Pediatric Blood Cultures

Immune phenotyping in a pediatric multicenter transplant study: Suitability of a preformulated dry-antibody panel system

Flow-cytometric immune phenotyping is influenced by cryopreservation and inter-laboratory variability limiting comparability in multicenter studies. We assessed a system of optimized, pre-mixed dry-antibody panel tubes requiring small amounts of whole blood for validity, reliability and challenges in a Canadian multicenter study (POSITIVE) with long-distance sample shipping, using standardized protocols. Thirty-seven children awaiting solid-organ transplant were enrolled for parallel immune-phenotyping with both validated, optimized in-house panels and the dry-antibody system. Samples were collected before, 3 and 12 months post-transplant. Quality-assurance measures and congruence of phenotypes were compared using Bland-Altman comparisons, linear regression and group comparisons. Samples showed excellent lymphocyte viability (mean 94.8 %) and recovery when processed within 30 h. Comparing staining methods, significant correlations (Spearman correlation coefficient >0.6, p < 0.05), mean difference <5 % and variation 2SD <25 % were found for natural-killer, T and B cells, including many immunologically important cell subsets (CD8+, naïve, memory CD4+ T; switched-memory, transitional B). Some subgroups (plasmablasts, CD1d+CD5hi B cells) showed weak correlations, limiting interpretation reliability. The dry-antibody system provides a reliable method for standardized analysis of many immune phenotypes after long-distance shipping when processed within 30 h, rendering the system attractive for pediatric studies due to small blood amounts required and highly standardized processing and analysis.

Clinical usefulness of anaerobic blood culture in pediatric patients with bacteremia

OBJECTIVES

The purpose of this study is to evaluate the usefulness of anaerobic blood culture in pediatric patients by comparing the detection rate and distribution of bacteria between aerobic and anaerobic blood culture bottles.

METHODS

A retrospective analysis was conducted on 11,664 blood cultures obtained from children under the age of 14 between January 2013 and June 2020. The positive rate of total, aerobic, and anaerobic blood culture, as well as the species distribution of each blood culture bottle, were investigated.

RESULTS

The positive rate of blood culture was 2.4 % (N = 281). Among them, 67 (23.8 %), 85 (30.3 %) and 129 (45.9 %) organisms were grown in only aerobic, only anaerobic, and both blood culture bottles, respectively. Gram-positive cocci were cultured on both, only aerobic, and only anaerobic blood culture bottles in proportions of 46.4 %, 23.4 %, and 30.2 %, respectively. Gram-negative bacilli were cultured on both, only aerobic, and only anaerobic blood culture bottles in proportions of 58.5 %, 12,3 %, and 29.2 %, respectively. Gram-positive bacilli grew best in aerobic bottle only. There were seven strains of obligate anaerobes.

CONCLUSION

Because many facultative anaerobic bacteria are recognized primarily from anaerobic blood culture bottles, combining aerobic and anaerobic blood culture bottles might be beneficial in pediatric patients with suspected blood stream infection.

Outcomes of Care-bundle Implementation for Children With Cancer and Suspected Bloodstream Infection in a Pediatric Oncology Unit in a Resource-limited Setting

Bloodstream infections (BSIs) are a major cause of mortality among pediatric oncology patients in resource-limited settings. Effective, innovative strategies are needed to improve care and survival. In a pediatric oncology unit in Mexico, we retrospectively analyzed the risk factors for mortality related to BSI and the results of using a care-bundle intervention. The care-bundle consisted of a swift clinical evaluation, initial fluid-resuscitation support, obtaining blood cultures, and administration of effective empirical antibiotic therapy for suspected BSI. The outcomes of patients who received the care-bundle during a 12-month period were compared with those of patients treated with standard care during the 12 months preceding its implementation. The primary outcomes were BSI diagnosis, choice of antibiotics, and mortality. Of the 261 suspected BSIs treated with standard care, 33 (12.6%) infections were confirmed, and of the 308 treated with the care-bundle, 67 (21.7%) BSIs were confirmed. Thus, after implementation of the care-bundle, significantly more BSIs were diagnosed ( P =0.004), and BSI-related mortality was significantly reduced by 22.2% ( P = 0.035). Surgical resection and mechanical ventilation support were independently associated with BSI-related mortality, and receiving effective initial empirical antibiotic therapy was protective against mortality (odds ratio, 0.013; 95% CI: 0.002-0.105; P =0.001), which comprising cefepime plus amikacin or meropenem in 44 (80.0%) of the cases alive. Consistent use of a care-bundle with initial fluid resuscitation, obtaining a blood culture, and administering effective antibiotics to children with cancer and suspected BSI can decrease mortality.

