[Efficacy of bactec TB in the rapid confirmatory diagnosis of mycobacterial infections. A lebanese tertiary care center experience]

ABSTRACT

Rapid detection of Mycobacterium tuberculosis [MTB], especially multidrug-resistant strains, is of importance for prompt clinical management and initiation of public health control measures. Culture remains the "gold" standard in the confirmatory laboratory diagnosis of mycobacterial infections. The reliability of the automated radiometric BACTEC 460 TB [BAC, TEC] system for the rapid detection of mycobacteria in clinical specimens was evaluated and compared to the conventional culture on Lowenstein-Jensen [LJ] medium. All clinical specimens submitted for mycobacterial culture were processed and simultaneously cultured on both BACTEC broth medium and Li solid medium. Acid-fast bacilli [AFB] smears were also performed on the sediments. Differentiation of mycobacterial isolates as MTB or Mycobacterium sp. other than tuber-culosis [MOTT] was based on the BACTEC NAP test. All positive culture findings recovered between January 1997 and December 2003 were analyzed in this study.A total of 3300 specimens were tested of which 355 [10.7%] yielded positive cultures consisting of 233 [65.6%] MTB and 122 [34.4%] MOTT. The percentages of AFB smear-positive were 45% and 49% in clinical speci-mens yielding MTB and MOTT, respectively. Though several types of specimens were cultured, most isolates [72% of MTB and 91% of MOTT] were recovered from respiratory specimens. Overall, the BACTEC showed significantly higher mycobacteria recovery rate [91%] than LJ [77%]. In terms of times to detection, BACTEC showed significantly shorter detection time of isolates than L.1 for the overall [mean 9.6 days for BACTEC vs 22.8 days for Li] and for each category of AFB smear finding. The detection time is shortened for BACTEC with the increasing grade of smear positivity. BACTEC is substantially more sen-sitive, efficient and rapid than LJ in the laboratory diagnosis of mycobacterial infections. This system also provides rapid differentiation of MTB from MOTT and susceptibility test results on MTh. However, the simultaneous use of BACTEC and LJ is recommended to provide maximum optimal recovery of isolates from clinical specimens. The time-saving in BACTEC provides an excellent facility for physicians in patient management and to public health personnel for prompt initiation of infection control measures: