Less Is More: When to Repeat Antimicrobial Susceptibility Testing

Area of Science:

• Clinical Microbiology
• Infectious Diseases
• Antimicrobial Resistance

Background:

• Antimicrobial susceptibility patterns can change over time within the same patient.
• Monitoring these changes is crucial for effective treatment and infection control.
• The frequency and predictability of resistance development require further investigation.

Purpose of the Study:

• To investigate the frequency of changes in antimicrobial susceptibility patterns for common bacterial pathogens.
• To evaluate the risk of developing resistance over different follow-up periods.
• To assess the feasibility of omitting routine follow-up antimicrobial susceptibility testing.

Main Methods:

• Retrospective analysis of 18,501 antimicrobial susceptibility tests (AST) from January 2014 to December 2021.
• Focus on Escherichia coli, Klebsiella pneumoniae, Enterobacter spp., Pseudomonas aeruginosa, and Staphylococcus aureus.
• Utilized Vitek 2 system, determining essential and categorical agreement, and introducing new metrics for resistance changes.

Main Results:

• Staphylococcus aureus showed a <10% risk of resistance within 30 days.
• Enterobacterales exhibited approximately 10% risk of resistance within 7 days.
• Pseudomonas aeruginosa demonstrated a higher risk of resistance with longer follow-up periods; specific drug-bug combinations (e.g., E. coli/amoxicillin-clavulanic acid) were more prone to resistance.

Conclusions:

• A follow-up AST risk below 10% suggests omitting repeat testing within 7 days may be feasible for certain bacteria.
• This approach could lead to significant cost, time, and laboratory waste savings.
• Further research is needed to balance economic benefits against the risk of suboptimal antibiotic treatment.