"Rationalization of Empiric Antibiotic Therapy" - A Move Towards Preventing Emergence of Resistant Infections

Antimicrobial resistance is a key factor leading to emerging/ re-emerging infections. Rational antimicrobial therapy or antimicrobial stewardship is one of the important interventions to prevent emergence of resistance. Choosing correct empiric therapy is crucial not only to prevent antimicrobial resistance but also to achieve good treatment outcomes. Antimicrobial therapy can be broadly classified as empiric, definitive/ targeted and preventive. It is in choice of empiric therapy that the largest margin of error exists. Paradoxically, empiric therapy is the most commonly employed therapy since microbiologic results are either not available at initiation of treatment or cannot be sent due to logistic reasons or are negative. In the Indian setting, where penetration of microbiologic diagnostic methods in small cities, towns and rural areas is still fairly low, therapy is largely empiric. Choice of empiric therapy is governed by various factors including likely pathogens, antimicrobial resistance, degree of sickness, site of infection and host co-morbidities. These principles can be applied to any clinical syndrome whether it is fever without focus, infections of the respiratory tract, gastrointestinal tract, abdomen, central nervous system, bone and joint, skin and soft tissue, urinary tract as well as neonatal sepsis and healthcare associated infections. Adherence to published guidelines for syndromic management such as that by the Indian Academy of Pediatrics and Indian Council of Medical Research is strongly recommended. One can tailor these guidelines and suggestions made in this article to an individual setting.

True Pathogen or Contamination: Validation of Blood Cultures for the Diagnosis of Nosocomial Infections in a Developing Country

BACKGROUND

Blood culture results are frequently used to guide antibiotic decision-making, but culture contaminants need to be distinguished from true pathogens.

AIMS

To assess the contamination rate of blood cultures and validate a method to distinguish between true bacteraemia and contamination.

METHODS

We analysed blood culture results from children who were admitted to the paediatric ICU and paediatric wards at the Sardjito Hospital, Yogyakarta, Indonesia between December 2010 and February 2013. For each positive culture result, the type of isolated organism, time to positivity, and the number of positive culture sites were considered to classify the isolate as representing a true bacteraemia or contaminant.

RESULTS

There were 1293 cultures obtained from blood and 308 (23.8%) were positive for bacterial growth. Fifty-three (4.1%) of the total cultures drawn fulfilled criteria for contaminants. The most common blood culture contaminants were coagulase-negative staphylococci.

CONCLUSION

Using standardized criteria, it is possible to implement a working method to identify true nosocomial infection from blood culture contaminant, and thus limit the effect of contaminated blood culture on irrational antibiotic use.

Bloodstream infections during the onset of necrotizing enterocolitis and their relation with the pro-inflammatory response, gut wall integrity and severity of disease in NEC

INTRODUCTION

Bacterial involvement is believed to play a pivotal role in the development and disease outcome of NEC. However, whether a bloodstream infection (BSI) predisposes to NEC (e.g. by activating the pro-inflammatory response) or result from the loss of gut wall integrity during NEC development is a longstanding question.

OBJECTIVE

We hypothesize that the occurrence of a BSI plays a complementary role in the pathogenesis of NEC. The first aim of the study was to correlate the occurrence of a BSI during the early phase of NEC with intestinal fatty acid-binding protein (I-FABP) levels, as a marker for loss of gut wall integrity owing to mucosal damage, and Interleukin (IL)-8 levels, as a biomarker for the pro-inflammatory cascade in NEC. The second aim of the study was to investigate the relation between the occurrence of a BSI and disease outcome.

MATERIAL AND METHODS

We combined data from prospective trials from two large academic pediatric surgical centers. Thirty-eight neonates with NEC, 5 neonates with bacterial sepsis, and 14 controls were included.

RESULTS

BSIs occurred in 10/38 (26%) neonates at NEC onset. No association between the occurrence of BSIs and I-FABP levels in plasma (cohort 1: median 11ng/mL (range 0.8-298), cohort 2: median 6.8ng/mL (range 1.3-15)) was found in NEC patients (cohort 1: p=0.41; cohort 2: p=0.90). In addition, the occurrence of BSIs did not correlate with IL-8 (median 1562pg/mL (range 150-7,500); p=0.99). While the occurrence of a BSI was not correlated with Bell's stage (p=0.85), mortality was higher in patients with a BSI (p=0.005).

CONCLUSION

The low incidence of BSIs and the absent association of both the markers for loss of gut wall integrity and the pro-inflammatory response during the early phase of NEC, support the hypothesis that the presence of a BSI does not precede NEC.

