Coagulase-negative staphylococci in multiple blood cultures: strain relatedness and determinants of same-strain bacteremia

Staphylococcus hemolyticus: The Most Common and Resistant Coagulase-Negative Staphylococcus Species Causing Bacteremia in North India

INTRODUCTION

Coagulase-negative Staphylococcus (CoNS) species are normal skin commensals but may also cause bacteremia. Therefore, isolating a CoNS species on blood culture often leads to a diagnostic dilemma about whether to consider the isolate as a true pathogen or not. This study was done to understand the distribution of various CoNS species in bloodstream infections, determine their antibiotic resistance patterns, and identify possible risk factors and patient outcomes in hospital settings.

MATERIALS AND METHODS

Inpatients with confirmed bacteremia defined as isolation of the same CoNS species with similar antibiograms from paired blood culture bottles, which were obtained from patients with at least clinical evidence of infection, were included. The isolates obtained were studied for CoNS species distribution and antibiotic resistance patterns, and the corresponding patients were assessed for possible risk factors and outcomes.

RESULTS

A total of 170 CoNS isolates obtained from 85 patients were analyzed. Staphylococcus haemolyticus (S. haemolyticus)(90, 52.9%) was the most common species isolated, and it was also the most resistant of all, followed by S. hominis (50, 29.4%), S. epidermidis (26, 15.3%), S. lentus (2,1.2%), and S. succinus (2,1.2%). S. haemolyticus and S. hominis were significantly more isolated from patients aged 18-60 years and >60 years, respectively. Methicillin-resistant (MR)-CoNS (68.8%) were significantly more resistant than methicillin-sensitive (MS)-CoNS (31.2%) to certain antibiotics, and none were resistant to vancomycin, linezolid, or teicoplanin. Mortality occurred in 17.6% of patients, which was most commonly associated with S. haemolyticus infection.

CONCLUSION

Age-specific predisposition of CoNS species, high rates of methicillin resistance, and mortality in CoNS bacteremia are highlights of this study. To our knowledge, we are the first to study the age-related association of CoNS species.

Outcomes of Children Who Present to the Emergency Department After Hematopoietic Cell Transplantation

OBJECTIVES

Our primary objective was to describe emergency department (ED) presentation, treatment, and outcomes for children after hematopoietic cell transplantation (HCT). Our secondary objective was to identify factors associated with serious infection in this population.

METHODS

This is a retrospective review of HCT patients who presented to our university children's hospital ED from January 1, 2011, to June 30, 2013. Emergency department presentation, treatment, and outcomes were described. Descriptive statistics were used to compare children with definite serious infection with those without serious infection. Multiple binary logistic regression was performed for risk factors associated with definite serious infection.

RESULTS

Fifty-four HCT patients (132 encounters) presented to our ED. Most were transplanted for a malignant (46%) or metabolic (36%) diagnosis and were recipients of bone marrow (51%) or umbilical cord blood (45%). Fever was the most common complaint (25%). Emergency department laboratory (64%) or imaging (58%) studies were frequently obtained. Admission was common (n = 70/132, 53%), with 79% (n = 55) of admissions to intensive care or bone marrow transplant units. Thirty-five encounters had definite serious infection, 5 had probable serious infection, and 92 had no serious infection. Fever (P < 0.001) and high-risk white blood cell (WBC) count of less than 5 or greater than 15 k/μL (P < 0.001) were associated with definite serious infection. Fever (odds ratio = 8.84, 95% confidence interval = 2.92-26.73) and high-risk WBC (odds ratio = 6.67, 95% confidence interval = 2.24-19.89) remained significantly associated with definite serious infection in our regression model.

CONCLUSIONS

Children presenting to the ED after HCT require extensive support and resources, with more than half requiring admission. Fever and high-risk WBC are associated with serious infection.

Clinical Behavior of Implant Infections Due to Staphylococcus Epidermidis

Surgical implants and other foreign material are increasingly used in modern medicine to restore or to improve the function of the human body. Infection of an implant is associated with considerable morbidity due to frequent hospitalizations, surgery and antimicrobial treatment. The underlying mechanism is the formation of a bacterial biofilm on the surface of the implanted body. The recognition and diagnosis of implant infections is essential for further therapy and, above all, the decision to remove and exchange the implant.

Methods

We compared the data of 60 patients with implant infections with those of 60 patients with transient bacteremia caused by Staphylococcus epidermidis. The pathogens isolated from blood were characterized with regard to antimicrobial susceptibility and formation of biofilms using a static microtiter plate model. Wild type skin isolates from non-hospitalized healthy volunteers served as control with regard to antimicrobial susceptibility and biofilm formation.

Results

Clinical signs and symptoms, underlying diseases and outcome were not different in either group. However, patients with implant infection had fever over a longer time (mean 12 days versus 3 days, respectively, p & 0.05) and more often positive blood cultures than patients with transient bacteremia (3.1 versus 1.2, p & 0.05). Thrombocytopenia was observed in patients with implant infections but not in patients with transient bacteremia (p & 0.05). Biofilms were formed in 86.4 % of the isolates in implant infection, in 88.8 % in transient bacteremia and in 76.9 % of the isolates from healthy volunteers (not significant). Multi-resistance to penicillin, oxacillin, erythromycin, clindamycin, ciprofloxacin and trimethoprim was more common in the hospital strains than in the wild type strains (75.6 % versus 48.7 %, p & 0.05).

Conclusions

The clinical features of implant infections are indistinguishable from those of transient bacteremia. Persisting fever and multiple blood culture yielding the growth of skin flora bacteria are strong indicators for infection of implanted material. Biofilm formation and antimicrobial multiresistance, as common in implant infection as in transient bacteremia, seem to be accessory factors in infections due to Staphylococcus epidermidis.

Is First-Line Vancomycin Still the Best Option to Treat Staphylococcus Health Care-Associated Meningitis?

BACKGROUND

Cerebrospinal fluid (CSF) penetration of vancomycin through the blood-brain barrier is poor but important inflammation improved it. Hence, vancomycin is recommended for the treatment of community meningitis. However, what about mild inflammatory health care-associated meningitis? The aim of this study was to evaluate the impact of vancomycin diffusion on CSF in Staphylococcus epidermidis health care-associated meningitis.

