Absence of non-tuberculous mycobacteria recovery in sputum of cystic fibrosis patients despite adequate decontamination: a possible role of specific antimicrobial therapy used in our centre

Objectives: Non-tuberculous mycobacteria (NTM) were pathogens of growing importance in non-paediatric cystic fibrosis (CF) patients. In our centre, the prevalence of NTM in these patients observed (0.5%) during the last decade was markedly inferior to those reported in the literature ranging from 6.5% to 24%. The aim of this study was to screen for NTM in adult patients in our centre with 3 different decontamination methods for mycobacterial cultures in order to determine whether the choice of the decontamination technique of samples may have an impact on their recovery in our centre. Methods: Between January and June 2009, consecutive sputum samples from adult patients with clinical suspicion of NTM infection (respiratory function degradation without other microbiologic explanation) were included in this study. 3 different decontamination protocols were used: N-acetyl-l-cysteine (NALC)-NaOH (DCT1), NALC-NaOH-oxalic acid 5% (DCT2) and DTT-Chlorhexidine 1% (DCT3). Decontaminated specimens were than cultured onto both solid Loewenstein-Jensen slants (LJ; BioRad) and liquid MGIT (BD) culture. A sample was considered NTM negative if no NTM isolate was recovered after a standard 42-day incubation protocol. Results: 36 sputum samples were collected from 26 adult patients during the study period. The median age of patients was 26 years. 88% of the patients received antimicrobial active against mycobacteria for more than 24 months before sputum collection (61% of the patients had fluoroquinolones and 88% had macrolides). No NTM was detected in the 36 specimens with none of the three decontamination techniques. Conclusions: Long-term use of macrolides and fluoroquinolones may be an explanation for the absence of recovery of NTM in these CF patients. Further studies in other CF centres prescribing similar antimicrobial treatment regimens are warranted to support this observation.