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Pseudo-outbreak of methicillin-resistant Staphylococcus aureus
P T Ender1, S J Durning, W K Woelk
1Division of Infectious Diseases, Wright-Patterson Medical Center, Wright-Patterson AFB, Ohio 45433-5529, USA.
Mayo Clinic Proceedings
|September 17, 1999
Summary
Laboratory misclassification led to a high rate of methicillin-resistant Staphylococcus aureus (MRSA) detection. Most MRSA cases were false positives, causing unnecessary vancomycin use and infection control measures.
Area of Science:
- Clinical Microbiology
- Infectious Diseases
- Diagnostic Accuracy
Background:
- High rates of methicillin-resistant Staphylococcus aureus (MRSA) can strain healthcare resources.
- Accurate laboratory identification of MRSA is crucial for effective treatment and infection control.
Purpose of the Study:
- To investigate if laboratory misclassification contributed to the observed high rate of MRSA.
- To assess the impact of potential misclassification on patient care and hospital protocols.
Main Methods:
- Comparison of automated Vitek system results with oxacillin agar screen and broth microdilution.
- Testing of discordant isolates for the presence of the mecA gene.
- Evaluation of S. aureus isolates over a 60-day period.
Main Results:
- 72% of isolates initially identified as MRSA by the Vitek system were oxacillin susceptible via agar screening.
- Discordant isolates were confirmed as oxacillin susceptible and mecA gene negative.
- Misclassification led to unnecessary vancomycin use and infection control measures.
Conclusions:
- Automated susceptibility testing for S. aureus requires periodic validation.
- Hospitals should implement confirmatory testing to prevent MRSA misclassification.
- Accurate MRSA identification is vital to avoid resource misallocation.