Quality Control and Infection Prevention
Core concepts
Quality control in microbiology differs from chemistry because the "analyte" is living. Understand internal QC (daily or per-lot checks of media, stains, antisera, and reagents), external QC (proficiency testing via CAP or API), and quality assurance (the broader program including audits and corrective action). Know the triggers for corrective action: failed QC, proficiency test failures, or trends on a Levey-Jennings chart.
For infection prevention, know standard precautions (applied to all patients regardless of diagnosis) versus transmission-based precautions (contact, droplet, airborne). Understand hand hygiene as the single most effective intervention, and the chain of infection as a framework. Know the significance of multidrug-resistant organisms (MRSA, VRE, CRE, C. difficile) and the laboratory's role in surveillance cultures and outbreak investigation (pulsed-field gel electrophoresis historically, now whole-genome sequencing).
Traps to expect
- Confusing standard vs transmission-based precautions - questions often describe a scenario and ask which applies.
- Assuming a single failed QC result invalidates all prior patient results; the response depends on the analyte and whether the failure is random or systematic.
- Overlooking that media QC requires both positive and negative controls with defined ATCC strains.
- Mixing up sterilization (destroys all microorganisms including spores) with disinfection (reduces but may not eliminate spores).
Worked example / rule of thumb
A blood culture bottle shows growth but the Gram stain QC on the same day fails. Rule of thumb: investigate the QC failure before reporting, and if the failure is systematic (e.g., reagent lot), review and possibly repeat affected patient results. Document corrective action - regulatory inspectors look for the documented loop, not just the fix.