Five year experience with thin layer agar medium for rapid diagnosis of tuberculosis.

Abstract

Tuberculosis represents a public health problem worldwide, mainly in developing countries where 95% of the cases occur. New technologies that support rapid diagnosis are not available in these settings because of high cost. New, rapid, and less expensive techniques are necessary before diagnosis can be improved in these areas. The present work compared the performance of a rapid and costly culture media, thin layer agar (CD7H11), with the traditional Lowenstein-Jensen (LJ) culture method. For this comparison, 1,809 clinical specimens were processed for diagnosis of mycobacterial infections. Clinical samples were processed according to standard procedures and cultured concomitantly in LJ and CD7H11. The times required to obtain an isolate were compared for culture media. Sensitivity (S), specificity (Sp), predictive values (PPV, NPV) and agreement (kappa coefficient) were calculated for CD7H11, with LJ serving as the gold standard. CD7H11 showed S to be 73.5% (C.I.95%: 69.6-80.4), Sp to be 99.2% (C.I.95%: 98.8-99.6), PPV 90.4% (C.I.95%: 85.3-95.6) and NPV 97.6% (C.I.95%: 96.8-98.3). Agreement had a kappa coefficient of 0.52. The mean time for CD7H11 was 11 days (SD+/-4.9) compared with 26.5 (SD+/-8.6) days for LJ. Similar results were obtained in a comparison of respiratory and multibacillary clinical samples. In extrapulmonary samples and those with lowered bacillus count, CD7H11 demonstrated a lower sensitivity. The concomitant use of both culture media enhanced sensitivity of detection. CD7H11 proved a simple and rapid technique for culturing mycobacteria and can be combined with traditional methods for improving laboratory capability for diagnosis of tuberculosis.