CASE DESCRIPTION

This was a retrospective study of all consecutive patients with S. epidermidis CSF shunt-associated infection, which was treated by continuous intravenous vancomycin after standard of care (60 mg/kg/d after a loading dose of 15 mg/kg). Patient outcome, CSF protein level, and vancomycin concentration in CSF and serum were assessed. We report 6 consecutives cases. Clinical and biologic manifestations were of mild intensity. Meningeal permeability was moderately altered with low CSF protein levels. Despite appropriate vancomycin dosage resulting in high serum concentrations, CSF remained below the S. epidermidis minimal inhibitory concentration.

CONCLUSIONS

We propose to reassess vancomycin use as first-line therapy when meningeal inflammation is mild-to-moderate in favor of antibiotics, which have a better CSF penetration.

Staphylococcus capitis isolated from prosthetic joint infections

Further knowledge about the clinical and microbiological characteristics of prosthetic joint infections (PJIs) caused by different coagulase-negative staphylococci (CoNS) may facilitate interpretation of microbiological findings and improve treatment algorithms. Staphylococcus capitis is a CoNS with documented potential for both human disease and nosocomial spread. As data on orthopaedic infections are scarce, our aim was to describe the clinical and microbiological characteristics of PJIs caused by S. capitis. This retrospective cohort study included three centres and 21 patients with significant growth of S. capitis during revision surgery for PJI between 2005 and 2014. Clinical data were extracted and further microbiological characterisation of the S. capitis isolates was performed. Multidrug-resistant (≥3 antibiotic groups) S. capitis was detected in 28.6 % of isolates, methicillin resistance in 38.1 % and fluoroquinolone resistance in 14.3 %; no isolates were rifampin-resistant. Heterogeneous glycopeptide-intermediate resistance was detected in 38.1 %. Biofilm-forming ability was common. All episodes were either early post-interventional or chronic, and there were no haematogenous infections. Ten patients experienced monomicrobial infections. Among patients available for evaluation, 86 % of chronic infections and 70 % of early post-interventional infections achieved clinical cure; 90 % of monomicrobial infections remained infection-free. Genetic fingerprinting with repetitive sequence-based polymerase chain reaction (rep-PCR; DiversiLab®) displayed clustering of isolates, suggesting that nosocomial spread might be present. Staphylococcus capitis has the potential to cause PJIs, with infection most likely being contracted during surgery or in the early postoperative period. As S. capitis might be an emerging nosocomial pathogen, surveillance of the prevalence of PJIs caused by S. capitis could be recommended.

Rapid Time to Positivity of Cerebrospinal Fluid Culture with Coagulase-Negative Staphylococcus Is More Likely to Reflect a True Infection Than Contamination

OBJECTIVE

Cerebrospinal fluid (CSF) culture is the gold standard for diagnosing postoperative central nervous system infection. The time to positivity (TTP) of an automated continuous blood culture system may indicate the original concentration of the organism. Coagulase-negative Staphylococcus (CoNS), the common organism recovered in CSF, poses difficulty in differentiating infection from contamination. This study investigated the TTP of CSF culture with CoNS and its relationship to clinical parameters and prognosis.

METHODS

Adult neurosurgical patients with CoNS who recovered via the use of CSF culture in BacT/ALERT Pediatric FAN blood culture bottles and were admitted from September 2013 to July 2015 were enrolled. The demographics, clinical and microbiological data, and treatment were reviewed, and the TTP of each culture was retrieved.

RESULTS

Thirty-nine adult patients with CoNS recovered from CSF culture were included. The TTP ranged from 7.68 to 57.36 hours. A univariate logistic regression analysis indicated patients with rapid TTP (<21.5 hours) compared with those with longer TTP were more likely to be female, show an effective response to antibiotic therapy within 7 days, have clean-contaminated surgical incisions, and show CSF leak. A multivariate logistic regression analysis indicated that being female, an effective antibiotic therapy within 7 days, and clean-contaminated surgical incisions were independent predictors of rapid TTP.

CONCLUSIONS

Targeted antibiotic therapy was more likely to be beneficial to patients with a rapid TTP within 7 days, which suggested that CoNS with a rapid TTP represents the pathogen of central nervous system infection rather than contamination in neurosurgical patients.

Dynamics of Hemodialysis Catheter Colonization by Coagulase-Negative Staphylococci

Objectives:

Catheter colonization is a necessary but poorly characterized step in the pathogenesis of catheter-related infections. Colonization dynamics of central venous hemodialysis catheters were studied with emphasis on coagulase-negative staphylococci (CoNS) and their population genetics, antibiotic resistance, and biofilm formation. The homogeneity of CoNS colony morphotypes was evaluated.

Design:

Prospective, longitudinal study during 1,158 catheter-days with microbiological analysis of skin swabs, weekly catheter blood and brush samples, and catheter tips.

Setting:

Hemodialysis unit of a university hospital.

Patients:

Twenty-six patients with 24 non-tunneled and 5 tunneled catheters.

Results:

Nineteen (65.5%) of the catheters became colonized, 17 by CoNS. CoNS colonization of the inner lumen was observed in 17.2% of the catheters and was first detectable after 3 weeks. Colonization of the outer surface occurred in 44.8% of the catheters within a minimum of 2 weeks. PFGE of 53 CoNS revealed 10 clones and 20 unique isolates. Isolates from clones were more frequent in catheter blood and brush cultures than were unique isolates (41% vs 15%), were resistant to more antibiotics (median, 7 vs 2), and tended to more often carry theicaAgene (64.1% vs 40%). Four (23.5%) of the catheters showed colonization with a mixture of CoNS based on PFGE. The time from catheter insertion to such mixed CoNS colonization was longer than that for colonization with one CoNS PFGE pattern only (42 vs 25 days).

Conclusions:

Colonization of hemodialysis catheters is dominated by multidrug-resistant,icaA-positive CoNS clones. Mixed CoNS colonization occurs, but is delayed, suggesting a process of sequential superinfection (Infect Control Hosp Epidemiol2005;26:567-574).

Determining the Clinical Significance of Coagulase-Negative Staphylococci Isolated From Blood Cultures

Background and Objective:

Coagulase-negative staphylococci are both an important cause of nosocomial bloodstream infections and the most common contaminants of blood cultures. Judging the clinical significance of coagulase-negative staphylococci is vital but often difficult and can have a profound impact on an institution's bloodstream infection rates. Our objective was to develop an algorithm to assist in determining the clinical significance of coagulase-negative staphylococci.

