Performance of the OptiMAL (R) assay for detection and identification of malaria infections in asymptomatic residents of Irian Jaya, Indonesia

The OptiMAL (R) assay, a new immunochromatographic "dipstick" test for mala ria based on detection of Plasmodium lactate dehydrogenase (pLDH), is purpo rted to detect infections of similar to 200 parasites/muL of blood and to d ifferentiate between Plasmodium falciparum and non-P. falciparum. We evalua ted OptiMAL (R) performance by comparing the test strip interpretations of two independent readers with consensus results obtained independently by ex pert malaria microscopists. Unbiased measures of sensitivity were derived b y applying the OptiMAL (R) test for detection and differentiation of light, asymptomatic infections by P. falciparum and Plasmodium vivax. OptiMAL (R) readings were separated in time to determine whether the reaction signal w as stable. Microscopy identified infections in 225 of 505 individuals scree ned; those with P. falciparum (n = 170) averaged 354 asexual furms/muL and P. vivax/Plasmodium malariae (n = 112) averaged 216 asexual forms/muL of bl ood. Concordance between OptiMAL (R) and microscopy was 81%, and 78% by the two independent readings. The assay's sensitivity for detection of any mal aria species was 60.4% and 70.2% respectively and specificity was 97% and 8 9%. Most cases identified by microscopy as P. falciparum were graded as neg ative or non-falciparum by both OptiMAL (R) readers. OptiMAL (R) false nega tives as well as misidentifications were related to low parasitemias (< 500 /muL). The OptiMAL (R) assay demonstrated 88-92% sensitivity for detecting infections of 500-1,000 parasites/muL, a range covering the mean parasitemi a of primary symptomatic P. falciparum infections in malaria-naive Indonesi an transmigrants. This device was markedly less sensitive than expert micro scopy for discriminating between malaria species and is presently unsuited for use as an epidemiological screening tool. The OptiMAL (R) assay is not approved for diagnostic use but is commercially available for research purp oses only.