Direct Estimation of Sensitivity of Plasmodium falciparum Rapid Diagnostic Test for Active Case Detection in a High-Transmission Community Setting

Abstract

Community-based active case detection of malaria parasites with conventional rapid diagnostic tests (cRDTs) is a strategy used most commonly in low-transmission settings. We estimated the sensitivity of this approach in a hightransmission setting in Western Kenya. We tested 3,547 members of 912 households identified in 2013-2014 by index children with (case) and without (control) cRDT-positive malaria. All were tested for Plasmodium falciparum with both a cRDT targeting histidine-rich protein 2 and with an ultrasensitive real-time polymerase chain reaction (PCR). We computed cRDT sensitivity against PCR as the referent, compared prevalence between participant types, and estimated cRDT detectability as a function of PCR-estimated parasite density. Parasite prevalence was 22.9% by cRDTs and 61.5% by PCR. Compared with children aged < 5 years or adults aged > 15 years, geometric mean parasite densities (95% CI) were highest in schoolage children aged 5-15 years (8.4 p/uL; 6.6-10.6). The overall sensitivity of cRDT was 36%; among asymptomatic household members, cRDT sensitivity was 25.5% and lowest in adults aged > 15 years (15.8%). When modeled as a function of parasite density, relative to school-age children, the probability of cRDT positivity was reduced in both children aged < 5 years (odds ratio [OR] 0.48; 95% CI: 0.34-0.69) and in adults aged > 15 years (OR: 0.35; 95% CI: 0.27-0.47). An HRP2-detecting cRDT had poor sensitivity for active P. falciparum case detection in asymptomatic community members, and sensitivity was lowest in highly prevalent low-density infections and in adults. Future studies can model the incremental effects of high-sensitivity rapid diagnostic tests and the impacts on transmission.

The prevalence and density of asymptomatic Plasmodium falciparum infections among children and adults in three communities of western Kenya

“…We confirmed that transmission intensity remained low in Kap-Kip [17,31], where asymptomatic P. falciparum parasitemia was rarely detected by varATS qPCR (0.22% prevalence), and established that high malaria transmission occurs in Ajigo, where 42% of individuals had asymptomatic parasitemia. Webuye demonstrated moderate transmission with 10% prevalence of asymptomatic parasitemia, which is lower than what has been previously described at this site [32,33], possibly reflecting micro-heterogeneity or seasonal differences, as our study was performed during months when rainfall is historically lower in western Kenya.…”

Genotyping cognate Plasmodium falciparum in humans and mosquitoes to estimate onward transmission of asymptomatic infections

“…gDNA was extracted from mosquito abdomens and DBS samples using a Chelex-100 protocol 65 . gDNA from each DBS and mosquito was tested in duplicate using a duplex TaqMan real-time PCR (quantitative PCR (qPCR)) assay targeting the P. falciparum pfr364 motif and the human β-tubulin gene 66 . Samples were defined as P. falciparum positive if: (i) both replicates amplified P. falciparum and both Ct values were <40 or (ii) 1 replicate amplified P. falciparum and Ct value was <38.…”

Impact of asymptomatic Plasmodium falciparum infection on the risk of subsequent symptomatic malaria in a longitudinal cohort in Kenya

“…Previous studies that detected asymptomatic infections using microscopy also reported an increased short-term hazard of symptomatic illness among children within 9 to 30 days after having an asymptomatic malaria infection ( Le Port et al, 2008 ; Njama-Meya et al, 2004 ). We built upon these studies by detecting asymptomatic infections using qPCR, a highly sensitive method with a low limit of detection ( Taylor et al, 2019 ), in participants of all ages and similarly found that asymptomatic infections have a high probability of being quickly followed by symptomatic illness. The increased short-term hazard could reflect misclassification of a ‘pre-symptomatic’ infection that progressed to symptoms as an asymptomatic exposure ( Njama-Meya et al, 2004 ).…”

“…People with positive RDT results were treated with Artemether-Lumefantrine (AL). DBS were processed to detect P. falciparum infections by extracting genomic DNA (gDNA) from DBS and then tested in duplicate for P. falciparum parasites using a duplex real-time PCR (qPCR) assay targeting the P. falciparum pfr364 motif and human -tubulin gene (Plowe et al, 1995;Taylor et al, 2019). From each DBS, 3 individual punches were deposited in a single well of a 96-well deep well plate and extracted with Chelex-100 following Saponin and Proteinase K treatments.…”