Coagulase-negative staphylococci (CoNS) are frequently isolated from blood cultures (BCs) of hospitalized patients.1 They have been associated with device infections, especially intravascular catheters2; however, predicting true infection with 1 positive BC of CoNS is difficult even in the presence of an intravascular device.3 Although physicians often consider 2 sets of BCs positive for CoNS as significant, the prediction of sepsis with 2 sets of positive BC was only 37% in 1 study.4
Blood cultures are frequently obtained in the emergency room setting as part of the workup for sepsis; in addition, they have been incorporated as quality indicators in guidelines.2,5 While the most effective intervention to reduce inappropriate antibiotic utilization is reducing contamination through compliance with aseptic procedures in obtaining the BC specimens, addressing the approach to positive BCs for CoNS by the treating physician may help reduce the inappropriate utilization of vancomycin. Multiple approaches have been described to differentiate true bacteremia from contamination of BCs6-12; however, little has been reported on the effect of the infectious diseases (ID) consultant on the utilization of vancomycin for positive BCs for CoNS.
At our facility, the use of vancomycin for more than 72 hours requires ID consultation. We wanted to evaluate the effect of ID consultation on the diagnosis of bacteremia in patients with 2 positive sets of BC for CoNS and antibiotic utilization, particularly vancomycin.
The study was performed in a 608-bed teaching hospital with 112,000 annual emergency department visits. We reviewed all BCs drawn on the patients in the emergency department of our hospital from July 2003 to July 2004. Patients admitted to the hospital with 2 sets of positive BC for CoNS (at least 1 bottle positive per set, each set representing a separate blood draw) were included for evaluation. All data were collected through retrospective record review. Data included symptoms on admission (shortness of breath, chills, fever, mental status changes), signs (respiratory rate, heart rate, blood pressure, and temperature), white blood cell count, presence of a prosthetic device, systemic inflammatory response syndrome (SIRS), use of antibiotics for the positive BC, and ID recommendation. Systemic inflammatory response syndrome was defined as the presence of 2 or more of the following: temperature greater than 38°C or less than 36°C, heart rate greater than 90 beats per minute, respiratory rate greater than 20 breaths per minute or Paco2 less than 32 mm Hg, and white blood cell count more than 12,000/μL or less than 4000/μL or with more than 10% immature neutrophils. The time to positivity of each BC and the type of organism in both BCs were also collected.
We abstracted information on whether ID consultation was obtained, the recommendation on the continuation, and discontinuation or initiating vancomycin for the positive BCs. We obtained an institutional review board exemption before starting the study (study fits under quality improvement). Data analysis was performed using SPSS, version 12.0 (SPSS Inc, Chicago, Ill). A 2-tailed Student t test was used for continuous variables, and a 2-sided Fisher exact test was used for categorical variables. A P < 0.05 for a 2-sided test was considered statistically significant.
Of 12,966 patients who had a BC drawn, 831 (6.4%) had at least 1 positive BC for CoNS. One hundred thirty patients (1.0%) had 2 positive BCs from which 113 records were available for review. The mean age was 63.4 years (SD, 18.2 years); 55 (48.7%) were males. The admitting diagnosis included fever (n = 7, 6.2%), sepsis (n = 11, 9.7%), pneumonia (n = 10, 8.8%), noninfectious respiratory or cardiac disease (n = 20, 17.7%), catheter related infection (n = 4, 3.5%), and other diagnoses (n = 61, 54%). Seventy (62%) met the criteria for SIRS on admission.
The mean time to positivity for the first and second BC were 3.49 days (SD, 3.0 days) and 3.55 days (SD, 3.0 days), respectively (not statistically significant). The same species was identified in both BCs in 103 patients (91%). Antibiotics were started on 67 patients (59%), of them 37 (55%) had prosthetic devices and 46 (65.7%) met the SIRS criteria. Vancomycin was initiated in 59 (88%) of them. Blood cultures grew the same organism in 61 (91%) and different organism in 6 patients (9%). The 2 BCs grew the same species and had the same antibiogram in 44 patients (98%) with prosthetic device compared with 59 (87%) in those with no prosthetic device (P = 0.04).
Infectious Diseases Consultation
Infectious diseases consultation was sought in 74 patients (65%). Fifty-two (70.3%) of consults were obtained within the first 48 hours of admission; the remaining 22 consultations were obtained on days 3 to 7 of admission. Of them, 63 patients had antibiotics started (vancomycin intravenously, n = 57; < 0.001). In the presence of prosthetic devices, ID continued antibiotics in 30 patients (88.2%), compared with 8 (19.8%) without a prosthetic device (P < 0.001). Finally, ID repeated BC in 20 patients (27%) compared with 1 (2.6%) of those with no ID evaluation (P = 0.001). Table 1 summarizes the use of antibiotics for 2 positive BCs and ID recommendations if consulted.
The Centers for Disease Control have issued 12 steps to prevent antimicrobial resistance among hospitalized adults.13 These include infection prevention, effective diagnosis and treatment, transmission prevention, and wise utilization of antibiotics. They also encourage consulting ID for serious infections and stress the importance of treating infection and not contamination or colonization. Moreover, the Centers for Disease Control has also issued recommendations to reduce the risk for vancomycin resistance.14 Vancomycin is discouraged in the treatment of a single BC positive for CoNS if contamination is likely. We evaluated the effect of the ID consultation on antibiotic utilization for 2 positive BCs for CoNS. Infectious diseases consultation was associated with a reduction by half of inappropriate utilization of vancomycin in the presence of a high prevalence of BC contamination. Interestingly, the presence of a prosthetic device was a strong predictor of antibiotic prescribing for 2 positive BCs and ID continuation of antibiotics. In our study, we included patients who had 2 positive BCs for CoNS; it is likely that the effect of the ID consultants is more pronounced if we extrapolate to those patients with 1 positive BC.
Antibiotic stewardship is essential to reducing inappropriate antimicrobial use and hence reducing resistance. Antibiotic restriction, before approval, and computer-assisted programs have been used to promote appropriate antibiotic utilization15,16; however, many hospitals lack any antibiotic management program.17 Optimizing the use of vancomycin through mandatory ID consultation after 72 hours of initiation is effective and may reduce unnecessary antibiotic utilization.
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