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Am. J. Trop. Med. Hyg., 55(5), 1996, pp. 485-489
Copyright © 1996 by The American Society of Tropical Medicine and Hygiene

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Comparison of Two Methods for Enumerating Malaria Parasites in Thick Blood Films

Eskild Petersen, N. T. Marbiah, Laura New AND Adam Gottschau
Laboratory of Parasitology, and Department of Biostatistics, Statens Seruminstitut, Copenhagen, Denmark; Department of Epidemiology and Population Sciences, London School of Hygiene and Tropical Medicine, London, United Kingdom; European Community Malaria Control Project, Bo, Sierra Leone

Calculation of parasite densities is important for estimating herd immunity to malaria, and for determining end points in field trials for interventions such as malaria vaccines, impregnated bed nets, and chemosuppression. Two methods of enumeration were compared: method 1, in which 100 consecutive high-power fields (HPFs) are examined, and if they all contain at least one parasite, the number per field is then counted in 10–100 of these fields according to density; and method 2, in which the actual number of parasites present in 100 consecutive fields are counted. The first method significantly underestimates parasite density in samples in which less than all high-power fields are parasite-positive. A correction of method 1 is suggested, which results in a parasite density, which is comparable with that obtained using method 2. The correction factor estimated was 2(- ln(1 - p)), where p is the proportion of positive HPFs. The correction factor presented will allow accurate estimate of parasite densities per volume of blood even if only the proportion of parasite-positive high-power fields containing at least one parasite are counted.




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C. Wongsrichanalai, M. J. Barcus, S. Muth, A. Sutamihardja, and W. H. Wernsdorfer
A Review of Malaria Diagnostic Tools: Microscopy and Rapid Diagnostic Test (RDT)
Am J Trop Med Hyg, December 1, 2007; 77(6_Suppl): 119 - 127.
[Abstract] [Full Text] [PDF]


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Copyright © 1996 by the American Society of Tropical Medicine and Hygiene.