Molecular Testing for Plasmodium falciparum by Use of Serum or Plasma and Comparison with Microscopy and Rapid Diagnostic Testing in Febrile Nigerian Patients

Abstract

c Plasmodium nucleic acids have been detected in serum and plasma, but there is little published data describing the diagnostic performance of malaria nucleic acid amplification tests (NAATs) using these specimen types. Previously, our group described a multiplex NAAT for the detection of dengue virus, Leptospira, and Plasmodium species with a callout for P. falciparum (the DLM assay) that demonstrated sensitive detection of P. falciparum from plasma samples during initial evaluation. In this study, we evaluated the sensitivity and specificity of P. falciparum detection in febrile Nigerian patients using the DLM assay, microscopy, and a rapid diagnostic test (BinaxNOW Malaria). Assay performances were compared using a composite reference, which was considered positive if malaria was detected by two or more methods. Serum (n ‫؍‬ 182) or plasma (n ‫؍‬ 148) from 317 patients was tested; the average sample volume was 70 l (range, 5 to 300 l). The sensitivity and specificity of the DLM assay were 97.1% and 93.5%, respectively. The sensitivity of the malaria rapid diagnostic test (98.1%) was similar to that of the DLM assay, and both proved significantly more sensitive than microscopy (79%; P < 0.0001). When analysis was limited to samples with >75 l of serum or plasma, the sensitivity of the DLM assay improved to 99% and specificity was 97.5%. For P. falciparum cases, cycle threshold values in the DLM assay correlated with the parasite density detected by microscopy (Spearman's rank correlation coefficient, P < 0.0001). In conclusion, malaria detection using the DLM assay on serum or plasma is more sensitive than and equal in specificity to microscopy in patients with P. falciparum malaria.T he entirety of Nigeria is considered an area of moderate to high malaria transmission by the WHO (Ն1 case per 1,000 residents), and virtually all cases result from infection with Plasmodium falciparum, the most common cause of severe malaria (1). Despite the high prevalence of malaria in Nigeria, there is concern that it is overdiagnosed in patients presenting with an undifferentiated systemic febrile illness (2). While traditional microscopy remains the primary malaria diagnostic method worldwide, malaria rapid diagnostic tests (mRDTs) are also being deployed for confirmation of suspected malaria cases. However, nucleic acid amplification tests (NAATs) for malaria, which have proven more sensitive than microscopy or mRDTs, are not routinely performed (3, 4). Therefore, it is possible that estimates of overtreatment may be inflated due to the relatively poor sensitivity of microscopy for malaria diagnosis. Although Plasmodium nucleic acids have been detected in serum and plasma, there is little published data describing the performance of malaria NAATs using these specimen types (4-7). Rather, most studies have used whole blood or dried blood spots (DBS) (8-12). While whole blood and DBS provide ample amounts of Plasmodium nucleic acids, they present significant challenges for (i) long-term storage and/or (ii) nucleic acid extrac...

Malaria and Chikungunya Detected Using Molecular Diagnostics Among Febrile Kenyan Children

“…Studies that compare the sensitivity of microscopy to molecular testing in symptomatic patients frequently document only a small number of discrepant samples [ 26–30 ], and few studies have documented a significant increase in case detection using molecular methods [ 10 , 31 , 32 ]. This suggests that molecular testing may only result in a small increase in malaria diagnoses and precludes an evaluation of malaria cases diagnosed only by molecular methods.…”

“…Limitations to the current study include the use of only acute-phase serum samples for testing. Although this specimen type is used less often than whole blood for the molecular detection of malaria, we have previously documented the clinical sensitivity and specificity of malaria detection in serum or plasma [ 3 , 10 ]. It is also possible that children presented with symptomatic CHIKV and/or DENV infections but were no longer viremic.…”

“…Malaria is frequently the clinical diagnosis for Kenyan children who present with an acute, undifferentiated fever, and microscopy on thick and thin blood smears remains in wide use for laboratory confirmation, although this method has well documented limitations [ 8 , 9 ]. Molecular testing has proven to be more sensitive than microscopy for the detection of Plasmodium species [ 8 , 10 , 11 ], although most studies that report a significant increase in Plasmodium detection have used whole-blood samples and focused on surveillance testing in asymptomatic individuals [ 11–14 ]. Our group, among others, has reported on the use of serum for malaria detection by real-time PCR (rtPCR) [ 10 , 15 , 16 ].…”

“…Molecular testing has proven to be more sensitive than microscopy for the detection of Plasmodium species [ 8 , 10 , 11 ], although most studies that report a significant increase in Plasmodium detection have used whole-blood samples and focused on surveillance testing in asymptomatic individuals [ 11–14 ]. Our group, among others, has reported on the use of serum for malaria detection by real-time PCR (rtPCR) [ 10 , 15 , 16 ]. In a study of 317 symptomatic patients from Nigeria, malaria rtPCR using serum or plasma proved to be significantly more sensitive than microscopy for the detection of Plasmodium falciparum , without a significant decrease in specificity [ 10 ].…”

“…Our group, among others, has reported on the use of serum for malaria detection by real-time PCR (rtPCR) [ 10 , 15 , 16 ]. In a study of 317 symptomatic patients from Nigeria, malaria rtPCR using serum or plasma proved to be significantly more sensitive than microscopy for the detection of Plasmodium falciparum , without a significant decrease in specificity [ 10 ]. It is notable that this method, which is the same assay used in the current study, demonstrated similar sensitivity to the BinaxNOW Malaria rapid diagnostic test (Alere) with a trend toward improved specificity [ 10 ].…”