Application and evaluation of QBC malaria diagnosis in a holoendemic area

Quantitative Buffy Coat Analysis was used in practical diagnosis situations. In the first place, sensitivity and specificity was measured in an active search survey (720 schoolchildren under 10 years of age, in nine field trips) under unfavourable laboratory conditions (onsite school diagnosis being conducted with electricity supplied by a diesel-powered generator). In this group, the QBC-based study revealed sensitivity and specificity ratings of 99.6% and 81.7% respectively. QBC proved 5.5% more sensitive than the thick-film method, but specificity was greater with the latter. QBC returned good results when used in adverse situations, viz., in the absence of air conditioning and with a diesel generator as the only power supply. QBC was used in a passive search survey (hospital group, 618 children) under good laboratory conditions (air conditioning) with patients enrolled in a trial to measure resistance to antimalarial drugs. In this survey we targeted at assessing the efficacy of chloroquine treatment at dose of 25 mg/kg/3 days. QBC proved more sensitive than the thick-film method, detecting - on day 14 of the in vivo test - low parasitaemias that had gone undetected by thick film. Lastly, this study reports on the conversion of QBC readings (parasitaemia per field) into thick-field terms (number of parasites per microliter of blood), with the aim of measuring the degree of recurring parasitaemia.