Quantitative blood cultures in candidemia

The relationship between quantitative data on peripheral blood cultures and source of infection was studied in 172 episodes of candidemia that occurred in 169 patients. Clinically, the source of candidemia was an intravascular device in 67 episodes, an extravascular source in 73 episodes, and endocarditis in 2 patients; no source was identified for the other 30 episodes. Colony counts were determined in peripheral blood specimens on the first day of candidemia by the lysis-centrifugation system. High-grade and low-grade candidemia were defined as 25 colony-forming units or more per 10 ml and 10 colony-forming units or fewer per 10 ml of blood, respectively. Of 48 episodes of high-grade candidemia, 43 (90%) were associated with an infected intravascular device; therefore, the presence of high-grade candidemia should prompt the removal of intravascular devices. In contrast, 92 of the 112 episodes of low-grade candidemia (82%) had an extravascular or an unidentified source of candidemia. In patients with infections associated with an intravascular device, colony counts declined significantly within 72 hours after removal of the device in the absence of antifungal therapy; failure to decline suggests an alternative source of persistent infection. Quantitative data from peripheral blood cultures may help distinguish intravascular from extravascular sources of candidemia and aid in assessing the response to the removal of infected intravascular devices.     

Detection of Staphylococcus aureus in peripheral blood stem cell cultures after sterilization of standard blood cultures

We report central venous catheter (CVC)-associated Staphylococcus aureus bacteremia detected by apheresis product culture after sterilization of standard blood cultures. A 64-year-old man with non-Hodgkin's lymphoma underwent peripheral blood stem cell (PBSC) collection. Five days after placement of a CVC, inflammation was evident at the insertion site. The CVC was removed and cephalexin was begun. Discharge at the site contained neutrophils and gram-positive cocci in pairs and clusters. Cultures of the discharge, of blood drawn via the CVC, of the CVC tip and of the apheresis product collected that day grew methicillin-susceptible S. aureus (MSSA). Cephalexin was discontinued in favor of oxacillin. Three days after removal of the CVC, PBSC collections were resumed via a contralateral CVC. Three sets of standard blood cultures drawn the day the new CVC was placed and the following day were negative, yet apheresis product cultures from each of these days grew MSSA. PBSC collections were halted, the CVC was removed, and oxacillin was continued via a peripherally inserted central catheter. Transesophageal echocardiography after two weeks of therapy revealed thickened mitral leaflets and damage to the posterior leaflet. Transthoracic echocardiography 11 weeks preceding this study had demonstrated normal mitral valve anatomy and function. Oxacillin was continued for six weeks, after which PBSC collections were resumed. Pulsed-field gel electrophoresis of the MSSA isolates revealed a clonal pattern. Cultures of apheresis product may be more sensitive to the presence of bacteremia than standard blood cultures, and they should guide clinical decisions when the bacteria isolated are potential pathogens or suggest clinical infection.     

The prevention of contaminated blood cultures

Blood culture contamination represents a source of frustration for clinicians and microbiologists. Contaminated cultures lead to diagnostic uncertainty and are associated with increased health care costs due to unnecessary treatment and testing. Several strategies have been investigated to decrease contamination rates and numerous approaches to distinguish between clinically significant bacteremia and contamination have been explored. In this review, an overview of blood culture contamination is provided and the potential utility of a variety of approaches to improve both detection and prevention is discussed. Multidisciplinary efforts and multitargeted strategies are required to improve the quality and reliability of blood culture sampling.     

Development of subsequent bloodstream infection in patients with positive Hickman catheter blood cultures and negative peripheral blood cultures

There are limited data on the incidence of subsequent bloodstream infection (BSI) and the effect of systemic antibiotics in patients who had positive catheter-drawn blood cultures (CBC) and negative peripheral blood cultures (PBC). We retrospectively reviewed all paired blood cultures from patients with Hickman catheter in the hematology-oncology ward between January 1997 and December 2008. There were 112 episodes with positive CBC and negative PBC. Nine episodes (8.0%; 95% CI, 3.0-13.1%) led to subsequent BSI within 28 days. Subsequent BSI developed in 6 of 31 episodes (19%) where empiric antibiotics were inappropriate but in 3 of 81 episodes (4%) where empiric antibiotics were appropriate (P = 0.01). Subsequent candidemia (50%, 2 of 4) was more common than subsequent bacteremia (6%, 7 of 108) (P = 0.03). In conclusion, for patients with positive CBC and negative PBC, the overall incidence of subsequent BSI was 8.0%, and inappropriate empiric antibiotics was associated with subsequent BSI.     

