A blood culture set consisting of one aerobic and one anaerobic bottle is collected from a febrile patient. The aerobic bottle turns positive at 14 hours with gram-positive cocci in clusters. The lab reports it as coagulase-negative Staphylococcus (CoNS). Under which circumstances should a single positive blood culture for CoNS be considered clinically significant?
- A When ≥2 of 2-3 blood culture sets drawn from different sites grow identical CoNS species, especially in patients with prosthetic devices, intravascular catheters, or immunocompromised states ✓
- B A single positive blood culture for CoNS is always clinically significant regardless of clinical context
- C CoNS in blood culture always indicates skin contamination and should be disregarded
- D Clinical significance requires CoNS to be present only in anaerobic bottles
Correct answer: A. When ≥2 of 2-3 blood culture sets drawn from different sites grow identical CoNS species, especially in patients with prosthetic devices, intravascular catheters, or immunocompromised states
Explanation
CoNS (S. epidermidis, S. haemolyticus, etc.) are the most common blood culture contaminants (representing ~20% of contaminants) but are genuine pathogens in patients with prosthetic valves, intracardiac devices, CNS shunts, central venous catheters, or immunosuppression. Clinical significance requires identical CoNS species/antibiogram in ≥2 of 2–3 independent blood culture sets collected from different venipuncture sites; this markedly reduces the probability of contamination. A single positive CoNS in one bottle is most likely a contaminant.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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