Malaria rapid diagnostic tests in elimination settings—can they find the last parasite?

Rapid diagnostic tests (RDTs) for malaria have improved the availability of parasite-based diagnosis throughout the malaria-endemic world. Accurate malaria diagnosis is essential for malaria case management, surveillance, and elimination. RDTs are inexpensive, simple to perform, and provide results in 15-20 min. Despite high sensitivity and specificity for Plasmodium falciparum infections, RDTs have several limitations that may reduce their utility in low-transmission settings: they do not reliably detect low-density parasitaemia (≤200 parasites/μL), many are less sensitive for Plasmodium vivax infections, and their ability to detect Plasmodium ovale and Plasmodium malariae is unknown. Therefore, in elimination settings, alternative tools with higher sensitivity for low-density infections (e.g. nucleic acid-based tests) are required to complement field diagnostics, and new highly sensitive and specific field-appropriate tests must be developed to ensure accurate diagnosis of symptomatic and asymptomatic carriers. As malaria transmission declines, the proportion of low-density infections among symptomatic and asymptomatic persons is likely to increase, which may limit the utility of RDTs. Monitoring malaria in elimination settings will probably depend on the use of more than one diagnostic tool in clinical-care and surveillance activities, and the combination of tools utilized will need to be informed by regular monitoring of test performance through effective quality assurance.     

Améliorer la prise en charge du paludisme par les tests de diagnostic rapide (TDR) : appropriation par les prestataires et bénéficiaires de soins au Sénégal

Introduced in the public health services in Senegal since 2007, Rapid Diagnostic Tests (RDTs) are a new technical opportunity for clinical diagnosis of malaria. We analyze how different categories of caregivers, who are the providers, assume appropriation of their professional practices. Similarly, we document, from the analysis of their application for care, attitudes of recipients towards RDTs. The results show a time lag between the uses of this tool and the recommendations. RDTs have a recognized epidemiological usefulness. However, their positive integration requires a change in behaviors that caregivers and recipients are not always willing to assume. Indeed, the architecture, working conditions and applications for care influence the modes of appropriation of this technical innovation.     

Rapid diagnostic tests for non-malarial febrile illness in the tropics

The recent roll-out of rapid diagnostic tests (RDTs) for malaria has highlighted the decreasing proportion of malaria-attributable illness in endemic areas. Unfortunately, once malaria is excluded, there are few accessible diagnostic tools to guide the management of severe febrile illnesses in low resource settings. This review summarizes the current state of RDT development for several key infections, including dengue fever, enteric fever, leptospirosis, brucellosis, visceral leishmaniasis and human African trypanosomiasis, and highlights many remaining gaps. Most RDTs for non-malarial tropical infections currently rely on the detection of host antibodies against a single infectious agent. The sensitivity and specificity of host-antibody detection tests are both inherently limited. Moreover, prolonged antibody responses to many infections preclude the use of most serological RDTs for monitoring response to treatment and/or for diagnosing relapse. Considering these limitations, there is a pressing need for sensitive pathogen-detection-based RDTs, as have been successfully developed for malaria and dengue. Ultimately, integration of RDTs into a validated syndromic approach to tropical fevers is urgently needed. Related research priorities are to define the evolving epidemiology of fever in the tropics, and to determine how combinations of RDTs could be best used to improve the management of severe and treatable infections requiring specific therapy.     

Malaria rapid diagnostic tests in travel medicine

Malaria is a serious condition in the non-immune traveller, and prognosis depends on timely diagnosis. Although microscopy remains the cornerstone of diagnosis, malaria rapid diagnostic tests (RDTs) are increasingly used in non-endemic settings. They are easy to use, provide results rapidly and require no specific training and equipment. Reported sensitivities vary between different RDT products but are generally good for Plasmodium falciparum, with RDTs detecting the P. falciparum antigen histidine-rich protein-2 (PfHRP2) scoring slightly better than P. falciparumlactate dehydrogenase (Pf-pLDH)-detecting RDTs. Sensitivity is lower for Plasmodium vivax (66.0 – 88.0%) and poor for Plasmodium ovale (5.5 – 86.7%) and Plasmodium malariae (21.4 – 45.2%). Rapid diagnostic tests have several other limitations, including persistence of the PfHRP2 antigen, cross-reactions of P. falciparum with the non-falciparum test line and vice versa and (rare) false-positive reactions due to other infectious agents or immunological factors. False-negative results occur in the case of low parasite densities, prozone effect or pfhrp2 gene deletions. In addition, errors in interpretation occur, partly due to inadequacies in the instructions for use. Finally, RDTs do not give information about parasite density. In the diagnostic laboratory, RDTs are a valuable adjunct to (but not a replacement for) microscopy for the diagnosis of malaria in the returned traveller.In malaria endemic settings, special groups of travellers (those travelling for long periods, expatriates and short-stay frequent travellers) who are remote from qualified medical services may benefit from self-diagnosis by RDTs, provided they use correctly stored RDT products of proven accuracy, with comprehensive instructions for use and appropriate hands-on training.     

Limited Level of Accuracy Provided by Available Rapid Diagnosis Tests for Malaria Enhances the Need for PCR-Based Reference Laboratories

The rise of imported malaria cases and the high fatality rate in Europe make the search for new and easy diagnostic methods necessary. Rapid diagnosis tests (RDTs) are, in part, developed to cover the lack of diagnosis experience. Unfortunately, our data suggest that the accuracy of RDTs is insufficient and could increase the number of incorrect malaria diagnoses.     

Current strategies to avoid misdiagnosis of malaria

Malaria remains the most important parasitic disease, and tens of thousands of cases are imported into non-endemic countries annually. However, any single institution may see only a very few cases—this is probably the reason why laboratory and clinical misdiagnosis may not be uncommon. In the laboratory, unfamiliarity with microscopic diagnosis may be the main reason, considering the large number of laboratory staff who provide on-call services, often without expert help at hand, as well as the difficulty in detecting cases with low-level parasitemia. Staff should therefore be provided with continuing microscopic training to maintain proficiency. The complementary use of immunochromatographic rapid detection tests (RDTs) may be useful, especially during on-call hours, although, in order to ensure correct interpretation, their inherent limitations have to be well known. Diagnosis based on the polymerase chain reaction is still unsuitable for routine use, due to its long turnaround time, its cost, and its unavailability outside regular hours, although it may be helpful in selected cases. Once the alert clinician has considered the possibility of malaria, and suspicion continues to be high, malaria can be excluded by repeat smears or RDTs. However, the absence of clinical suspicion may not be infrequent, and may have more serious consequences. Depending on the local number of malaria cases seen, laboratory staff should have a low threshold for the decision to perform unsolicited malaria diagnostic tests on suspicious samples, especially if other laboratory tests are abnormal (e.g. thrombocytopenia, presence of atypical lymphocytes, or raised lactate dehydrogenase). The detection of intraleukocytic hemozoin during automated full blood counts is a promising new way to avoid misdiagnosis of clinically unsuspected malaria.     

Rapid diagnostic tests for the serodiagnosis of human cystic echinococcosis

Cystic echinococcosis (CE) is a parasitic zoonosis especially affecting resource-poor populations in livestock raising areas. Imaging, in particular ultrasound (US), is crucial for the diagnosis, staging, and clinical management of abdominal CE in humans. Serology is a valuable complement to imaging, especially when ultrasound features of CE are absent or unclear. In rural endemic areas, where expertise in US is scant, and conventional serology techniques are unavailable due to lack of laboratory equipment, rapid diagnostic tests (RDTs) may be very useful. Several reports have described the performance of commercial and experimental RDTs in the diagnosis of CE, including a recent study by our group that compared the diagnostic performances of three commercial RDTs for the diagnosis of hepatic CE. To put RDTs for CE in context, we reviewed the available literature in English on this topic. Overall, RDTs appear to be useful in resourcepoor settings where they may replace conventional serodiagnostic tests. However, like other serodiagnostic tests, RDTs lack standardization and show unsatisfactory sensitivity and specificity. An important issue that needs to be addressed is that studies on the diagnostic performance of RDTs fail to take into account the variables known to influence results such as anatomical location and cyst stage.     

