Novel external quality assurance scheme for drug susceptibility testing of non-tuberculous mycobacteria: A multicentre pilot study

Objectives: Our aim was to conduct a multicentre study involving laboratories participating in the European TB Reference Laboratory Network aiming to develop a pilot external quality assessment (EQA) scheme for drug susceptibility testing (DST) of non-tuberculous mycobacteria (NTM). Methods: The study comprised a survey using a structured questionnaire followed by a pilot EQA round using identical panels of 10 Mycobacterium avium (MAV) and Mycobacterium abscessus (MAB) isolates. EQA results were received from 16 laboratories utilizing the broth microdilution method. Consensus modal MIC values were determined, and essential and categorical agreement rates were calculated. Results: Twenty-four out of 31 laboratories (77.4%) reported DST for NTM routinely. Essential agreement ranged from 78.8% (amikacin) to 96.2% (linezolid) for MAV and from 76.0% (amikacin) to 100% (doxycycline) for MAB. Categorical agreement ranged from 56.8% (moxifloxacin) to 100% (clarithromycin) for MAV and from 53.6% (linezolid) to 100% (doxycycline) for MAB. Conclusions: Our results show that interlaboratory reproducibility of DST for NTM is insufficient, highlighting the need for expanding EQA schemes. As EQAs for Mycobacterium tuberculosis complex have led to more reliable and reproducible DST, we propose to follow a similar approach for clinically relevant NTM.