Design:

A single experienced reviewer examined the medical records of 960 consecutive patients with positive blood cultures in a tertiary-care referral teaching hospital. Four hundred five of the cultures contained coagulase-negative staphylococci. A determination of clinical significance was made and the performances of various published algorithms that contained readily available clinical and laboratory data were compared.

Results:

Eighty-nine (22%) of the episodes were considered significant, whereas 316 were contaminants. Patients with bacteremia were significantly more likely to be neutropenic and exhibit signs of sepsis syndrome. The algorithm with the best combined sensitivity (62%) and specificity (91%) for determining the clinical significance of coagulase-negative staphylococci was defined as at least two blood cultures positive for coagulase-negative staphylococci within 5 days, or one positive blood culture plus clinical evidence of infection, which includes abnormal white blood cell count and temperature or blood pressure.

Conclusion:

Use of this algorithm could potentially reduce misclassification of nosocomial bloodstream infections and inappropriate use of vancomycin for positive blood cultures likely to represent contamination (Infect Control Hosp Epidemiol2005;26:559-566).

Determining the Significance of Coagulase-Negative Staphylococci Identified in Cultures of Paired Blood Specimens from Neonates by Species Identification and Strain Clonality

Of 13 paired coagulase-negative staphylococci (CoNS) isolates recovered from cultures of paired blood specimens obtained simultaneously from peripheral sites from neonates with clinical sepsis, 12 were identical species with identical genotypes. Isolation of CoNS in cultures of 2 blood samples obtained simultaneously from separate sites in neonates usually represents true infection.

Understanding Bacterial Isolates in Blood Culture and Approaches Used to Define Bacteria as Contaminants: A Literature Review

BACKGROUND

Interpretation of blood culture isolates is challenging due to a lack of standard methodologies for identifying contaminants. This problem becomes more complex when the specimens are from sick young infants, as a wide range of bacteria can cause illness among this group.

METHODS

We used 43 key words to find articles published between 1970 and 2011 on blood culture isolates and possible contaminants in the PubMed database. Experts were also consulted to obtain other relevant articles. Selection of articles followed systematic methods considering opinions from more than 1 reviewer.

RESULTS

After reviewing the titles of 3869 articles extracted from the database, we found 307 relevant to our objective. Based on the abstracts, 42 articles were selected for the literature review. In addition, we included 7 more articles based on cross-references and expert advice. The most common methods for differentiating blood culture isolates were multiple blood cultures from the same subject, antibiograms and molecular testing. Streptococcus pneumoniae, Hemophilus influenzae, Neisseria meningitidis and group A and B streptococcus were always considered as pathogens, whereas Bacillus sp., Diphtheroids, Propionibacterium and Micrococcus were commonly regarded as contaminants. Coagulase-negative staphylococci were the most frequent isolates and usually reported as contaminants unless the patient had a specific condition, such as long-term hospitalization or use of invasive devices (catheters).

CONCLUSIONS

Inaccurate interpretation of blood culture may falsely guide treatment and also has long-term policy implications. The combination of clinical and microbiological knowledge, patient's clinical history and laboratory findings are essential for appropriate interpretation of blood culture.

Clinical, biological, and microbiological pattern associated with ventriculostomy-related infection: a retrospective longitudinal study

BACKGROUND

Our aim was to describe the pattern of ventriculostomy-related infection (VRI) development using a dynamic approach.

STUDY DESIGN

Retrospective longitudinal study.

METHODS

We analyzed the files of 449 neurosurgical patients who underwent placement of external ventricular drain (EVD). During the study period, CSF sampling was performed on a daily base setting. VRI was defined as a positive CSF culture resulting in antibiotic treatment. For VRI patients, we arbitrary defined day 0 (D0) as the day antibiotic treatment was started. In these patients, we compared dynamic changes in clinical and biological parameters at four pre-determined time points: (D-4, D-3, D-2, D-1) with those of D0. For all CSF-positive cultures, we compared CSF biochemical markers' evolution pattern between VRI patients and the others, considered as a control cohort.

RESULTS

Thirty-two suffered from VRI. Peripheral white blood cell count did not differ between D-4-D0. Median body temperature, CSF cell count, median Glasgow Coma Scale, CSF protein, and glucose concentrations were significantly different between D-4, D-3, D-2, and D0. At D0, 100 % of CSF samples yielded organisms in culture. The physician caring for the patient decided to treat VRI based upon positive CSF culture in only 28 % (9/32) of cases. In the control cohort, CSF markers' profile trends to normalize, while it worsens in the VRI patients.

CONCLUSIONS

We showed that clinical symptoms and biological abnormalities of VRI evolved over time. Our data suggest that VRI decision to treat relies upon a bundle of evidence, including dynamic changes in CSF laboratory exams combined with microbiological analysis.

From the Skin to the Brain: Pathophysiology of Colonization and Infection of External Ventricular Drain, a Prospective Observational Study

Ventriculostomy-related infection (VRI) is a serious complication of external ventricular drain (EVD) but its natural history is poorly studied. We prospectively tracked the bacteria pathways from skin towards ventricles to identify the infectious process resulting in ventriculostomy-related colonization (VRC), and VRI. We systematically sampled cerebrospinal fluid (CSF) on a daily basis and collected swabs from both the skin and stopcock every 3.0 days for microbiological analysis including in 101 neurosurgical patient. Risk factors for positive event defined as either VRC or VRI were recorded and related to our microbiological findings. A total of 1261 CSF samples, 473 skin swabs, and 450 stopcock swabs were collected. Skin site was more frequently colonized than stopcock (70 (60%) vs 34 (29%), p = 0.023), and earlier (14 ±1.4 vs 24 ±1.5 days, p<0.0001). Sixty-one (52%) and 32 (27%) skin and stopcock sites were colonized with commensal bacteria, 1 (1%) and 1 (1%) with pathogens, 8 (7%) and 1 (1%) with combined pathogens and commensal bacteria, respectively. Sixteen positive events were diagnosed; a cutaneous origin was identified in 69% of cases. The presence of a pathogen at skin site (6/16 vs 4/85, OR: 11.8, [2.5–56.8], p = 0.002) and CSF leakage (7/16 vs 6/85, OR 10 [2.4–41.2], p = 0.001)) were the two independent significant risk factors statistically linked to positive events occurrence. Our results suggest that VRC and VRI mainly results from an extra-luminal progression of pathogens initially colonizing the skin site where CSF leaks.

