Field Evaluation of a Real-Time Fluorescence Loop-Mediated Isothermal Amplification Assay, RealAmp, for the Diagnosis of Malaria in Thailand and India

Abstract

Background.  To eliminate malaria, surveillance for submicroscopic infections is needed. Molecular methods can detect submicroscopic infections but have not hitherto been amenable to implementation in surveillance programs. A portable loop-mediated isothermal amplification assay called RealAmp was assessed in 2 areas of low malaria transmission.

Methods.  RealAmp was evaluated in 141 patients from health clinics in India (passive surveillance) and in 127 asymptomatic persons in Thailand (active surveillance). The diagnostic validity, precision, and predictive value of RealAmp were determined using polymerase chain reaction (PCR) as the reference method. A pilot study of RealAmp was also performed on samples from patients presenting at a Thai health center.

Results.  A total of 96 and 7 positive cases were detected in India and Thailand, respectively, via PCR. In comparison with nested PCR, the sensitivity and specificity of RealAmp in India were 94.8% (95% confidence interval [CI], 88.3%–98.3%) and 100% (95% CI, 92.1%–100%), respectively, with correct identification of all 5 Plasmodium vivax cases. In Thailand, compared with pooled real-time PCR, RealAmp demonstrated 100% sensitivity (95% CI, 59.0%–100%) and 96.7% specificity (95% CI, 91.7%–99.1%). Testing at the health center demonstrated RealAmp's potential to serve as a point-of-care test with results available in 30–75 minutes.

Conclusion.  RealAmp was comparable to PCR in detecting malaria parasites and shows promise as a tool to detect submicroscopic infections in malaria control and elimination programs worldwide.