Rapid identification of organisms from blood cultures

A rapid method is described for the identification of organisms directly from blood culture broths, using antisera to group specific antigens and various commercially available serological and biochemical reagents. The technique identified clinically significant organisms within 1 to 3 h of a positive signal in the BACTECTM blood culture system. The method is of value in providing more rapid diagnoses and treatment of patients, and could be applied to other blood culture systems.     

Gonococcal endocarditis with initially negative blood cultures

This case of gonococcal endocarditis in a young man highlights the recognized capacity of Neisseria gonorrhoeae to destroy an infected valve, and illustrates that emergency valve replacement in the presence of congestive heart failure may be life-saving. The utility of the echocardiogram and the reportedly low yield of positive blood cultures in this disease are represented.     

The right way to do blood cultures

Blood samples contaminated by skin-surface bacteria can increase hospital stays, cause the needless use of antibiotics, and cost thousands of dollars per incident. A few simple steps can reduce contamination and save patients and healthcare providers money, time, and heartache.     

The value of outpatient blood cultures in the emergency department

The value of adult outpatient blood cultures was assessed by a retrospective chart review of all patients for whom cultures were obtained in an emergency department. Eighty-six of 411 patients for whom cultures were obtained were not admitted. Five of these 86 patients were identified as being bacteremic by positive blood culture growth the next day, and three of the five had endocarditis. All endocarditis patients had identifiable risk factors for this disease. Although blood cultures cannot be recommended for most patients discharged from the emergency department with a febrile illness, they are helpful in detecting endocarditis and other bacteremic conditions before obvious signs develop.     

237例血培养阳性结果分析

目的：对血培养病原菌的种类分布和耐药情况进行回顾性分析，为临床用药提供依据。方法采用VersaTREK全自动血培养仪及配套血培养瓶连续监测培养细菌，阳性瓶及时转种。用MicroScan A/S-4微生物分析仪及配套试剂对分离菌进行鉴定和药敏试验。结果2460例血培养标本中共分离出237株病原菌，居前5位的病原菌依次为凝固酶阴性葡萄球菌、大肠埃希菌、肺炎克雷伯菌、金黄色葡萄球菌和肠球菌。临床分布以ICU、普外科及呼吸内科为主。药敏结果显示：革兰阴性杆菌对亚胺培南高度敏感，未发现耐万古霉素和利奈唑胺的革兰阳性球菌。结论及时了解血培养结果可以为临床抗菌治疗提供依据，对提高治愈率有重要的意义。     

Effect of antimicrobials on blood cultures in endocarditis

To study the effect of antimicrobials on bacterial growth in blood cultures, we used both simulated blood cultures and cultures obtained from rabbits with experimental endocarditis. Four strains of bacteria were incubated individually with six antimicrobials in nine blood culture media. Positivity rates varied with the ratio of the antimicrobial concentration to the MIC of the organism: 161 of 162 cultures (99%) were positive when the ratio was less than 1/10; 52 of 108 (48%) were positive when the ratio was between 1/10 and one; and none of 54 were positive when the ratio was greater than one. Endocarditis was produced in 28 rabbits with either E. coli, P. aeruginosa, S. aureus, or viridans streptococcus. Following a single dose of an antimicrobial, blood was taken for culture in eight media. Only for viridans streptococcus did recovery rates vary significantly in different media. Recovery rates for this organism in two supplemented peptone broths (78% and 89%) and in hypertonic supplemented peptone (78%) were each higher than in thioglycolate (22%), Columbia (22%), Bactec aerobic and anaerobic (11%), and trypticase soy broths (11%) (p less than 0.05 for each pair). Growth of bacteria in blood cultures containing antimicrobials depended on the ratio of the antimicrobial concentration to the MIC and, for viridans streptococcus, the blood culture medium.     

Clinical impact of blood cultures taken in the emergency department.