Compatibility of Pulsed-Field Gel Electrophoresis Findings and Clinical Criteria Commonly Used to Distinguish Between True Coagulase-Negative Staphylococcal Bacteremia and Contamination

Objectives.

To evaluate the specificity and sensitivity of the clinical criteria widely used to differentiate true coagulase-negative staphylococcal (CoNS) bacteremia from contamination, using pulsed-field gel electrophoresis (PFGE) as the reference test.

Design.

The study sample consisted of 79 CoNS isolates recovered from cultures of blood from 38 patients. Medical charts of the patients were reviewed for demographic and clinical information. The relatedness of CoNS strains recovered from 2 or more successive blood cultures was analyzed by PFGE. Patients from whom similar strains were recovered were assumed to have true bacteremia, whereas patients from whom different strains were recovered were considered to have contaminated blood cultures. The clinical criteria comprised Centers for Disease Control and Prevention (CDC) surveillance definitions for bloodstream infection (BSI), as well as an alternative criterion based on the presence of fever, the presence of leukocytosis, the absence of another recognized infection, and the recovery of CoNS from 2 or more successive blood cultures.

Results.

Nineteen (50%) of the 38 patients had bacteremia due to similar strains; the remaining patients had bacteremia due to different strains. Criterion 2a of the CDC definition for BSI had a sensitivity of 100% and a specificity of 31.6% for distinguishing between true bacteremia and contamination. CDC criterion 2b had a sensitivity of 78.9% and a specificity of 52.6%.

Conclusions.

Molecular typing correlated poorly with the clinical criteria for true bacteremia. In view of the limited applicability of clinical criteria, more studies are needed to improve them. Periodic cross-sectional studies based on PFGE findings might be useful to estimate local contamination rates in an institution, which in turn can be used to improve the accuracy of the clinical diagnosis of bacteremia.

Evaluation of quantitative antibiotic susceptibility testing by Vitek 2 as a routine method to predict strain relatedness of coagulase-negative staphylococci isolated from blood cultures

To test the hypothesis that the strain relatedness of coagulase-negative staphylococci (CoNS) recovered from blood cultures can be inferred from automated antibiotic susceptibility testing (AST) results generated by Vitek 2, concordant or discordant AST results were compared with pulsed-field gel electrophoresis (PFGE) typing results for 119 CoNS blood culture isolate pairs. Concordant AST results were highly predictive of the strain relatedness of CoNS isolates.

Community-acquired meningitis due to Staphylococcus capitis in the absence of neurologic trauma, surgery, or implants

Community-acquired meningitis due to coagulase-negative staphylococci in adults has been rarely reported and generally develops in patients with ventricular shunts or after neurosurgery or neurotrauma. Staphylococcus capitis is a rare cause of adult meningitis. We describe a patient with community-acquired meningitis due to S. capitis, in the absence of traditional risk factors, with atypical presentation.

Bacterial substitution of coagulase-negative staphylococci for streptococci on the oral mucosa after hematopoietic cell transplantation

PURPOSE

Coagulase-negative staphylococci (CoNS) are frequently isolated from blood cultures of hematopoietic cell transplantation (HCT) patients. Generally, the use of central venous catheters is recognized as a significant risk factor for CoNS infection, while the impact of CoNS infection from oral ulcerative mucositis, which occurs frequently in HCT, may be underestimated. Here, we examined the bacteria on the buccal mucosa after HCT.

METHODS

Sixty-one patients were examined for bacteria on the buccal mucosa routinely once a week from 1 week before to 3 weeks after allogeneic HCT. Subjects were divided into groups with short and long periods of antibiotic use, and differences in bacterial substitution were evaluated. The relationships between type of HCT (conventional HCT or RIST) and bacterial substitution were also evaluated.

RESULTS

The changes in detection frequencies of CoNS and α-streptococci from before to 3 weeks after HCT were significant (P < 0.05, χ (2) test): 14.5-53.3% and 92.7-53.1%, respectively. Significant bacterial substitution of CoNS for streptococci was observed in the long-term antibiotic use group (P < 0.05, χ (2) test), but also occurred in cases with short-term or no antibiotic use. No relationships between type of HCT (conventional HCT or RIST) were observed.

CONCLUSION

Bacterial substitution of CoNS for streptococci occurred frequently on the buccal mucosa after HCT. In addition to antibiotic use, environmental factors may be involved in bacterial substitution. It is important to consider the presence of oral mucositis in CoNS infection after HCT.

Influence of postmortem time on the outcome of blood cultures among cadaveric tissue donors

Tissue banks provide tissues of human cadaver donors for transplantation. The maximal time limit for tissue retrieval has been set at 24 h postmortem. This study aimed at evaluating the evidence for this limit from a microbiological point of view. The delay of growth in postmortem blood cultures, the identification of the species isolated and clinical/environmental factors were investigated among 100 potential tissue donors. No significant difference was found in the rate of donors with grown blood cultures within (25/65=38%) compared with after (24/65=37%) 24 h of death. Coagulase-negative staphylococci and gastro-intestinal microorganisms were isolated within and after 24 h of death. Two factors--antimicrobial therapy and "delay before body cooling"--were significantly inversely related with donors' blood culture results. From a microbiological point of view, there is no evidence for avoiding tissue retrieval among donors after 24 h of death.

[Phenotyping of bacteria isolated in blood cultures from critical patients]

Bloodstream infections are a serious complication among critical patients. The detection of microbial pathogens in blood cultures is an important diagnostic tool. This study aimed to isolate and characterize bacteria from the blood of patients admitted to the clinical intensive care unit of a teaching hospital, between April 2003 and April 2004. The bacteria isolated were identified by biochemical/enzymatic tests and detection of the antimicrobial susceptibility profile using the disk diffusion method. A total of 304 blood cultures from 195 patients were evaluated. Forty-nine (16.1%) of the blood cultures presented microbe development. The predominant species was Pseudomonas stutzeri (18.2%). Gram-positive cocci and enterobacteria showed greater resistance to ampicillin; vancomycin and linezolid were the most active agents for Gram-positive cocci and carbapenems for Gram-negative rods. Because of the impact of bloodstream infection within the hospital context, additional studies are needed in order to give backing for prevention and control measures.

Significance of coagulase-negative staphylococci isolated from a single blood culture from neonates in intensive care

BACKGROUND

Coagulase-negative staphylococci (CoNS) are the most common pathogens of late-onset bacteraemia in neonatal intensive care units (NICUs). Discriminating true infection from contamination is difficult.

