Differentiating true coagulase-negative staphylococcal infection from contamination has an important impact on therapeutic implications. Time to positivity reflects bacterial density and may help in the interpretation of blood cultures. We retrospectively reviewed the records of 272 patients from June 2005 to January 2008 for clinical characteristics, microbiological data, and therapeutic outcome. Four groups were identified. The first three groups, as follows, included patients with one positive quantitative blood culture: the low-colony-count group (<10 CFU/ml), the moderate-colony-count group (30 to 100 CFU/ml), and the high-colony-count group (>100 CFU/ml). The control group included patients with two positive quantitative blood cultures and definite coagulase-negative staphylococcal bloodstream infection. The high-colony-count group had shorter time to positivity (<16 h) than did the low-colony-count group (P < 0.0001). The low-colony-count group had a significantly longer time to positivity, >20 h (P ‫؍‬ 0.001), than did the moderate-colony-count group. Even though antibiotics were not provided in 71% of cases and central venous catheter was retained in 83%, the low-colony-count group had a favorable outcome, suggesting that <10 CFU/ml represents contamination. The high-colony-count group, similar to the positive control group, required antibiotics in 81% of cases and central venous catheter removal in 51% (P ‫؍‬ 0.001). A time to positivity of <16 h reflects high-grade bacteremia with CFU of >100. Similar to the positive control group, these patients required an active therapeutic approach. A time to positivity of >20 h indicates possible contamination with a CFU of <10, and active therapy may not be required.

at their tertiary cancer center and compared the bacteria types and antimicrobial resistance in isolates from patients who had received antimicrobial agents as therapy or prophylaxis (breakthrough infections) with those from patients who had not received antimicrobial agents (nonbreakthrough bacteremia). RESULTS: Breakthrough bacteremia was more likely to be associated with MDR Escherichia coli (P ¼ .002), MDR Pseudomonas aeruginosa (P ¼ .02), and vancomycin-resistant enterococci (P ¼ .01). Multivariate analysis revealed that breakthrough bacteremia was associated with hematologic malignancies and neutropenia (odds ratios, 9.9 and 3.0, respectively). Fluoroquinolone use was associated significantly with the emergence of methicillin-resistant Staphylococcus aureus (P ¼ .04), MDR E. coli (P < .001), and MDR P. aeruginosa (P ¼ .05). A strong association was observed between fluoroquinolone use and breakthrough bacteremia in multivariate analysis (odds ratio, 22; P < .001). Patients who had received vancomycin were more likely to have vancomycin-resistant enterococci bloodstream isolates than patients who had not received antibacterial agents (P < .001). CONCLUSIONS: Breakthrough infections were more common in neutropenic patients and in patients who had hematologic malignancies. The isolation of MDR organisms was associated strongly with the use of fluoroquinolones. The current findings demonstrated the importance of using a comprehensive approach to the prevention of MDR bacterial infections, including the initiation of antibiotic stewardship programs. Cancer 2010;116:967-73.