A German external quality survey of diagnostic microbiology of respiratory tract infections in patients with cystic fibrosis.

Background: The goal of this pilot study was to design an external quality assessment (EQA) scheme for German cystic fibrosis (CF) clinical microbiology laboratories. Therefore, a multicentre study of 18 German CF laboratories was performed to evaluate their proficiency in analyzing CF respiratory secretions.

Methods: Simulated clinical specimens containing a set of four frequent CF pathogens, namely two Pseudomonas aeruginosa strains differing in morphotype (mucoid versus non-mucoid) and resistotype, one Staphylococcus aureus strain and one Burkholderia multivorans strain, were distributed to each laboratory. Isolation, identification and antimicrobial susceptibility testing (AST) of any bacterial pathogen present and completion of a questionnaire about applied microbiological protocols were requested.

Results: Three of four strains were isolated and identified correctly by almost all laboratories. B. multivorans was once misidentified as Burkholderia cenocepacia. Fourteen laboratories failed to detect the second multidrug resistant P. aeruginosa isolate. AST errors occurred most often for P. aeruginosa 2 followed by B. multivorans, P. aeruginosa 1 and S. aureus. Evaluation of the questionnaires revealed major differences in cultivation and identification techniques applied by the participating laboratories.

Conclusions: A periodical EQA programme for German CF laboratories and standardized microbiological procedures seem to be necessary to advance diagnostic microbiology employed on CF respiratory tract specimens and may help to improve anti-infective treatment and infection control practices for CF patients.