaged 216 asexual forms/ mu L of blood. Concordance between OptiMAL registered and microscopy was 81% and 78% by the two independent readings. The assays sensitivity for detection of any malaria species was 60.4% and 70.2% respectively and specificity was 97% and 89%. Most cases identified by microscopy as P. falciparum were graded as negative or non-falciparum by both OptiMAL registered readers. OptiMAL registered false negatives as well as misidentifications were related to low parasitemias (< 500/ mu L). The OptiMAL registered assay demonstrated 88-92% sensitivity for detecting infections of 500-1,000 parasites/ mu L, a range covering the mean parasitemia of primary symptomatic P. falciparum infections in malaria-naive Indonesian transmigrants. This device was markedly less sensitive than expert microscopy for discriminating between malaria species and is presently unsuited for use as an epidemiological screening tool. The OptiMAL registered assay is not approved for diagnostic use but is commercially available for research purposes only.