OBJECTIVES: (1) To establish the proportion of blood cultures that yield a positive microbiological culture. (2) To determine what proportion of blood cultures taken in the emergency department impact on patient management. (3) To develop guidelines for the appropriate ordering of blood cultures from patients in the emergency department (ED). METHODS: Retrospective review of all blood cultures taken in the ED of a metropolitan teaching hospital between 26 September 1995 and 30 June 1996. RESULTS: One thousand and sixty two blood cultures were taken from patients in the ED during the study period. Ninety two (9%) returned a positive microbiological culture. Of these, 52 (5%) were "true" positives and 18 (1.6%) resulted in changes in management. CONCLUSIONS: Blood cultures taken in the ED rarely yield positive cultures. Only 1.6% of blood cultures taken in the ED impact on management of patients. Simple strategies could reduce the number of blood cultures ordered with little prospect of patient compromise.     

Reevaluation of anaerobic blood cultures in a Veteran population

BACKGROUND: Studies suggest that the selective use of anaerobic blood cultures may represent a more cost-effective laboratory approach when anaerobic bacterial infection is suspected. METHODS: A 5-year retrospective study was done at a Veterans' Affairs hospital to determine the utility of routinely including anaerobic blood culture when sampling for bacteremia. RESULTS: A total of 22,075 anaerobic blood cultures were collected from our adult population. Significant anaerobic pathogens were isolated from only 0.14% of these blood cultures. An anaerobic infection could have been suspected in 92% of our patients. CONCLUSIONS: Significant anaerobic bloodstream infections occurred in only 0.14% of blood cultures. In addition, the majority of the patients identified with anaerobic bacteremia had clinical conditions that would have suggested a high likelihood of anaerobic bacteremia. These observations suggest that selective rather than routine use of anaerobic blood cultures may be appropriate in a veteran population.     

Utility of blood cultures in febrile children with UTI

The objective of the study was to define the prevalence of bacteremia in febrile children <18 years of age diagnosed to have acute urinary tract infection (UTI). Retrospective chart review of patients diagnosed to have a UTI in the emergency department (ED) of an urban, tertiary care children's hospital was conducted Seven hundred forty-four children were discharged or admitted from the ED with a diagnosis of UTI during the study period. Thirty-six (4.8%) patient records were unavailable for review; 343 met inclusion criteria. Two hundred forty-nine patients (72.8%) had a history of fever. Blood cultures were performed on 183 (53.4%) patients. Of febrile patients, 178 (71.5%) had a blood culture performed. Seventeen of 183 (9.3%) blood cultures were positive. All (17/178, 9.5%) positive blood cultures were obtained from febrile patients. Seven of the positive blood cultures were considered to be contaminated. The prevalence of true bacteremia in febrile patients was 5.6%. All 10 patients with a true pathogen recovered from the blood culture had the same organism in their urine culture. The prevalence of bacteremia in patients younger than 2 months was 22.7% and in patients between the ages of 2 months and 36 months, 3.0%. Patients with a positive blood culture were more likely to be younger, to have been hospitalized and to have had a longer duration of hospitalization. No difference was found between patients with a positive blood culture and those without in regards to the number of days of illness before presentation, time to defervescence and mean white blood cell count. Bacteremia in children with UTI is most common in very early infancy. Children with UTI between the ages of 2 months and 12 years appear to have a low risk of bacteremia. Children who are bacteremic are likely to have identical organisms with identical antimicrobial sensitivities in both the urine and blood culture.     

Bacterial blood cultures in children with sickle cell disease

Background

Children with sickle cell disease (SCD) are considered at risk for bacteremia, especially when they present to the emergency department (ED) with fever.

Objective

We aimed to determine the incidence of bacteremia in children with SCD presenting with or without fever to a pediatric ED.

Methods

A retrospective chart review of 692 pediatric ED visits of children with SCD during a 2-year period was conducted.

Results

Seven blood cultures (6 homozygous and 1 heterozygous) had bacterial growth (1.3%; 95% confidence interval, 0.5-2.1), 3 of which were among febrile children (1.7%; 95% confidence interval, 0-3.6). All identified microorganisms are part of the normal skin or oral flora and could represent contamination. None of the patients had growth of the Streptococcus pneumoniae species.

Conclusion

A very low rate of bacterial growth and no S pneumoniae were found. The absence of S pneumoniae in our cohort can be associated with the addition of the 7-valent pneumococcal conjugate vaccine.