Field Evaluation of a High Throughput Loop Mediated Isothermal Amplification Test for the Detection of Asymptomatic Plasmodium Infections in Zanzibar.

Abstract

BACKGROUND:New field applicable diagnostic tools are needed for highly sensitive detection of residual malaria infections in pre-elimination settings. Field performance of a high throughput DNA extraction system for loop mediated isothermal amplification (HTP-LAMP) was therefore evaluated for detecting malaria parasites among asymptomatic individuals in Zanzibar. METHODS:HTP-LAMP performance was evaluated against real-time PCR on 3008 paired blood samples collected on filter papers in a community-based survey in 2015. RESULTS:The PCR and HTP-LAMP determined malaria prevalences were 1.6% (95%CI 1.3-2.4) and 0.7% (95%CI 0.4-1.1), respectively. The sensitivity of HTP-LAMP compared to PCR was 40.8% (CI95% 27.0-55.8) and the specificity was 99.9% (CI95% 99.8-100). For the PCR positive samples, there was no statistically significant difference between the geometric mean parasite densities among the HTP-LAMP positive (2.5 p/μL, range 0.2-770) and HTP-LAMP negative (1.4 p/μL, range 0.1-7) samples (p = 0.088). Two lab technicians analysed up to 282 samples per day and the HTP-LAMP method was experienced as user friendly. CONCLUSIONS:Although field applicable, this high throughput format of LAMP as used here was not sensitive enough to be recommended for detection of asymptomatic low-density infections in areas like Zanzibar, approaching malaria elimination.