Survival analysis of diagnostic assays in Plasmodium falciparum malaria

Abstract

Background: Rapid diagnostic tests (RDT) and real-time PCR (qPCR) assays are sensitive for diagnosing malaria, but because they detect antigen and DNA, respectively, positivity may not reflect active infection. Performance characteristics of RDT and qPCR in Plasmodium falciparum positive specimens were evaluated over time to elucidate duration of positivity following conversion to microscopy negative. Methods:Specimens from patients with at least one specimen that was positive for P. falciparum by microscopy, and at least one specimen that was negative for P. falciparum within a 1-month period were identified. Survival distributions of the diagnostic tests over time were compared. Performance characteristics for each test were calculated.Results: Ninety specimens were included, with 48 initially positive for P. falciparum, and 42 subsequently negative. Of 42 specimens that converted to microscopy-negative following an initial positive, 26 (61.9 %) and 41 (97.6 %) were positive by qPCR and RDT, respectively. Survival curves of microscopy versus qPCR, as well as microscopy vs RDT differed significantly (p = 0.0002 and p < 0.0001, respectively). Compared to microscopy, sensitivity of qPCR was 100.0 % (95 % CI 90.8-100.0 %), and that of RDT was 100.0 % (95 % CI 90.8-100.0 %). Conclusions:Due to slow clearance of circulating antigen and DNA from bloodstream, RDT and qPCR have low positive predictive value for clinically relevant asexual parasitaemia in post-treatment specimens. Thus, microscopy remains the only available malaria diagnostic that can reliably distinguish true asexual parasitaemia from prolonged clearance of antigen and nucleic acid in a convalescing patient.

Detection of Malaria Parasites After Treatment in Travelers: A 12-months Longitudinal Study and Statistical Modelling Analysis

“…In line with our findings, other studies on travelers have reported similar persistence of PCR positivity after curative treatment ( Dakic et al, 2014 , Phuong et al, 2015 ). A duration of positive microscopy and real-time qPCR up to five and 28 days, respectively, was observed in Serbia ( Dakic et al, 2014 ).…”

“…A duration of positive microscopy and real-time qPCR up to five and 28 days, respectively, was observed in Serbia ( Dakic et al, 2014 ). In addition, a study from Canada reports real-time PCR positivity up to 19 days after microscopy turned negative in successfully treated patients, and suggested the slow clearance of parasite DNA from the bloodstream, pointing out the risk of false positive PCR after treatment ( Phuong et al, 2015 ). Moreover, PCR positivity up to 42 days post-treatment has been observed in endemic areas where neither recrudescence nor reinfection were considered as underlying cause for positive PCR, with no further explanation or investigations into the actual cause of the long PCR positivity ( Aydin-Schmidt et al, 2013 ).…”

Detection of malaria parasites after treatment in travelers: A 12-months longitudinal study and statistical modelling analysis

“…A duration of positive microscopy and real-time qPCR up to five and 28 days, respectively, was observed in Serbia (Dakic et al, 2014). In addition, a study from Canada reports realtime PCR positivity up to 19 days after microscopy turned negative in successfully treated patients, and suggested the slow clearance of parasite DNA from the bloodstream, pointing out the risk of false positive PCR after treatment (Phuong et al, 2015). Moreover, PCR positivity up to 42 days post-treatment has been observed in endemic areas where neither recrudescence nor reinfection were considered as underlying cause for positive PCR, with no further explanation or investigations into the actual cause of the long PCR positivity (Aydin-Schmidt et al, 2013).…”

High prevalence of malaria in a non-endemic setting: comparison of diagnostic tools and patient outcome during a four-year survey (2013–2017)

“…RDTs have been developed to detect antigens derived from malaria parasites; such tests often use a dipstick or cassette format, and provide results in 2–15 min offering a useful alternative to microscopy in situations where reliable microscopic diagnosis is not immediately available [ 10 ]. These assays identify parasite antigens such as HRP2, pLDH and pAldolase [ 2 , 11 ] and are routinely implemented due to their simplicity and rapid turnaround time, enabling them to work as a point-of-care diagnostic.…”

“…Currently available devices have also some limitations: batch-to-batch quality variation, species and density determination, persistent positivity, accuracy, and costs [ 12 ]; moreover, false negative results in the presence of high parasitaemia are reported [ 12 ]. The specificity of RDTs can be low, particularly in the setting of persistent antigenaemia post-treatment of P. falciparum infection, as well as non- falciparum species [ 10 ], although newer generation RDTs perform well in diagnosing P. vivax infections [ 15 ]. For all these reasons RDTs may be used in addition to, but not as a replacement for microscopy [ 15 ].…”