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

Area of Science:

• Clinical microbiology
• Infectious diseases
• Mycobacterial diagnostics

Background:

• Nontuberculous mycobacteria (NTM) and associated diseases are often overlooked in clinical practice.
• Modifications to diagnostic laboratory procedures unexpectedly led to a higher recovery of NTM isolates.
• A retrospective study was initiated to evaluate the impact of altered laboratory protocols on NTM isolation rates.

Purpose of the Study:

• To compare the efficacy of two distinct diagnostic algorithms in isolating Nontuberculous Mycobacteria (NTM).
• To assess the impact of laboratory procedure changes on NTM isolation rates and species composition.
• To investigate the potential underestimation of NTM infections due to diagnostic methods.

Main Methods:

• A retrospective analysis compared two diagnostic procedures for mycobacterial cultures.
• Procedure I utilized traditional *p*-nitrobenzoic acid (PNB) for preliminary NTM identification.
• Procedure II employed the MPT64 antigen detection method post-MGIT960 liquid culture for differentiating MTBC from NTM.

Main Results:

• Procedure II demonstrated a significantly higher NTM isolation rate (18.08%) compared to Procedure I (9.71%; P<0.001).
• The proportion of NTM among identified mycobacteria increased from 58.18% in 2019 to 72.93% in 2021, indicating improved species identification.
• No significant difference was observed in the consistency of species identification from multiple specimens between the two procedures.

Conclusions:

• NTM infections may be significantly underdiagnosed.
• The combination of MGIT960 culture and MPT64 antigen detection offers a timely and effective method for identifying NTM.
• This improved diagnostic strategy can enhance the accuracy and efficiency of NTM infection diagnosis.