Abstract
BackgroundIn most resource-poor settings, malaria is usually diagnosed based on clinical signs and symptoms and not by detection of parasites in the blood using microscopy or rapid diagnostic tests (RDT). In population-based malaria surveys, accurate diagnosis is important: microscopy provides the gold standard, whilst RDTs allow immediate findings and treatment. The concordance between RDTs and microscopy in low or unstable transmission areas has not been evaluated.ObjectivesThis study aimed to estimate the prevalence of malaria parasites in randomly selected malarious areas of Amhara, Oromia, and Southern Nations, Nationalities and Peoples' (SNNP) regions of Ethiopia, using microscopy and RDT, and to investigate the agreement between microscopy and RDT under field conditions.MethodsA population-based survey was conducted in 224 randomly selected clusters of 25 households each in Amhara, Oromia and SNNP regions, between December 2006 and February 2007. Fingerpick blood samples from all persons living in even-numbered households were tested using two methods: light microscopy of Giemsa-stained blood slides; and RDT (ParaScreen device for Pan/Pf).ResultsA total of 13,960 people were eligible for malaria parasite testing of whom 11,504 (82%) were included in the analysis. Overall slide positivity rate was 4.1% (95% confidence interval [CI] 3.4–5.0%) while ParaScreen RDT was positive in 3.3% (95% CI 2.6–4.1%) of those tested. Considering microscopy as the gold standard, ParaScreen RDT exhibited high specificity (98.5%; 95% CI 98.3–98.7) and moderate sensitivity (47.5%; 95% CI 42.8–52.2) with a positive predictive value of 56.8% (95% CI 51.7–61.9) and negative predictive value of 97.6% (95% CI 97.6–98.1%) under field conditions.ConclusionBlood slide microscopy remains the preferred option for population-based prevalence surveys of malaria parasitaemia. The level of agreement between microscopy and RDT warrants further investigation in different transmission settings and in the clinical situation.
Highlights
In most resource-poor settings, malaria is usually diagnosed based on clinical signs and symptoms and not by detection of parasites in the blood using microscopy or rapid diagnostic tests (RDT)
Blood slide microscopy remains the preferred option for population-based prevalence surveys of malaria parasitaemia
ParaScreen is an immunochromatographic test that detects the presence of pan malaria specific antigen for the detection of all non-falciparum malarial parasites whereas the detection of P. falciparum utilises recognition of specific histidine rich protein-2 (HRP-2)
Summary
In most resource-poor settings, malaria is usually diagnosed based on clinical signs and symptoms and not by detection of parasites in the blood using microscopy or rapid diagnostic tests (RDT). In population-based malaria surveys, accurate diagnosis is important: microscopy provides the gold standard, whilst RDTs allow immediate findings and treatment. The concordance between RDTs and microscopy in low or unstable transmission areas has not been evaluated. About 75% of the total area of the country is malarious, with more than two thirds of the total population estimated to be at risk of infection [1,2]. Malaria transmission in Ethiopia is seasonal, depending mostly on altitude and rainfall. The two main seasons for transmission of malaria in Ethiopia are September to November, sometimes extended to December after heavy summer rains, and March to May, after the light rains [35]. In Ethiopia, Plasmodium falciparum and Plasmodium vivax account for about 60% and 40% of infections, respectively, during the peak transmission period [3,10]
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