Doubled Nontuberculous Mycobacteria Isolation as a Consequence of Changes in the Diagnosis Algorithm

Abstract

Background

Nontuberculous mycobacteria (NTM) and their associated diseases remain neglected. Through minor modifications in our diagnostic algorithm, we observed an unexpected higher number of cultivable NTM isolates. Therefore, a retrospective study was performed thoroughly to investigate the effect of changed laboratory procedures on NTM isolation in a specialized tuberculosis hospital.

Methods

NTM isolation rates and composition of NTM species were compared for the two diagnostic algorithms: (1) by using traditional p-nitrobenzoic acid (PNB) selective medium as a preliminary test to identify NTM isolates among the positive cultures (procedure I) and (2) by using the MPT64 antigen detection method to distinguish between Mycobacterium tuberculosis complex (MTBC) isolates and possible NTM isolates after a positive MGIT960 liquid culture (procedure II).

Results

The NTM isolation rate in procedure II was significantly higher than the procedure I (18.08% vs 9.71%; P<0.001). A noticeable increase in the ratio of NTM isolates among the identified mycobacteria was observed over the studied years (ie, from 58.18% in 2019 to 72.93% in 2021), which indicated a more precise prescription of species identification test after prompt information was provided in procedure II. In addition, the consistency of the identified species using multiple specimens from the same patient did not present a significant difference between the procedures.

Conclusion

According to our study, NTM infection might be far more underestimated than it is. A diagnostic procedure combining MGIT960 culture and MPT64 antigen detection could timely and easily identify clues of NTM isolates and improve the diagnosis of NTM infections.

Keywords:

• tuberculosis
• nontuberculous mycobacteria
• p-nitrobenzoic acid
• MPT64 antigen
• species

Abbreviations

NTM, nontuberculous mycobacteria; MTBC, Mycobacterium tuberculosis complex; PNB, p-nitrobenzoic acid; TB, tuberculosis; L-J, Lowenstein–Jensen; AFB, acid-fast bacilli; DST, drug susceptibility testing; BALF, bronchoalveolar lavage fluid; PTB, pulmonary TB.

Role of Sponsors

The sponsor had no role in the design of the study, the collection, and analysis of the data, or the preparation of the manuscript.

Disclosure

The authors declare no conflict of interest.

Additional information

Funding

This study was supported by the Natural Science Fund of China (82072328), Capital’s Funds for Health Improvement and Research (CFH2020-4-2163), Beijing Municipal Administration of Hospitals Ascent Plan (DFL20181602), Beijing Hospitals Authority Youth Programme (QML20201601), and Tongzhou “Yun He” Talent Project (YHLD2019001 and YHLD2018030).