Paracheck-Pf® accuracy and recently treated Plasmodium falciparum infections: is there a risk of over-diagnosis?

Abstract

BackgroundAn assessment of the accuracy of Paracheck Pf®, a malaria rapid diagnostic test (RDT) detecting histidine rich protein 2 was undertaken amongst children aged 6–59 months in eastern Democratic Republic of Congo.MethodsThis RDT assessment occurred in conjunction with an ACT efficacy trial. Febrile children were simultaneously screened with both RDT and high quality microscopy and those meeting inclusion criteria were followed for 35 days.Results358 febrile children were screened with 180 children recruited for five weeks follow-up. On screening, the RDT accurately diagnosed all 235 true malaria cases, indicating 100% RDT sensitivity. Of the 123 negative slides, the RDT gave 59 false-positive results, indicating 52.0% (64/123) RDT specificity. During follow-up after treatment with an artemisinin-based combination therapy, 98.2% (110/112), 94.6% (106/112), 92.0% (103/112) and 73.5% (50/68) of effectively treated children were still false-positive by RDT at days 14, 21, 28 and 35, respectively.ConclusionResults show that though the use of Paracheck-Pf® is as sensitive as microscopy in detecting true malaria cases, a low specificity did present a high frequency of false-positive RDT results. What's more, a duration of RDT false-positivity was found that significantly surpassed the 'fortnight' after effective treatment reported by its manufacturer. Though further research is needed in assessing RDT accuracy, study results showing the presence of frequent false positivity should be taken into consideration to avoid clinicians inappropriately focusing on malaria, not identifying the true cause of illness, and providing unnecessary treatment.

Accuracy of Two Malaria Rapid Diagnostic Tests (RDTS) for Initial Diagnosis and Treatment Monitoring in a High Transmission Setting in Uganda

“…20 However, gametocytes were not found to significantly affect duration of antigenemia in other assessments. 10,11 In this study the gametocyte rate of 4% in patients who were followed up was too low to identify a significant correlation with the duration of antigenemia. Other studies using molecular methods to identify gametocytes have suggested that microscopy dramatically underestimates gametocytemia.…”

“…This implies that persistent antigenemia of HRP2 in these patients contributed to the low specificity of the HRP2-based RDT, as suggested by previous studies. 10,11 Another factor that contributes to false-positive HRP2 results is sub-patent parasitemia, i.e., presence of parasite density levels below the detection threshold for expert microscopy of 10-50 parasites/ μL. 8,19 A study done at sites of varying malaria transmission intensity in Uganda found up to 45% of samples that were negative for malaria by microscopy to be positive by PCR at the site with the highest transmission rate.…”

“…Persistent antigenemia of HRP2 has been shown for up to 28-42 days after successful treatment and clearance of malaria parasites in peripheral blood. 10,11,13 Although the mechanism of HRP2 clearance is not well understood, some features that appear to be associated with its persistence after efficacious treatment include high pretreatment parasite density, presence of subpatent parasitemia, and presence of gametocytes, which continue to secrete antigen. In this study, children with a higher pretreatment parasite density had longer duration of persistent HRP2 antigenemia.…”

“…8,9 However, HRP2 antigen remains in the bloodstream for several weeks after parasite clearance, thus contributing to false-positive results and limiting specificity. [10][11][12][13][14] The pLDH-based assays may be more useful for monitoring patients' recovery after treatment and avoiding unnecessary retreatment of malaria because they turn negative soon after parasite clearance from the blood. 15 Additional information on RDT performance in high transmission areas will be helpful in guiding policy and practice.…”

False-Negative Rapid Diagnostic Tests for Malaria and Deletion of the Histidine-Rich Repeat Region of the hrp2 Gene †

“…These results suggest that the majority of persons with P. falciparum infection are positive using HRP2-based RDTs (454/480 ¼ 95%) and thus, that HRP2-based RDTs are likely to be valuable, especially in regions where skilled microscopists are rare. However, the false-negative HRP2-based RDTs obtained for a minority (5%) of smear-positive specimens indicate that a negative test result with an RDT based on HRP2 (e.g., 3,[20][21][22][23][24][25][26] does not exclude active bloodstream infection with asexual P. falciparum parasites. In addition, the association between false-negative RDTs and a low MOI suggests that this discrepancy may become increasingly important as malaria control becomes more effective.…”