Evaluation of Fluorotype MTB for detection of Mycobacterium tuberculosis complex DNA in clinical specimens from a low-incidence country

Abstract

Background: With Fluorotype MTB (FT MTB, HAIN Lifesciences, Germany) a new semi-automated assay for detection of M. tuberculosis complex (MTBC) in clinical specimens has been introduced. In a prospective study, we evaluated the diagnostic performance of FT MTB in a routine diagnostic setting in a low-incidence country.

Methods: A total of 1039 respiratory specimens received for routine mycobacteriology diagnostics were analysed by FT MTB. Results were compared to those of culture, microscopy and clinical diagnosis. 61 specimens were excluded from further analysis due to bacterial contamination of cultures.

Results: FT MTB detected 52 of 59 TB specimens (45 culture-positive with MTBC, 7 with clinical diagnosis of TB). With 902 of 912 non-TB specimens (884 culture-negative, 18 with growth of non-tuberculous mycobacteria) FT MTB was negative; discrepant positive FT MTB results were found with 10 specimens. Overall sensitivity, specificity, positive and negative predictive values were 88.1%, 98.9%, 83.8% and 99.2%. Sensitivity rates for smear-positive and smear-negative TB specimens were 100% and 56.3%, respectively. Seven of 978 samples (0.7%) yielded invalid FT MTB results.

Conclusions: FT MTB is a new accurate, half automated assay for rapidly diagnosing TB and suitable for larger series of samples. Performance characteristics were found to be similar to those of other commercial NAATs. Its sensitivity in paucibacillary, smear-negative specimens and its utility for TB diagnostics in high-incidence settings needs to be addressed in further studies.

Figure 1

Comparison of false-positive and true-positive results. MTBC-specific melting curve peak values for false-positive (left, n = 10) and true-positive (right, n = 52) FT MTB results are shown. Boxes in grey (false-positive) and white (true-positive) represent means of values ± standard deviation, respectively. Maximum and minimum values are depicted by vertical lines. Dotted lines show median values.