Improving the Specificity of Plasmodium falciparum Malaria Diagnosis in High- Transmission Settings with a Two-Step Rapid Diagnostic Test and Microscopy Algorithm
Date
2017Author
Murungi, Moses
Fulton, Travis
Reyes, Raquel
Matte, Michael
Ntaro, Moses
Mulogo, Edgar Mugema
Nyehangane, Dan
Juliano, Jonathan J.
Siedner, Mark J.
Boum II, Yap
Ross M, Boycee
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Poor specificity may negatively impact rapid diagnostic test (RDT)-based diagnostic strategies for malaria. We performed real-time PCR on a subset of subjects who had undergone diagnostic testing with a multiple-antigen (histidine-rich protein 2 and pan-lactate dehydrogenase pLDH [HRP2/pLDH]) RDT and microscopy.
We determined the sensitivity and specificity of the RDT in comparison to results of PCR for the detection of Plasmodium falciparum malaria. We developed and evaluated a two-step algorithm utilizing the multiple-antigen RDT to screen patients, followed by confirmatory microscopy for those individuals with HRP2-positive (HRP2_)/ pLDH-negative (pLDH_) results. In total, dried blood spots (DBS) were collected from 276 individuals. There were 124 (44.9%) individuals with an HRP2_/pLDH_ result, 94 (34.1%) with an HRP2_/pLDH_ result, and 58 (21%) with a negative RDT result. The sensitivity and specificity of the RDT compared to results with real-time PCR were 99.4% (95% confidence interval [CI], 95.9 to 100.0%) and 46.7% (95% CI, 37.7 to 55.9%), respectively. Of the 94 HRP2_/pLDH_ results, only 32 (34.0%) and 35 (37.2%)
were positive by microscopy and PCR, respectively. The sensitivity and specificity of the two-step algorithm compared to results with real-time PCR were 95.5% (95% CI, 90.5 to 98.0%) and 91.0% (95% CI, 84.1 to 95.2), respectively. HRP2 antigen bands demonstrated poor specificity for the diagnosis of malaria compared to that of real time PCR in a high-transmission setting.
The most likely explanation for this finding is the persistence of HRP2 antigenemia following treatment of an acute infection. The two-step diagnostic algorithm utilizing microscopy as a confirmatory test for indeterminate HRP2_/pLDH_ results showed significantly improved specificity with little loss of sensitivity in a high-transmission setting.
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