Department of Microbiology, The University of Hong Kong, Queen Mary Hospital, Hong Kong

Molecular diagnosis of tuberculosis by Polymerase Chain Reaction (PCR) using different DNA amplification systems was performed on 380 pulmonary and 238 extra-pulmonary specimens (including CSF, Peritoneal fluid, Pericardial fluid, Pleural fluid, Lymph node aspirate and Formalin fixed tissue sections). Three DNA amplification techniques were evaluated: a manual in-house single tube nested PCR [nPCR], the Cobas Amplicor System from Roche Diagnostic Systems [aPCR], and the Abbott LCx Probe System of Abbott Laboratories [aLCx-p]). For pulmonary specimens, the sensitivity of the nPCR, aPCR-h and aLCx-p were 77.1, 84.3 and 77.1% respectively. For extra-pulmonary specimens (except formalin fixed tissue sections), the sensitivity of the nPCR and aPCR were 63.3% and 56.7% respectively. All PCR assays attained a specificity of 100% in direct detection of Mycobacterium tuberculosis in specimens. Inhibitors to PCR were detected in 5% and 13% pulmonary and extra-pulmonary specimens. Pilot study indicated sensitivity of PCR for formalin fixed tissue section was low (less than 50%) especially for amplification of DNA templates longer than 250 base pairs. Results will be discussed in light of selection of DNA extraction protocols and internal controls for PCR applications in diagnostic laboratories.