Comparative Evaluation of 11 Commercialized Rapid Diagnostic Tests for Detecting Trypanosoma cruzi Antibodies in Serum Banks in Areas of Endemicity and Nonendemicity

Chagas disease is one of the main public health issues in Latin America. Increasingly during the past few decades, Trypanosoma cruzi infection has been detected in North America, Europe, and the Western Pacific, mainly as a result of population movement. The limited availability of rapid serological diagnostic tests hinders rapid diagnosis and early treatment in areas of endemicity and nonendemicity. In collaboration with 11 national reference laboratories (NRLs) from different geographical areas, we evaluated the performances of commercialized serological rapid diagnostic tests (RDT) for T. cruzi infection. Eleven commercialized T. cruzi infection RDTs were evaluated on a total of 474 samples extensively tested with at least three different techniques for Chagas disease, maintained at controlled low temperatures, and stored in the serum banks of the 11 NRLs. We measured the sensitivity, specificity, and concordance of each RDT and provided an additional questionnaire to evaluate its ease of use. The selected RDTs in this study were performed under controlled laboratory conditions. Out of the 11 RDTs, we found 8 of them to be useful, with the cassette format favored over the strip. We did not observe significant differences in RDT performances in the different regions. Overall, the performance results were lower than those disclosed by the manufacturers. The results of this evaluation validate the possibility of using RDTs to diagnose Chagas disease, thereby decreasing the time to treatment at a primary health care facility for patients who are willing to be treated. Further studies should be conducted in the laboratory and in the field to confirm these data, expressly to evaluate reproducibility in resource-limited settings, or using whole blood in clinical settings in areas of endemicity and nonendemicity.     

Evaluation of the ICT malaria P.f/P.v and the OptiMal rapid diagnostic tests for malaria in febrile returned travellers

Rapid diagnostic tests (RDTs) are less reliant on expert microscopy and have the potential to reduce errors in malaria diagnosis but have not been extensively evaluated in nonimmune persons or in countries where infection is not endemic. We evaluated the ICT P.f/P.v (ICT-Amrad, Sydney, Australia) and OptiMal (Flow Inc., Portland, Oreg.) assays prospectively for the diagnosis of malaria in 158 specimens from 144 febrile returned travellers in Australia by using expert microscopy and PCR as reference standards. Malaria was diagnosed in 93 specimens from 87 patients by expert microscopy, with 3 additional specimens from recently treated patients testing positive for Plasmodium falciparum by PCR. For the diagnosis of asexual-stage P. falciparum malaria, the sensitivity and specificity of the ICT P.f/P.v assay were 97 and 90%, respectively, and those of the OptiMal assay were 85 and 96%, respectively. The ICT P.f/P.v assay missed one infection with a density of 45 parasites/ micro l, whereas the OptiMal assay missed infections up to 2,500/ micro l; below 1,000/ micro l, its sensitivity was only 43%. For the diagnosis of P. vivax malaria, the sensitivity and specificity of the ICT P.f/P.v assay were 44 and 100%, respectively, and those of the OptiMal assay were 80 and 97%, respectively. Both assays missed infections with parasite densities over 5,000/ micro l: up to 10,000/ micro l with the former and 5,300/ micro l with the latter. Despite the high sensitivity of the ICT P.f/P.v assay for P. falciparum malaria, caution is warranted before RDTs are widely adopted for the diagnosis of malaria in nonimmune patients or in countries where malaria is not endemic.     

