Time to identify and define non-tuberculous mycobacteria in a tuberculosis-endemic region

To identify and characterise disease caused by non-tuberculous mycobacteria (NTM) in a tuberculosis-endemic region.

A total of 133 NTM isolates cultivated using Mycobacteria Growth Indicator Tube 960 (MGIT 960) plus Löwenstein-Jensen (LJ) and identified using the NAP and PNBA tests were screened to species level using molecular methods. The 360-base pair (bp) region of the rpoB gene was amplified and analysed using an in-house RLBH assay, PCR-RE and sequencing. The clinical significance of all isolated NTM was determined as per published guidelines.

Of the 133 isolates, 127 were confirmed as NTM and six as Mycobacterium tuberculosis complex by molecular methods; 81% of the NTM were recovered from pulmonary and 19% from extra-pulmonary specimens. Among the rapidly growing NTM, M. fortuitum (41%) and M. abscessus (59%) were predominant. Among the slow growing NTM, 40% were identified as M. intracellulare, followed by M. simiae (35%), M. kansasii (6%), M. gordonae (4%) M. szulgai (2%) and M. avium (1%). Mixed infections were noted in 10 (12%) cases. In all, 58 (46%) NTM met clinical, radiological and microbiological criteria and were considered definite NTM infections, 33 (26%) were highly probable disease and 36 (28%) were possible disease or colonisation.

Overall, 72% of isolated NTM were found to be clinically significant. Accurate species identification and adherence to published guidelines help to outline pathogenicity.