Analysis of malaria diagnosis discrepancies between RDTs and microscopy by nested PCR

A total of 415 samples from febrile children exhibiting either concordant (n = 108) or discordant (n = 307) results between microscopy, the gold standard diagnostic test, and two Rapid Diagnostic Tests (RDTs), OptiMAL-IT(pLDH) and AconHRP2, were analysed using polymerase chain reaction (PCR) from May to December 2011 in Gabon. The aim of the study was to analyse these discrepancies using polymerase chain reaction (PCR). Nested PCR targeting the Plasmodium ssrRNA gene was used to distinguish P. falciparum, P. malariae and P. ovale. Plasmodium falciparum was the only malaria species identified. Discrepancies frequently involved samples that were negative by microscopy and positive by AconHRP2 (90%) or Optimal-it (86%). The PCR assay detected submicroscopic infection in almost 23% of the microscopy-negative samples, whereas plasmodial DNA was not found in 77% of the AconHRP2 positivemicroscopy negative samples. Although results obtained with Optimal-it were more frequently concordant with those of PCR genotyping, the low specificity of Optimal-iT for non-falciparum malaria parasite detection resulted in a high proportion of false negative RDTs (90%) and a high frequency of tests with faint line intensity. The present study highlights the specific attributes of the different methods used to identify malaria parasite below the microscopy level of detection. RDT results that were discordant with either microscopy or PCR as the gold standard could represent a challenge for rapid, accurate fever case management in malaria endemic areas. It is necessary to pursue the development of more precise and more sensitive point-of-care diagnostic tools for malaria.