Effect of sequence variation in Plasmodium falciparum histidine- rich protein 2 on binding of specific monoclonal antibodies: Implications for rapid diagnostic tests for malaria

The ability to accurately diagnose malaria infections, particularly in settings where laboratory facilities are not well developed, is of key importance in the control of this disease. Rapid diagnostic tests (RDTs) offer great potential to address this need. Reports of significant variation in the field performance of RDTs based on the detection of Plasmodium falciparum histidine-rich protein 2 (HRP2) (PfHRP2) and of significant sequence polymorphism in PfHRP2 led us to evaluate the binding of four HRP2-specific monoclonal antibodies (MABs) to parasite proteins from geographically distinct P. falciparum isolates, define the epitopes recognized by these MABs, and relate the copy number of the epitopes to MAB reactivity. We observed a significant difference in the reactivity of the same MAB to different isolates and between different MABs tested with single isolates. When the target epitopes of three of the MABs were determined and mapped onto the peptide sequences of the field isolates, significant variability in the frequency of these epitopes was observed. These findings support the role of sequence variation as an explanation for variations in the performance of HRP2-based RDTs and point toward possible approaches to improve their diagnostic sensitivities.     

Prevalence and density-related concordance of three diagnostic tests for malaria in a region of Tanzania with hypoendemic malaria

Accurate malaria diagnosis has dual roles in identification of symptomatic persons for effective malaria treatment and also enumeration of asymptomatic persons who contribute to the epidemiologic determinants of transmission. Three currently used diagnostic tests, microscopy, rapid diagnostic tests (RDTs), and real-time PCR, all have different sensitivities and specificities, which are parasite density dependent. Here, we compare their concordance among 451 febrile episodes in a cohort of 2,058 children and adults followed over 6 months in a region in central Tanzania with hypoendemic malaria. Microscopy, a histidine-rich protein-based RDT, and two different real-time PCR gene probes detected Plasmodium falciparum in 20, 54, 41, and 78 episodes of fever, respectively. They had complete concordance in only 9 episodes. Real-time PCR with an 18S probe was more sensitive than with a mitochondrial probe for cytochrome b despite higher copy numbers of mitochondrial DNA. Both PCR yields were increased 4-fold by glycogen/acetate precipitation with low-speed centrifugation. Duplicate PCR increases low-density malaria detection. RDT had the highest number of unique positives, presumably from persistent antigen despite the absence of parasites, although RDT did not detect 3 parasitemias with over 1,000 parasites/μl. In a latent class analysis, real-time PCR had significantly higher sensitivity than did microscopy or RDT. Agreement between real-time PCR, RDT, and microscopy was highest in March and April, when both the P. falciparum parasite rate and parasite densities are highest. Real-time PCR is more sensitive and specific than RDT and microscopy in low-prevalence, low-parasite-density settings.     

Use of rapid diagnostic tests for diagnosis of malaria in the UK

BACKGROUND: Malaria is currently diagnosed almost exclusively by microscopy in clinical laboratories. The introduction of rapid diagnostic tests (RDTs) may be useful in achieving rapid detection of malaria parasites, especially in situations where malaria is not often seen or where staff are inexperienced. AIM: To explore the use of RDT in UK laboratories. METHODS: The current use of RDTs was surveyed in UK laboratories subscribing to the United Kingdom National External Quality Assessment Scheme blood parasitology and haematology schemes. RESULTS: An overall survey response rate of 60.3% was seen. RDTs were found to be the preferred choice, either alone or in conjunction with microscopy in 31.2% of the samples examined during normal working hours and in 44.3% of the specimens examined on call. CONCLUSIONS: During on-call hours, the use of RDTs was observed to increase and RDTs changed the diagnosis in 12% of laboratories. No established protocol for RDT use was, however, observed in the UK. A protocol that needs to be validated in the laboratory setting is suggested.     

