Evaluation of a non-isotopic polymerase chain reaction-based assay to detect and predict treatment failure of Plasmodium vivax malaria in travellers

With the emergence of chloroquine-resistant Plasmodium vivax (CRPV), new tests to detect P. vivax and predict response to therapy would be useful for clinical and research applications. We performed a 'blinded' evaluation of a non-isotopic (colourimetric) polymerase chain reaction (PCR) based assay (Digene SHARP Signal(TM) System) compared with microscopy and PCR/radiometric probe hydrization of ribosomal ribonucleic acid genes (RPH) for the detection of P. vivax malaria in 182 febrile travellers. Compared with PCR/RPH as the reference standard, the colourimetric assay had a sensitivity of 100% and specificity of 98%. Using microscopy as the reference standard, 84 of 87 patients with P. vivax infection had a positive colourimetric assay. The 3 patients with a negative assay were subsequently shown to be infected with P. ovale as determined by PCR/RPH. In a subset of patients followed longitudinally, the colourimetric assay was positive in 5 of 13 patients 6 or more days after initiation of therapy. Of these 5 patients, 4 were subsequently demonstrated to be infected with CRPV as determined by treatment failure in vivo and/or chloroquine blood levels. A positive assay result 6 or more days after initiation of therapy was associated with subsequent treatment failure (P<0.01). This non-isotopic assay is a sensitive, specific, and rapid method for the detection of P. vivax PCR products and may prove useful in predicting treatment failure.