Low sensitivity of malaria rapid diagnostic tests stored at room temperature in the Brazilian Amazon Region

Luciano T Gomes,Alvaro A.R.A Couto,Andreia F Nery,Mauro S Tada,Marinete M Povoa,Cor J.F Fontes,Vanja S.P Calvosa,Frankllin S De Santana-Filho,Maria Das Gracas C Alecrim,Tony H Katsuragawa,Giselle Mr Viana,Ana Ruth L Arcanjo

doi:10.3855/jidc.2564

Abstract

In remote areas of the Amazon Region, diagnosis of malaria by microscopy is practically impossible. This study aimed to evaluate the performance of two rapid diagnostic tests (RDTs) targeting different malaria antigens stored at room temperature in the Brazilian Amazon Region. Performance of the OptiMal Pf/Pan test and ICT-Now Pf/Pan test was analyzed retrospectively in 1,627 and 1,602 blood samples, respectively. Tests were performed over a 15-month period. Kits were stored at room temperature in five community health centres located in the Brazilian Amazon Region. RDT results were compared with thick blood smear (TBS) results to determine sensitivity, specificity, and accuracy of the RDT. The sensitivities of the OptiMal Pf/Pan test were 79.7% for Plasmodium falciparum malaria diagnosis and 85.7% for non-P. falciparum infections. The results showed a crude agreement of 88.5% for P. falciparum, and 88.3% for non-P. falciparum infections (Kappa index = 0.74 and 0.75, respectively). For the ICT-Now Pf/Pan test (CI 95%), the sensitivities were 87.9% for P. falciparum malaria diagnosis and 72.5% for non-P. falciparum infection. Crude agreement between the ICT-Now Pf/Pan test and TBS was 91.4% for P. falciparum and 79.7% for non-P. falciparum infection. The Kappa index was 0.81 and 0.59 for the final diagnosis of P. falciparum and non-P. falciparum, respectively. Higher levels of parasitaemia were associated with higher crude agreement between RDT and TBS. The sensitivities of RDTs stored at room temperature over a 15-month period and performed in field conditions were lower than those previously reported.

Highlights

In remote areas of the Amazon Region, diagnosis of malaria by microscopy is practically impossible
Similar findings were obtained by Ratsimbasoa et al, who evaluated three rapid diagnostic tests (RDTs) targeting P. falciparum pLDH and pan-malaria pLDH under storage conditions similar to those used in this study [20]
The World Health Organization (WHO) recommends that RDT should be applied in patients with parasitaemia levels above 100 parasites/ μL only when its sensitivity and specificity are above 95% [3]; the results of this study demonstrate the need for meticulous selection of the RDT to be used in programmes to control malaria, and strict adjustment of its distribution and storage routine

Summary

Introduction

In remote areas of the Amazon Region, diagnosis of malaria by microscopy is practically impossible. This study aimed to evaluate the performance of two rapid diagnostic tests (RDTs) targeting different malaria antigens stored at room temperature in the Brazilian Amazon Region. Results: The sensitivities of the OptiMal Pf/Pan test were 79.7% for Plasmodium falciparum malaria diagnosis and 85.7% for non-P. falciparum infections. Crude agreement between the ICT- Pf/Pan test and TBS was 91.4% for P. falciparum and 79.7% for non-P. falciparum infection. Conclusions: The sensitivities of RDTs stored at room temperature over a 15-month period and performed in field conditions were lower than those previously reported. Microscopic detection of Plasmodium spp. using the stained blood smears is a simple, highly sensitive and low-cost method that is the gold standard for malaria diagnosis This method is time-consuming and its interpretation requires considerable expertise, at low levels of parasitaemia. Malaria rapid diagnostic tests (RDT) are a relatively new and evolving technology which can provide parasite-based diagnosis in remote areas where microscopy is difficult to support and there is limited control of test storage conditions and supervision of users [2]

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