METHODS

To evaluate the significance of a single blood culture yielding CoNS from only one blood culture obtained from NICU infants between July 1999 and November 2000, paired blood cultures were obtained simultaneously from two peripheral sites from infants hospitalised in two NICUs with clinically suspected late-onset sepsis, and a single blood culture was obtained peripherally from infants hospitalised in a third NICU. Demographic data, predisposing factors, clinical manifestations, laboratory data, management and outcome of infants with either paired or single blood cultures yielding CoNS were analysed and compared.

RESULTS

Both blood cultures yielded CoNS during 26 episodes in 24 infants. A single blood culture which grew CoNS from one blood culture was identified during 24 episodes in 23 infants. Except for prior use of an umbilical venous catheter, there was no significant difference between the infants with CoNS isolated from a paired or a single blood culture in terms of demographic characteristics, predisposing factors, clinical manifestations, laboratory findings, management and outcome.

CONCLUSION

There was no difference in the clinical features of CoNS infection between single and paired CoNS-positive blood cultures.

Updated review of blood culture contamination

Blood culture contamination represents an ongoing source of frustration for clinicians and microbiologists alike. Ambiguous culture results often lead to diagnostic uncertainty in clinical management and are associated with increased health care costs due to unnecessary treatment and testing. A variety of strategies have been investigated and employed to decrease contamination rates. In addition, numerous approaches to increase our ability to distinguish between clinically significant bacteremia and contamination have been explored. In recent years, there has been an increase in the application of computer-based tools to support infection control activities as well as provide clinical decision support related to the management of infectious diseases. Finally, new approaches for estimating bacteremia risk which have the potential to decrease unnecessary blood culture utilization have been developed and evaluated. In this review, we provide an overview of blood culture contamination and describe the potential utility of a variety of approaches to improve both detection and prevention. While it is clear that progress is being made, fundamental challenges remain.

Avoiding trouble down the line: the management and prevention of hemodialysis catheter-related infections

Over the last 2 decades, hemodialysis catheter use has increased. Annually, approximately 30% of patients using a central venous catheter (CVC) experience a septic or bacteremic episode and are subsequently at risk of its associated long-term complications and mortality. Because of the serious clinical and financial impact of hemodialysis catheter-related bacteremias (HCRIs), standardized, validated definitions based on the hemodialysis patient population are necessary in order to better diagnose, monitor, and report HCRI for patient quality assurance and research purposes. The pathophysiology of HCRI involves a complex interaction between a triad that consists of the host patient, the infecting microorganism, and the vehicle catheter. Although the microorganism contribution in the pathogenesis of HCRI is likely most important, certain patient and catheter-related characteristics may be more amenable to manipulation. The key to managing HCRI is on prophylaxis against the initial microorganism catheter adherence and subsequent biofilm development. General and specific prophylactic maneuvers directed at both an intravascular and extraluminal route of microorganism entry are discussed including antibiotic- and silver-impregnated catheters and dressings, subcutaneous access devices, and topical prophylaxis at the exit site. In addition to systemic antibiotic use, the 3 methods of HRCI treatment using catheter salvage, guidewire exchange, and concurrent antibiotic lock are compared. The outcome and complications of HCRI may be serious and highlight the importance of careful, continual infection surveillance. Although the use of a multidisciplinary hemodialysis infection control team is desirable, staffing education and physician feedback have been shown to improve adherence to infection control guidelines and reduce HCRI.

Phenotypic and genotypic characterization of coagulase-negative staphylococci isolated in blood cultures from patients with haematological malignancies

Coagulase-negative staphylococci are the predominant aetiological agents in bacteraemic patients hospitalized for haematological malignancies. The aim of this study was to determine whether differences exist in the prevalence of icaAB genes and in the phenotypic and/or genotypic pattern between blood isolates of coagulase-negative staphylococci, interpreted as representing true bacteraemia, and contaminant isolates from patients with haematological malignancies. Eighty-two isolates representing true bacteraemia and 47 contaminant isolates were found among 76 patients. The most prevalent species in both groups of patients was Staphylococcus epidermidis (n=103; 80%). Biochemical typing using the Phene Plate system and genotyping using pulsed-field gel electrophoresis showed a tendency towards a more homogeneous pattern among isolates causing true bacteraemia compared with contaminant isolates. Two major genotypic groups of S. epidermidis were found in both the true bacteraemia group and the contaminant group, with concordant pulsotypes found as well. These groups may comprise isolates carrying specific virulence factors, but the prevalence of the icaAB genes did not differ between the true bacteraemia group and the contaminant group. No significant difference was seen between the two study groups regarding clinical symptoms or complications, use of central venous catheter, and levels of absolute neutrophil count or C-reactive protein.

[Contamination of blood cultures drawn from central vein catheter and peripheral venipuncture. Prospective study of 75 pairs]

OBJECTIVE

To determine the frequency of contamination, the sensitivity, specificity, and predictive values of cultures done with blood drawn through a central venous catheter or peripheral venipuncture.

DESIGN

Prospective cohort study of critical ill medical surgical intensive care patients in whom samples for paired culture were drawn through a central venous catheter or peripheral venipuncture during a period of 8 months (from August 1st 2001 to Mars 31st 2002).

RESULTS

During the study period, 75-paired cultures were studied. Fifteen peripheral blood cultures (20%) and 27 central blood cultures (36%) were positive and 6 peripheral blood cultures (8%) and 15 central blood cultures (20%) were contaminated (P=0.034). The organism most commonly responsible for contamination was Coagulase Negative Staphylococcus (16% of central blood cultures and 6.7% of peripheral blood cultures). The frequency of contamination was of 42.9% for blood cultures drawn through a femoral central venous catheter, of 10% for jugular, and of 19% for subclavian central venous catheter (P=0.22). For catheter draws compared with peripheral venipuncture, sensitivity was 100 and 75%, specificity was 76.2 and 90.5%, positive predictive value was 44.4 and 60% and negative predictive value was 100 and 95%.

CONCLUSION

Cultures of blood drawn through a catheter are more sensible and less specific than those obtained from a peripheral venipuncture and the organism most commonly responsible for contamination of blood cultures is Coagulase Negative Staphylococcus.

