Performance of ultra-sensitive malaria rapid diagnostic test to detect Plasmodium falciparum infection in pregnant women in Kinshasa, the Democratic Republic of the Congo

Background: Low peripheral parasitaemia caused by sequestration of Plasmodium falciparum in the placenta hampers the diagnosis of malaria in pregnant women, leading to microscopy or conventional rapid diagnostic tests (RDTs) false-negative results. Although mainly asymptomatic, maternal malaria remains harmful to pregnant women and their offspring in endemic settings and must be adequately diagnosed. Ultra-sensitive RDTs (uRDTs) are thought to be more sensitive than RDTs, and their diagnostic performance was assessed in the current study in pregnant women living in Kinshasa, a stable malaria transmission area in the Democratic Republic of the Congo. Methods: To assess and compare the diagnostic performances of both RDTs and uRDTs, 497 peripheral blood samples were tested using microscopy and quantitative polymerase chain reaction (qPCR) as the index and the reference tests, respectively. The agreement between the different diagnostic tests assessed was estimated by Cohen's Kappa test. Results: The median parasite density by qPCR was 292 p/μL of blood [IQR (49.7–1137)]. Using qPCR as the reference diagnostic test, the sensitivities of microscopy, RDT and uRDT were respectively [55.7% (95% CI 47.6–63.6)], [81.7% (95%CI 74.7–87.3)] and [88% (95% CI 81.9–92.6)]. The specificities of the tests were calculated at 98.5% (95% CI 96.6–99.5), 95.2% (95% CI 92.5–97.2) and 94.4% (95% CI 91.4–96.6) for microscopy, RDT and uRDT, respectively. The agreement between qPCR and uRDT was almost perfect (Kappa = 0.82). For parasite density (qPCR) below 100 p/µL, the sensitivity of RDT was 62% (95% CI 47.1–75.3) compared to 68% (95% CI 53.3–80.4) for uRDT. Between 100 and 200 p/µL, the sensitivity of RDT was higher, but still lower compared to uRDT: 89.4% (95% CI 66.8–98.7) for RDT versus 100% (95% CI 82.3–100) for uRDT. In both cases, microscopy was lower, with 20% (95% CI 10–33.7) and 47.3% (95% CI 24.4–71.1) respectively. Conclusions: uRDT has the potential to improve malaria management in pregnant women as it has been found to be slightly more sensitive than RDT in the detection of malaria in pregnant women but the difference was not significant. Microscopy has a more limited value for the diagnosis of malaria during the pregnancy, because of its lower sensitivity.