Molecular assessment of mycobacterial burden in the treatment of nontuberculous mycobacterial disease

Introduction Nontuberculous pulmonary disease causes significant morbidity and mortality. Efforts to tackle infections are hampered by the lack of reliable biomarkers for diagnosis, assessment and prognostication. The aim of this study was to develop molecular assays capable of identifying and quantifying multiple nontuberculous mycobacterial (NTM) species and to examine their utility in following individual patients’ clinical courses. Methods DNA was extracted from 410 sputum samples obtained longitudinally from a cohort of 38 patients who were commencing treatment for either Mycobacterium abscessus or Mycobacterium avium complex or who were patients with bronchiectasis who had never had positive cultures for mycobacteria. NTM quantification was performed with quantitative PCR assays developed in-house. Results The molecular assays had high in vitro sensitivity and specificity for the detection and accurate quantification of NTM species. The assays successfully identified NTM DNA from human sputum samples (in vivo sensitivity: 0.86–0.87%; specificity: 0.62–0.95%; area under the curve: 0.74–0.92). A notable association between NTM copy number and treatment (Friedman ANOVA (df)=22.8 (3), p⩽0.01 for M. abscessus treatment group) was also demonstrated. Conclusion The quantitative PCR assays developed in this study provide affordable, real-time and rapid measurement of NTM burden, with significant implications for prompt management decisions.