EVALUATION OF THE QBC METHOD TO DETECT MALARIA INFECTIONS IN-FIELD SURVEYS

The conventional peripheral blood film method used to diagnose malaria is characterized by low sensitivity in scanty parasitaemia and can be time consuming when required to rule out infection. The Quantitative Buffy Coat (QBC) method has been proposed to be quicker and more sensi tive. We conducted a malaria survey in April 1992 among school-childre n in Kisumu (holoendemic) and Webuye (hypoendemic) areas of Western Ke nya. Peripheral blood samples were examined by thick blood smear (TBS) stained with Giemsa solution, and by the QBC method. A total of 360 p aired samples were analyzed. There were 175 (49%) positive TBS and 201 (56%) positive QBC. Of the 185 TBS classified as negative, 30 (16%) w ere positive by QBC. When parasite density by TBS was greater-than-or- equal-to 100/300 WBCs, the sensitivity of QBC was 100%. Overall sensit ivity for QBC was 98%, with a specificity of 84%. Negative predictive value for the QBC was 98%, and had a calculated accuracy of 92%. It to ok an average of 44 minutes to process a TBS and a further average of 2.6 minutes to examine a negative TBS. For the QBC the mean time to pr ocess and to examine was 7.09 and 1.04 minutes respectively. We conclu de that the QBC is quicker, with high sensitivity, and will prove usef ul in clinical and epidemiological screening, especially when parasita emia is low.