Molecular, technological and safety characterization of Gram-positive catalase-positive cocci from slightly fermented sausages

The population of Gram-positive catalase-positive cocci from slightly fermented sausages was characterized at species and strain level by molecular techniques and some technological and hygienic aspects were also considered. Staphylococcus xylosus was the predominant species (80.8%) followed by Staphylococcus warneri (8.3%), Staphylococcus epidermidis (5.8%) Staphylococcus carnosus (4.6%), and Kocuria varians (0.4%). Proteolytic activity was observed in 23% of the isolates. The species with the highest percentage of proteolytic strains was S. warneri. Lipolytic activity was found in 45.8% of the isolates and S. xylosus was the species with the highest percentage of lipolytic isolates. Biogenic amine production was not widely distributed (only 14.6% of the isolates). Tyramine was the most intense amine produced, although by only 4.6% of the isolates. Phenylethylamine was more frequently detected (10.8% of isolates) but at lower levels. Some strains also produced putrescine (3.3%), cadaverine (2.9%), histamine (1.3%) and tryptamine (0.4%). All isolates were susceptible to linezolid and vancomicin and over 70% were resistant to penicillin G, ampicillin and sulphonamides. Most of the mecA+ strains (only 4.6% of isolates) also displayed resistance to multiple antibiotics. A reduced enterotoxigenic potential was found. Only 3.3% of isolates showed staphylococcal enterotoxins genes, all identified as entC gene. The combination of RAPD-PCR and plasmid profiling allowed the discrimination of 208 different profiles among the 240 Gram-positive catalase-positive cocci characterized, indicating a great genetic variability.

Routine antimicrobial susceptibility testing of coagulase-negative staphylococci isolated from blood cultures: is it necessary?

The clinical significance of discontinuing routine antibiotic susceptibility testing (AST) of coagulase-negative Staphylococcus (CNS) isolates from blood cultures was investigated. Prospectively, AST was requested primarily for patients with serious underlying illnesses. Antibiotic use did not change significantly when AST was not performed routinely. Laboratory cost savings were 75% if AST was not performed, but more specimens were submitted from these patients. Oxacillin resistance in coagulase-negative staphylococci from blood cultures has remained > 70% since implementation of this protocol, while annual vancomycin utilisation has shown only small, incremental increases. Therefore, it is suggested that routine AST of CNS isolates from blood culture is not essential.

Practical approach to catheter-related bloodstream infections in paediatrics

Catheter-related bloodstream infections (CRBIs) are a common problem in paediatrics. Sterile insertion and proper care of the catheter is likely more important than the type of catheter in determining the rate of CRBIs. The accuracy of the diagnosis of CRBIs can be improved by comparing the time to positivity or the concentration of organisms in blood drawn through the catheter with blood drawn from other sites, or by changing the catheter over a guidewire and culturing the removed catheter. When a CRBI is suspected, the catheter should be removed if it is no longer required, the child is hemodynamically unstable, there are metastatic foci of infection, the infecting organism is Candida or a mycobacterium, or there is a tunnel infection. The necessity for catheter removal is controversial if the infecting organism is Staphylococcus aureus or a Gram-negative organism. In most other situations, the catheter only needs to be removed if bacteremia persists despite appropriate antibiotic use.

Erroneous reporting of coagulase-negative Staphylococci as Kocuria spp. by the Vitek 2 system

Misidentification of coagulase-negative staphylococci (CoNS) may delay appropriate treatment. We investigated 20 clinical isolates identified as Kocuria spp. by the Vitek 2 system. All were identified as CoNS by 16S rRNA gene sequencing (18 Staphylococcus epidermidis, 1 Staphylococcus haemolyticus). Four Kocuria isolates were shown to be identical to CoNS from the same patient by pulsed-field gel electrophoresis. Isolates identified by Vitek 2 as Kocuria most likely represent misidentified CoNS, and if clinically indicated, should be investigated further by genomic methods.

[Retrospective study of bacteremia diagnosed in an emergency department: frequency, susceptibility of microorganisms, and impact on therapeutic management]

OBJECTIVE

The authors had for aim to determine the prevalence of bacteremia diagnosed in an emergency department (ED), the susceptibility of microorganisms to antibiotics, and the impact on therapeutic management.

DESIGN

A retrospective analysis was made on patient features, microbiological ecology, susceptibility to antibiotics, and modalities of antimicrobial therapy in the Georges Pompidou European hospital ED of Hôpital, between 1 November 2001 and 30 June 2002.

RESULTS

One thousand four hundred and thirty two blood cultures were obtained from 1069 patients. The rate of positive cultures was 12%, but only 8.7% (n = 125) were proved as true bacteremia. The most frequently identified organisms were: Enterobacteriaceae (n = 63, 39.4%) with a predominance of Escherichia coli (n = 48, 30%), and Streptococcus pneumoniae (n = 16, 10%). Forty two cases of pyelonephritis and 34 of prostatitis both due to E. coli were diagnosed. 76.5% of these were resistant to amoxicillin, 64.7% to amoxicillin-clavulanic acid, 11.8% to ciprofloxacin, and 44% to cotrimoxazole. No resistance to third generation cephalosporin was detected in E. coli isolates. Fourteen S. pneumoniae pneumonia cases were diagnosed. 57.1% of isolates presented with a decreased susceptibility to penicillin (CMI > 0.1 mg/l). Susceptibility to amoxicillin and cefotaxim was 85.7% and 92.9% respectively. Blood culture was the only exam available for bacterial diagnosis in 51.5% of true bacteremia. 1.6% of blood cultures from ED samples had an impact on therapeutic management.

CONCLUSIONS

Blood culture is a relevant exam for the diagnosis of infection in patients admitted to the ED.

Mucosa or skin as source of coagulase-negative staphylococcal bacteraemia?

Nosocomial bacteraemia is associated with significant morbidity, mortality, and cost worldwide, and is most commonly caused by coagulase-negative staphylococci (CONS). Establishing the source of CONS bacteraemia is therefore important in the prevention and management of this infection. CONS infections are presumed to originate at the cutaneous sites of central venous catheters (CVCs), a belief that has led to prevention strategies that focus almost exclusively on the skin. However, mucosal colonisation by CONS is well established, suggesting that mucosal sites might be an important source of CONS bacteraemia. We review the published material that evaluates the source(s) of CONS. We included only studies that used a strict definition of CONS bacteraemia, evaluated skin and other potential sources of CONS, and studied the molecular association between CONS blood isolates and their potential sources. Three published reports fulfilled our criteria. In cancer patients with CONS or CONS bacteraemia, most of the colonising strains that had a molecular match with the strain recovered from the blood of the same patient were mucosal isolates; by contrast, no association was seen between CONS blood and skin isolates. Furthermore, in several patient populations evidence was reported of mucosal colonisation by CONS and in several reports experimental and clinical mucosal translocation of CONS with subsequent bacteraemia was documented. Together these data indicate that mucosal sites are an important source of CONS bacteraemia. Clinical strategies for the treatment of patients with a positive blood culture for CONS, the widespread use of antimicrobial-coated CVCs, and maximum barrier protection for CVC insertion should be reassessed, and strategies to decrease mucosal colonisation by CONS should be developed.

