Two blood culture sets were collected from a febrile adult. Set 1 grows coagulase-negative staphylococci in both aerobic and anaerobic bottles after 48 hours. Set 2 remains sterile after 5 days. The patient has no intravascular device. What is the correct interpretation?
- A Definite coagulase-negative staphylococcal endocarditis requiring rifampicin and gentamicin
- B Healthcare-associated bacteraemia mandating vancomycin
- C Most likely skin contamination, since growth was confined to one set and appeared late ✓
- D Laboratory cross-contamination during processing
Correct answer: C. Most likely skin contamination, since growth was confined to one set and appeared late
Explanation
Coagulase-negative staphylococci are the commonest blood culture contaminants. Contamination is suggested by growth in only one set, detection after more than 2 days of incubation, and absence of an indwelling device or immunosuppression. True CoNS bacteraemia typically grows in two or more sets within about 24 hours, especially with a catheter present. Vancomycin for a single contaminated set promotes resistance. Cross-contamination cannot be inferred from these findings alone.
Reference: Koneman's Color Atlas and Textbook of Diagnostic Microbiology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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