European Society of Mycobacteriology - Instituto Nacional de Saúde ...

PP-69
EVALUATION OF A NEW REAL-TIME PCR KIT FOR
THE DIAGNOSIS OF TUBERCULOSIS INRESPIRATORY SPECIMENS
Causse, M; Gutierrez-Aroca, JB; Casal, M
Mycobacteria Reference Center. Microbiology Department. Reina Sofia University Hospital, Cordoba (Spain)
Introduction
Early diagnosis of tuberculosis is one of the major objectives of the World Health Organization. In its latest update, the
Center for Disease Control and Prevention (CDC) recommends the use of a rapid molecular diagnostic technique on
at least one sample per patient.
Objectives
To evaluate a new kit (COBAS Taqman MTB®, Roche) for the diagnosis of tuberculosis in respiratory samples, and compare
results with those obtained by the COBAS Amplicor MTB kit. Culturing (Lowenstein-Jensen or BACTEC MGIT
960) was used for reference purposes.
Material and methods
A total of 170 respiratory and 19 non-respiratory samples were processed. Specimens decontaminated were stained
with auramine and cultured. A single manual extraction was performed using the AMPLICOR Respiratory Specimen
Preparation Kit; eluate aliquots were then amplified using the COBAS Amplicor MTB and the COBAS TaqMan MTB kit.
Automatic sample extraction was also performed, using the Ampliprep TNAI kit, 200-µl aliquots being previously incubated
at 95ºC for 15 minutes.
Results
All 77 smear-positive samples were classified as positive by both kits.
Of the 170 respiratory samples tested using the TaqMan, 2 false positives (FP) and one false negative (FN) were recorded.
Of the 169 tested using the Amplicor kit, there were 2 FP (different samples than TaqMan) and 2 FN.
TaqMan amplification with automatic extraction yielded one false negative and no false positives.
Real-time PCR sensitivity and specificity were 98.7% and 97.7% respectively. Use of TaqMan with automatic extraction
yielded 98.8% sensitivity and 100% specificity. Kappa indices were 0.95 and 0.97 with respect to the comparator.
For smear-negative samples, sensitivity declined to 80% and specificity remained at 97% for the TaqMan kit.
For the 19 non-respiratory specimens, all three techniques tested recorded one false negative.
Conclusions
TaqMan MTB kit is a real-time PCR method offering the same reliability as the Amplicor MTB kit. TaqMan MTB kit appeared
to display good sensitivity using non-respiratory specimens.
It cuts down time-to-results from 6 to 2.5 hours
Automatic extraction reduced the number of false positives and considerably shortened handling time.
European Society of Mycobacteriology | 30 th Annual Congress | July 2009 | Porto - Portugal
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