Use of quantitative antibiogram analysis to determine the clonality of coagulase-negative Staphylococcus species from blood culture

Two phenotypic methods, quantitative antibiogram analysis and colony morphology, were compared to pulsed-field gel electrophoresis (PFGE) for distinguishing the clonality of coagulase-negative Staphylococcus (CNS) species. The results of these three methods were correlated with the patients' clinical findings for 23 episodes in which CNS species were isolated from two blood culture bottles within a 24-h period. Quantitative antibiogram and colony morphology at 24 h correlated with PFGE typing in 21 (91%) and 20 (87%) episodes, respectively. All episodes associated with CNS strains with identical PFGE patterns had quantitative antibiogram similarity coefficients < 10, whereas most episodes associated with strains with different PFGE patterns had quantitative antibiogram similarity coefficients >or= 17. The CNS isolate pairs were less likely to be associated with infection if the strains had different PFGE types or a quantitative antibiogram similarity coefficient >or= 17. Clinical microbiology laboratories should consider use of the quantitative antibiogram similarity coefficient to aid clinicians in distinguishing infection-associated CNS blood isolates from contaminants.

Coagulase-negative staphylococci: clinical, microbiological and molecular features to predict true bacteraemia

Coagulase-negative staphylococci (CNS) are frequently isolated from blood cultures, where they may be only a contaminant or the cause of bacteraemia. Determining whether an isolate of CNS represents a true CNS bacteraemia is difficult, and there is no single criterion with sufficient specificity. The aim of this study was to assess those clinical, microbiological, pathogenic and genotypic features that characterize true CNS bacteraemia. Twenty patients having two or more blood cultures positive for CNS and 20 patients with only one positive blood culture were studied. Significant bacteraemia was defined according to clinical and laboratory criteria. Incubation time for blood cultures to become positive, macroscopic appearance of colonies, species determination, biotype, susceptibility to antimicrobials, PFGE pattern and adherence capacity were all studied. Clinical bacteraemia was present in 16/20 patients with two or more positive blood cultures and in 2/20 patients with only one positive blood culture. A significant difference was seen in the median time to positivity between the 18 clinical bacteraemias and 22 contaminations (23.6 versus 29.2 h; P = 0.04, Wilcoxon). There was also a significant difference between the two groups in the median absorbance of the slime test (1.36 versus 0.58; P = 0.005). All significant bacteraemias with two or more positive blood cultures had the same species identified, the same antimicrobial susceptibility pattern and the same PFGE pattern. In two patients with true bacteraemia with only one positive blood culture, the incubation time for the culture to turn positive was <24 h and the slime production absorbance was >2.5. The most useful parameters for the diagnosis of true CNS bacteraemia for patients with two positive blood cultures were incubation time until positive, species identification, antimicrobial susceptibility pattern, slime production and PFGE pattern. For patients with only one blood culture positive for CNS, the useful parameters for prediction of true bacteraemia were incubation time until positive and slime production, both of which are simple, low-cost tests.

Do antimicrobial-impregnated central venous catheters prevent catheter-related bloodstream infection?

Controversy surrounds the role of central venous catheters (CVCs) impregnated with antimicrobial agents in the prevention of catheter-related bloodstream infection (CRBSI). We reviewed the current literature to evaluate the efficacy of antimicrobial-impregnated CVCs for preventing CRBSI. Eleven randomized studies published in article form were identified that included a control group that received nonimpregnated CVCs. We evaluated study methodologies, inclusion of key patient characteristics, use of clinically relevant end points, and molecular-relatedness studies. Review of these 11 trials revealed several methodological flaws, including inconsistent definitions of CRBSI, failure to account for confounding variables, suboptimal statistical and epidemiological methods, and rare use of clinically relevant end points. This review also failed to demonstrate any significant clinical benefit associated with the use of antimicrobial-impregnated CVCs for the purpose of reducing CRBSI or improving patient outcomes. More rigorous studies are required to support or refute the hypothesis that antimicrobial-impregnated CVCs reduce the rate of or prevent CRBSI.

Infection of a ventriculoatrial shunt with phenotypically variable Staphylococcus epidermidis masquerading as polymicrobial bacteremia due to various coagulase-negative Staphylococci and Kocuria varians

The diagnosis of bloodstream infection with coagulase-negative staphylococci is frequently based on the isolation of the same organism from more than one blood culture. Phenotypic variation is a common characteristic of pathogenic strains of Staphylococcus epidermidis which may affect species identification by the microbiology laboratory. We describe a patient with a new onset of nephritis and gram-positive bacteremia. Gram-positive cocci grew in multiple blood cultures and were identified by the Vitek 2 system as Kocuria varians, Staphylococcus hyicus, and S. epidermidis. Bacterial isolates grew on blood agar and Congo red agar plates as two distinct morphotypes and exhibited phenotypic variation. Neither morphotype could be identified by the API-Staph assay. Cellular fatty acid analysis identified one of the morphotypes as S. epidermidis but could not identify the other morphotype. All isolates were found to be identical by pulsed-field gel electrophoresis, and both colonial morphotypes were identified as S. epidermidis by 16S ribosomal gene sequencing. Phenotypic variation of S. epidermidis may affect identification to the species level by phenotype-based identification systems. Caution should be exercised when differentiating between true infection and contamination based on strain identification.

