[Evaluation of the QBC system for the diagnosis of malaria]

There are currently two methods for the direct diagnosis of malaria: the thin blood smear and the thick blood smear. A third cytological method, called the QBC malaria test (QBC), has been developed. The first studies comparing the three methods report conflicting results. Thus, there is a need for a study of the three methods in parallel and to evaluate the logistic factors which have not been previously assessed. In an analysis of imported malaria, one worker performed the three tests, blind, in parallel with each of 813 samples. The following values were determined: intrinsic validity; predictive values, species diagnostic power; and logistic factors. QBC had the following characteristics: sensitivity = 93.8%; specificity = 99.8%; positive predictive value = 99.3%; negative predictive value = 98.3%; correct species diagnosis = 91.3%; time required for test = 3.7 +/- 0.1 min; storage of tubes at +4 degrees C in the dark = 50 days; cost per test = 27.3 FF (as compared to 24 FF for thin smear and 17.3 FF for thick smear). Although unsuitable for use in countries where malaria is endemic, other than for some specialised situations, QBC is valuable for the diagnosis of imported malaria. In view of our findings, we suggest the following approach to diagnosis: use of the QBC and thin smear tests in parallel first reading the QBC result, as positivity contributes to reading the thin smear result for confirmation of species diagnosis and assessment of parasitaemia.