CLINICAL-EVALUATION OF A MYCOBACTERIUM-TUBERCULOSIS PCR ASSAY

On the basis of previously published PCR primer sequences, we have des igned a sensitive system for detecting DNA of the Mycobacterium tuberc ulosis complex (MTB) in patient sputum samples which employs a fast an d simplified sample preparation method appropriate for routine diagnos tic testing, In Order to evaluate the accuracy of the PCR assay, we pe rformed a prospective study with 103 patients, comparing PCR results w ith culture results of samples obtained from a parallel culture assay as well as with subsequent culture results. Using two MTB-specific PCR primer systems, we found 48 of 49 tuberculosis (Tb) patients to be PC R positive (PCR sensitivity, 0.98). Sixteen of 54 presumably non-Tb pa tients showed amplifiable MTB DNA (specificity, 0.7). The study demons trates that for diagnostic applications Of MTB PCR two MTB-specific pr imer pairs should be used. MTB infection is extremely unlikely in case s of MTB PCR-negative samples: with our method for the exclusion of ac tive Tb, the validity of one PCR assay seems to be equivalent to those of at least three culturing procedures. Positive PCR results do not n ecessarily reflect active MTB infection, It remains to be shown whethe r positive PCR results in Tb-negative patients mean false-positivity, an early laboratory finding which predicts a subsequent reactivation o f a prior Tb infection, or whether asymptomatic patients may carry PCR -amplifiable MTB DNA without any clinical relevance. It is important t o point out that the validity of PCR results in clinical studies depen ds on the use of contamination controls parallel to all PCR steps and the simplicity of the DNA extraction method as well as on the specific ity of the PCR results.