Loop-Mediated Isothermal Amplification Assay for Rapid Diagnosis of Malaria Infections in an Area of Endemicity in Thailand

The loop-mediated isothermal amplification (LAMP) method, developed by our group for diagnosis of four human malaria parasites, was evaluated on a large scale at a remote clinic in Thailand where malaria is endemic. A total of 899 febrile patients were analyzed in this study. LAMP was first evaluated in 219 patients, and the result was compared to those of two histidine-rich protein (HRP)-2 rapid diagnostic tests (RDTs) and microscopy as a gold standard. LAMP DNA extraction was conducted by a simple boiling method, and the test results were assessed visually. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 95.7%, 100%, 100%, and 98%, respectively, for LAMP and 98.6%, 98%, 95.8%, and 99.3%, respectively, for RDTs. Since RDT-positive results were based on one out of two RDTs, the sensitivity of RDTs was slightly higher than that of LAMP. However, LAMP tended to be more specific than RDTs. LAMP next was evaluated in 680 patients, and the result was compared to that of microscopy as a gold standard. Sensitivity, specificity, PPV, NPV, and diagnostic accuracy of LAMP were 88.9%, 96.9%, 92.2%, 95.5%, and 94.6%, respectively. Nested PCR was used to confirm the discrepant results. Malaria LAMP in a remote clinic in Thailand achieved an acceptable result, indicating that LAMP malaria diagnosis is feasible in a field setting with limited technical resources. Additionally, the rapid boiling method for extracting DNA from dried blood spots proved to be simple, fast, and suitable for use in the field.     

Les tests de diagnostic rapide pour le paludisme

The rapid diagnostic tests (RDTs) whose main interest lies in their implementation without special equipment by unskilled personnel have grown significantly over the past fifteen years to diagnose malaria. They rely on the detection of specific Plasmodium proteins, PfHRP2, pLDH and aldolase. If the detection of PfHRP2 has very good sensitivity for the diagnosis of Plasmodium falciparum malaria, the detection of pLDH or aldolase is less efficient for other species, leaving its place to the reference microscopic diagnosis. RDT could not generally be used to monitor therapeutic efficacy because they can remain positive after clinical and parasitological cure. Furthermore, the development of the use of these tests has highlighted the need for quality assurance programs to monitor their production as their use.     

Evaluation du test de diagnostic rapide du paludisme OptiMal-IT® pLDH à la limite de la distribution de <Emphasis Type="Italic">Plasmodium falciparum</Emphasis> en Mauritanie

Performance of the malaria Rapid Diagnostic Test (RDT) OptiMal-IT® was evaluated in Mauritania where malaria is low and dependent on a short transmission season. Slide microscopy was considered as the reference method of diagnosis. Febrile patients with suspected malaria were recruited from six health facilities, 3 urban and 3 rural, during two periods (December 2011 to February 2012, and August 2012 to March 2013). Overall, 780 patients were sampled, with RDT and thick blood film microscopy results being obtained for 759 of them. Out of 774 slides examined, of which 200 were positive, P. falciparum and P. vivax mono-infections were detected in 63.5% (127) and 29.5% (59), while P. falciparum/P. vivax coinfections were detected in 7% (14). Both species were observed in all study sites, although in significantly different proportions. The proportions of thick blood film and OptiMal-IT® RDT positive individuals was 26.3% and 30.3% respectively. Sensitivity and specificity of OptiMal-IT® RDT were 89% [95% CI, 84.7-93.3] and 91.1% [88.6-93.4]. Positives and negative predictive values were 78.1% [72.2-83.7] and 95.9% [94.1-97.5]. These diagnostic values are similar to those generally reported elsewhere, and support the use of RDTs as the main diagnostic tool for malaria in Mauritanian health facilities. In the future, choice of RDTs to be used must take account of thermostability in a hot, dry environment and their ability to detect P. falciparum and P. vivax.     

