Prompt and accurate diagnosis followed by effective treatment is currently the main malaria control strategy besides preventive measures. Widespread documented resistance to the older common anti-malarial mono-therapies, notably chloroquine, has led to an increased use of the highly effective artemisinin-based combination therapy (ACT) as the first-line treatment for uncomplicated Plasmodium falciparum malaria [1, 2].
Accurate confirmation of malaria diagnosis can reduce the overuse of ACT treatment and, therefore, delay the development of resistance. Moreover, it may both reduce the risk of adverse drug reactions due to unnecessary treatment and increase correct treatment for pathologies other than malaria. This, in turn, increases patient and parents/caretakers confidence in health services by providing accurate information for a proper diagnosis [3, 4]. Currently, the most commonly accepted gold standard diagnostic method is microscopic reading of a stained blood film. This requires laboratory technicians with training and technical expertise, good quality reagents, a well-maintained microscope and is time consuming. From experience it is challenging to have microscopic results in less than two hours, as recommended by WHO, even with well-trained staff. In many populations where malaria is prevalent, no laboratory facilities and/or trained staff are present, making access to microscopically confirmed diagnosis impossible. An alternative to microscopy is to use a rapid diagnostic test (RDT). Malaria RDT technology is attractive to health care settings lacking in human resources especially facing a high caseload of patients with suspected malaria, often including a high proportion of children under five years of age. These tests can be used by personnel including laypersons, and not necessarily laboratory technicians, after limited training. Malaria RDT results are on average available in less than 30 minutes.
The two types of RDT most often used belong to two groups according to the detected antigens: those detecting histidine-rich protein II (HRP2) and those detecting parasite specific lactate dehydrogenase (pLDH).
HRP2 antigen is one of the three histidine-rich proteins produced solely by trophozoites and young gametocytes of Plasmodium falciparum. RDTs based on the detection of HRP2 can only diagnose Plasmodium falciparum infections and thus cannot be used for the detection of Plasmodium vivax or other human malarias (Plasmodium ovale, Plasmodium malariae, and Plasmodium knowlesi, the latter only recently be detected in Asia ).
The malaria RDT most commonly used in the field by Médecins Sans Frontières (MSF) at present is Paracheck-Pf®, which belongs to the HRP2 group. Paracheck-Pf® has widely proven its field reliability to detect Plasmodium falciparum in various continents, countries and settings [i.e. [6–8]]. However, a limitation of HRP2-based tests is their persistent false positivity after effective treatment of the infection. HRP2 is only slowly eliminated from the blood stream as it is expressed in the erythrocyte membrane . This fact renders inconclusive a positive RDT result with a history of a recently treated infection, especially in areas of high transmission [i.e. [10–13]].
This is less of a problem with the pLDH- based tests. PLDH is an intracellular metabolic enzyme produced by all Plasmodium species that infect humans and is produced by sexual and asexual stages of the parasites. PLDH is cleared more quickly from the bloodstream than HRP2 after starting an effective treatment, as it is an enzyme only produced by viable parasites [i. e. [12, 14–16]]. However, production of pLDH from gametocytes after elimination of asexual stages means some tests will still stay falsely positive for several days . As pLDH-based tests are able to detect all human related Plasmodium, these RDTs could reduce the chance of patients being treated unnecessarily for diseases other than malaria or leave non-falciparum malaria untreated as it would be the case with a HRP2-based test.
Unfortunately, to date, the sensitivity of these tests, under field conditions (mainly using the OptiMal-IT test), has often been reported as lower than their HRP2 counterparts and falling below the internationally recommended standard of 90% [8, 18, 19]. However, two recent studies have shown more promising results with sensitivities over 90% demonstrated with CareStart™ two-line PAN-pLDH and CareStart™ three-line P.f/PAN-pLDH tests [12, 20].
This study evaluated CareStart™ three-line P.f/PAN-pLDH test in comparison to Paracheck-Pf®. CareStart™ three-line P.f/PAN-pLDH was chosen for three reasons.
First, CareStart™ three-line P.f/PAN-pLDH is able to detect falciparum malaria as well as non-falciparum malaria. In a region where falciparum malaria is predominant but other species are also present, this test may contribute to a more differentiated diagnosis of malaria.
Second, pLDH-based tests are cleared more rapidly from the blood [12, 14–16]. In regions with high malaria transmission, it is especially important that RDTs can be relied upon to test for new malaria infections shortly after effective treatment of the initial diagnosis.
Third, among pLDH-based tests CareStart™ recently showed its capacity to reach a sensitivity of over 90% [12, 20].
Paracheck-Pf® was chosen for comparison since it is currently in use in the MSF project in Sierra Leone and is considered to have a high sensitivity for Plasmodium falciparum [6–8, 21]. Nevertheless, it has a relatively long false positivity of the test after effective treatment of the patient and only detects falciparum malaria [i.e. [11–21]].
There is an ongoing debate whether or not anti-malarial treatment should be given to children under five years of age only on the basis of clinical suspicion for malaria [4, 22–24]. There is a trend towards laboratory-confirmed, usually RDT based, diagnosis [3, 4]. However, due to the lack of evidence, opinions vary broadly. So far sensitivity and specificity studies for malaria RDTs, with one exception in the Democratic Republic of Congo , did not focus on children under five years of age. Operational research is urgently needed to provide evidence for the use of malaria RDTs in this age class.
The two main aims of the study were 1) to compare the sensitivity and specificity of CareStart™ three-line P.f/PAN-pLDH test and Paracheck-Pf® to diagnose Plasmodium falciparum malaria in children under five years of age using Giemsa-stained blood smears as gold standard reference and 2) to assess the time required for false-positive CareStart™ three-line P.f/PAN-pLDH tests to become negative after successful treatment with ACT.
Secondary aims included assessing ease of use and inter-reader agreement of both malaria RDTs.