Clonal diversity in episodes with multiple coagulase-negative Staphylococcus bloodstream isolates suggesting frequent contamination.

BACKGROUND

Coagulase-negative Staphylococci (CoNS) are frequently recovered from blood cultures, which may indicate contamination or true bacteremia.

PATIENTS AND METHODS

CoNS isolates recovered from patients with episodes of two or more blood cultures positive for CoNS within 24 h were typed by both pulsed-field gel electrophoresis (PFGE) and speciation.

RESULTS

PFGE typing of 94 CoNS isolates recovered from episodes with two or more positive blood cultures for CoNS within 24 h discriminated 35 strain clusters. The CoNS isolates were unrelated in 15 (39%) of 38 episodes, suggesting contamination. Sensitivity and specificity of CoNS speciation compared to PFGE was 96% and 67%, respectively. Clonal and species diversity differed between hospital areas.

CONCLUSION

Contamination may frequently be present even in the setting of the recovery of CoNS from two or more blood culture sets within 24 h. Speciation of CoNS bloodstream isolates is rapid and may improve patient care as well as reduce unnecessary antibiotic use.