Rapid diagnostic tests for infectious diseases in the emergency department

BackgroundRapid diagnostic tests (RDTs) for infectious diseases, with a turnaround time of less than 2 hours, are promising tools that could improve patient care, antimicrobial stewardship and infection prevention in the emergency department (ED) setting. Numerous RDTs have been developed, although not necessarily for the ED environment. Their successful implementation in the ED relies on their performance and impact on patient management.ObjectivesThe aim of this narrative review was to provide an overview of currently available RDTs for infectious diseases in the ED.SourcesPubMed was searched through August 2019 for available studies on RDTs for infectious diseases. Inclusion criteria included: commercial tests approved by the US Food and Drug Administration (FDA) or Conformité Européenne (CE) in vitro diagnostic devices with data on clinical samples, ability to run on fully automated systems and result delivery within 2 hours.ContentA nonexhaustive list of representative commercially available FDA- or CE-approved assays was categorized by clinical syndrome: pharyngitis and upper respiratory tract infection, lower respiratory tract infection, gastrointestinal infection, meningitis and encephalitis, fever in returning travellers and sexually transmitted infection, including HIV. The performance of tests was described on the basis of clinical validation studies. Further, their impact on clinical outcomes and anti-infective use was discussed with a focus on ED-based studies.ImplicationsClinicians should be familiar with the distinctive features of each RDT and individual performance characteristics for each target. Their integration into ED work flow should be preplanned considering local constraints of given settings. Additional clinical studies are needed to further evaluate their clinical effectiveness and cost-effectiveness.     

Diagnosis of Plasmoduim falciparum malaria in pregnancy in sub-Saharan Africa: the challenges and public health implications

Plasmodium falciparum malaria in pregnancy is a major public health problem in sub-Saharan Africa and represents enormous diagnostic challenge. The objective of this report was to review scientific data from studies conducted in sub-Saharan Africa on the diagnosis of malaria in pregnancy within the last two decades (1987 to 2007), to highlight the challenges and the public health implications. Using the Medline Entrez-Pubmed search, relevant publications were identified for the review via combinations of key words such as Malaria, Pregnancy, and Sub-Saharan Africa, which yielded 777 entries as of September 2007. The results from the various studies were discordant, due to differences in the techniques of sample collection and analysis, based on the differences in the definition of clinical, peripheral, and placental malaria. Definitions were based on the presence of malaria parasite and/or pigments in blood smear from peripheral/placental blood, on histological placental findings, on the use of rapid diagnostic tests (RDTs) and polymerase chain reaction (PCR). Nonspecific clinical presentation of malaria, lack of efficient diagnostic facilities and trained personnel, and absence of regulatory standards for diagnostic tests, are some of the major diagnostic challenges. Increased allocation of resources to development and application of accurate diagnostics will improve malaria diagnosis in pregnancy.     

Evaluation of rapid diagnostic tests for malaria in Swedish travellers

Rapid diagnostic tests (RDTs) for malaria have become valuable tools for the diagnosis of malaria in both endemic and non-endemic areas. During a 7-year period, first the MalaQuick rapid test and then the NOW Malaria test, were evaluated by well-trained laboratory technicians in a university hospital laboratory of parasitology. A total of 635 blood samples were selected from 4731 blood specimens obtained from travellers at the emergency department, at wards and at out-patient clinics. The samples were analysed by microscopy and RDT. Malaria parasites were detected in the blood films of 134 (21%) samples. The sensitivity of the RDT for Plasmodium falciparum was 97.7% (84 of 86 samples) with a negative predictive value of 99.6%. The two false-negative results were associated with low levels of parasitaemia. For non-falciparum species the sensitivity was only 58.3% (28 of 48 samples). Based on the excellent ability of the RDTs to detect P. falciparum infections, we recommend the use of the NOW Malaria test as a complement to microscopy in the laboratory.