The quality of antimicrobial susceptibility test discs and implications for clinical outcomes

Disc diffusion remains the main technique for evaluating antibiotic activity in clinical microbiology laboratories. However, the assay protocol endorsed by the FDA, DIN, and WHO is invalid. Despite decades of research and practice in this field, the quantitative quality of manufactured discs is largely unknown, potentially leading to adverse clinical outcomes. The usual standards expected for new medical devices in terms of quality control, QA, and evidence-based assessment of outcomes are almost completely lacking. Recent data indicate that a large proportion of discs do not meet the specifications, and that disc diffusion is a poor predictor of clinical outcomes. In addition, lack of harmonisation between EUCAST and CLSI, despite many years of effort, strongly suggests that there are serious flaws in these systems. This area lacks scientific rigour, which may have also contributed to adverse clinical outcomes and the emergence of antimicrobial resistance.