Five-test simple scheme for species-level identification of clinically significant coagulase-negative staphylococci

A working scheme developed in our laboratory for identification (by species group and species) of coagulase-negative staphylococci (CNS) was evaluated with 201 consecutive isolates and then validated by using the reference method of Kloos and Schleifer (W. E. Kloos and K. H. Schleifer, J. Clin. Microbiol. 1:82-88, 1975). This five-test simple scheme (referred to here as the simple scheme) combines the novobiocin susceptibility test with tests for urease, pyrrolidonyl arylamidase, ornithine decarboxylase, and aerobic acid from mannose. The addition of one or two tests within a particular species group could then positively identify the isolate. Two commercial systems, Staph-Zym (Rosco) and API-Staph (bioMérieux), along with results obtained by using Rosco diagnostic tablets (nongrowth tests), were also compared with the reference method. One isolate could not be identified even by the reference method. Of the remaining 200 strains, 191 (95.5%) strains were correctly identified with Staph-Zym and 171 strains (85.5%) were correctly identified with API-Staph. The most frequent clinical CNS species isolated were Staphylococcus epidermidis (50.5%), S. haemolyticus (18.5%), S. saprophyticus subsp. saprophyticus (16.0%), S. lugdunensis (6.0%), and S. warneri (2.5%). The simple scheme validated with the reference method has demonstrated an excellent correlation in the identification of the three most frequent species isolated: S. epidermidis, S. haemolyticus, and S. saprophyticus subsp. saprophyticus. With the simple scheme, identification of CNS was possible within 24 h after the enzymatic tests were used, whereas up to 72 h is necessary for the growth tests. This methodology would be very useful in any clinical microbiology laboratory for the presumptive identification of CNS species groups and species.

Staphylococcus aureus in a single positive blood culture: causes and outcome

Single positive culture was encountered in 61/235 patients (26%) with Staphylococcus aureus in blood culture over a 2-y period. It represented either true bacteremia (n = 52 cases; 85.2%) or contamination (n = 9; 14.8%). In comparison to cases with < or = 2 positive cultures, these patients did not have less severe disease or a lower incidence of complications.

Bloodstream infection in neutropenic cancer patients related to short-term nontunnelled catheters determined by quantitative blood cultures, differential time to positivity, and molecular epidemiological typing with pulsed-field gel electrophoresis

To determine the rate of catheter-related bloodstream infection (CRBSI) among cases of primary bloodstream infection (BSI) in febrile neutropenic cancer patients with short-term nontunnelled catheters, quantitative paired blood cultures (Isolator) from the central venous catheter (CVC) and peripheral vein were obtained between November 1999 and January 2001. Bactec blood culture bottles were obtained to determine the differential time to positivity (DTP). CRBSI was defined as a quantitative blood culture ratio of >5:1 (CVC versus peripheral) with proven identity of isolates from positive peripheral and CVC blood cultures as confirmed by pulsed-field gel electrophoresis. Forty-nine episodes of primary BSI were detected among 235 cancer patients with febrile neutropenia. Of these, 18 episodes (37%) were CRBSI and 31 (63%) were BSI with an unknown portal of entry. Coagulase-negative staphylococci were present in nine cases of CRBSI (50%). The identity of isolates from peripheral and CVC blood cultures was confirmed in all cases. Earlier positivity (>2 h) of CVC-drawn versus peripheral blood cultures was observed in 18 of 22 CRBSI-associated blood cultures (sensitivity, 82%; specificity, 88%; positive predictive value, 75%; negative predictive value, 92%). In summary, CRBSI accounted for 37% of cases of primary BSI in this population of neutropenic cancer patients. DTP compares favourably with quantitative blood cultures for the diagnosis of CRBSI and may be particularly useful for patients in whom catheter salvage is highly desirable.

Molecular analysis of coagulase-negative Staphylococcus isolates from blood cultures: prevalence of genotypic variation and polyclonal bacteremia

Fifty-seven coagulase-negative Staphylococcus isolates from 22 inpatients who had > or =2 blood cultures that were positive for Staphylococcus within 24 hours were analyzed to determine the frequency of polyclonal bacteremia. Patients were considered to have bacteremia (14 patients) or contamination of sample (8 patients) on the basis of clinical criteria. Nine colonies were randomly selected from each blood culture and genotyped by means of SmaI digestion/pulsed-field gel electrophoresis. Relatedness was determined by calculation of the Dice coefficient of banding-pattern similarity (S(AB)). Analysis of bacteremic isolates demonstrated the presence of a single species in 35 of 41 blood cultures, 1 related variant in 5 blood cultures (87%-92% S(AB)), and an unrelated strain in 1 blood culture (79% S(AB)). Analysis of contaminated samples demonstrated the presence of a single strain in 10 of 16 blood cultures and 1-3 variants (28%-97% S(AB)) in the remainder. Genotype diversity was significantly more common in the contaminated samples (P=.036). Almost all coagulase-negative Staphylococcus bacteremias were monoclonal.

Molecular typing of coagulase-negative staphylococci from blood cultures does not correlate with clinical criteria for true bacteremia

PURPOSE

Determining whether a blood culture that contains coagulase-negative staphylococci represents bacteremia or contamination is a clinical dilemma. We compared molecular-typing results of coagulase-negative staphylococcal blood culture isolates with clinical criteria for true bacteremia.

SUBJECTS AND METHODS

Pulsed-field gel electrophoresis and arbitrary primed polymerase chain reaction (PCR) were used to determine whether patients with two or more blood cultures with coagulase-negative staphylococcal isolates had the same strain of organism in each culture (same strain bacteremia). We evaluated three different clinical criteria for bacteremia: whether the patient received more than 4 days of antibiotics, whether there was an explicit note in the medical chart in which the physician diagnosed a true bacteremia, and the Centers for Disease Control surveillance criteria for primary bloodstream infection. Agreement between same-strain bacteremia and each definition was examined, based on the assumption that most true infections should be the result of a single strain.

RESULTS

The study sample consisted of 42 patients and 106 isolates. Nineteen of the 42 bacteremias (45%) were the same strain. Classification of bacteremias as same-strain correlated poorly with all three clinical assessments (range of percent agreement, 50% to 57%; range of kappa statistic, 0.01 to 0.15). There were both false-positive and false-negative errors. Patients with three or more positive blood cultures were more likely to have same-strain bacteremia than those with only two positive cultures [11 of 15 (73%) vs 8 of 27 (30%), P = 0.006]. Pulsed-field gel electrophoresis was more discriminating than arbitrary primed PCR (percent agreement, 83%; kappa, 0.67).

CONCLUSION

Molecular typing correlated poorly with clinical criteria for true bacteremia, suggesting either that true bacteremias are frequently the result of multiple strains or that the commonly used clinical criteria are not accurate for distinguishing contamination from true bacteremia. Vancomycin treatment of clinically defined coagulase-negative staphylococcal bacteremia may frequently be unnecessary.