Discussion

Introduction: The diagnostic performance of existing malaria RDTs is inadequate for detecting low-density infections. Although “sub-microscopic” infections are commonly asymptomatic, they contribute to the overall infectious reservoir, particularly in low-transmission areas. Detecting malaria infections during pregnancy poses a further challenge to diagnosis. During pregnancy P. falciparum can sequester in the placenta, reducing the number of circulating parasites, remaining undetected and untreated with potential adverse consequences for the pregnancy. There is an urgent need for sensitive diagnostics in these populations.

The new Alere™ Ultra-sensitive Malaria Ag P. falciparum RDT (uRDT) was developed to address the need for more sensitive, field-ready diagnostics.

Aim: To compare the performance of the uRDT with the currently used CareStart™ Malaria HRP2/pLDH VOM Combo RDT (csRDT) in asymptomatic pregnant women in a low-transmission setting in Indonesia.

Methods: As part of a larger malaria in pregnancy trial in Timika, West Papua (ISRCTN34010937), a subset of 270 stored red blood cell pellets and plasma samples were used in this study. These included 158 P. falciparum positive samples and 112 P. falciparum negative samples. Using a composite molecular reference standard comprising LAMP, qPCR and nPCR, we compared the diagnostic performance of both RDTs.

Results: The uRDT had a sensitivity of 19.6% (95% CI 13.9-26.8) and specificity of 95.5 % (89.4-98.3%), whilst these were 22.8% (16.7- 30.3%) and 98.2% (93.1- 99.7%) respectively with the conventional CareStart combo-RDT. Overall, the performance of the RDTs was not significantly different.

Conclusion: In these settings and populations of asymptomatic pregnant women, the uRDT offers no significant improvement in detecting low-density infections. Alternative diagnostic tests are urgently needed.