Epidemiological Evaluation of Blood Culture Patterns among Neonates Receiving Vancomycin

The objective of this study was to assess the frequency of blood culture (BC) collection among neonates who received vancomycin. Demographic, clinical, microbiologic, and pharmacy data were collected for 1275 neonates (postnatal age 0-27 days) who received vancomycin at an Intermountain Healthcare facility between 1/2006 and 9/2011. Neonates treated with vancomycin had a BC collected 94 % (n = 1198) of the time, of which 37 % (n = 448) grew one or more bacterial organisms (BC positive). Of these, 1 % (n = 5) grew methicillin-resistant Staphylococcus aureus (MRSA), 71 % (n = 320) grew coagulase-negative Staphylococci (CoNS), 9 % (n = 40) grew methicillin-sensitive Staphylococcus aureus (MSSA), and 22 % (n = 97) grew other bacterial species (total exceeds 100 % due to co-detection). In patients with negative BC or no BC, vancomycin therapy was extended beyond 72 h 52 % of the time. The median duration of vancomycin therapy for patients with a negative BC was 4 (IQR: 2-10) days. BCs were frequently obtained among neonates who received vancomycin. Vancomycin therapy beyond the conventional 'empiric' treatment window of 48-72 h was common without isolation of resistant gram-positive bacteria.

Identifying and classifying bloodstream infections among hemodialysis patients

Bloodstream infections (BSIs) are a prominent clinical problem in patients undergoing hemodialysis. These infections appear to be more common among patients who have a central line as their dialysis access and can be associated with substantial morbidity and mortality. Accurately diagnosing BSIs clearly influences patient management, but is also an important part of an infection prevention program; particularly as facility BSI rates are becoming a recognized quality measure for which dialysis facilities might be held accountable. Blood cultures remain the gold standard for diagnosing BSIs and a number of practices can affect the sensitivity and specificity of this important laboratory test. Optimizing the collection of blood cultures can assist providers with interpretation of positive blood cultures and can help minimize the impact of false-positive and false-negative cultures. This review will describe differences between BSI definitions, examine the use of blood cultures to identify these infections including the use of recommended best practices to maximize culture yield, and highlight characteristics that can assist in the clinical interpretation of positive blood cultures.

Diagnostic accuracy of buffy coat culture compared to total blood culture in late-onset sepsis of the newborn

OBJECTIVES

To study the potential of buffy coat culture as a diagnostic tool for neonatal late-onset sepsis.

METHODS

This was a study of diagnostic accuracy in newborn infants born at 28-41 weeks of gestation, weighing >800g, with ≥8 points on the NOSEP-1 scale. Paired samples for total blood culture (TBC) and buffy coat culture were drawn. We established the positivity rate, sensitivity, specificity, predictive values, and likelihood ratios, and compared time to positivity and contamination rates.

RESULTS

Fifty-two newborns were included in the study. Twenty-one TBC and 22 buffy coat cultures were positive. The positivity rate for TBC was 40.4% and for buffy coat culture was 42.3% (p=not significant). Three TBC were positive with negative buffy coat culture. Four buffy coat cultures were positive with negative TBC; Kappa agreement was 0.723, p <0.001. Buffy coat culture sensitivity was 86% (95% confidence interval (CI) 68.5-95.4%), specificity 87% (75.4-93.7%), positive predictive value 82% (65.4-91.1%), negative predictive value 90% (77.9-96.8%), positive likelihood ratio 6.64 (2.79-15.05), and negative likelihood ratio 0.16 (0.05-0.42). We found no difference in time to positivity in hours; Wilcoxon Z=1224, p=0.22. The contamination rate was 1.9% for both methods.

CONCLUSIONS

Buffy coat culture is as good as TBC for the microbiological diagnosis of late-onset sepsis of the newborn. Buffy coat culture allows the use of remaining plasma for further analysis.

Comprehensive analysis of blood culture performed at nine university hospitals in Korea

Background

Optimal blood culture performance is critical for successful diagnosis and treatment of sepsis. To understand the status of blood culture, we investigated several aspects of the procedure at 9 university hospitals.

Methods

The process of ordering blood culture sets and sampling volume for adults and children was investigated from January 2010 to April 2010, while the positive rate of detection and growth of skin contaminants were compared in 2009. Microbial growth in aerobic and anaerobic bottles was investigated prospectively.

Results

A majority of the hospitals used 2 sets of bottles for adults and 1 bottle for children. The average blood volume in each set was 7.7 mL for adults and 2.1 mL for children. The positive rate of microorganisms was 8.0%, and the isolation rate of the normal flora of the skin was 2.1%. Bacterial growth rates in aerobic and anaerobic bottles only were 31.8% and 24.5% respectively.

Conclusions

Ordering blood culture sets and sampling volumes did not comply with CLSI guidelines. However, the rate of positive cultures and skin contamination rates were acceptable. Anaerobic bottles are useful in enhancing the yield of microorganisms.

Prevention of neonatal late-onset sepsis associated with the removal of percutaneously inserted central venous catheters in preterm infants

OBJECTIVES

Indwelling central venous catheters are the most important risk factors for the development of sepsis attributable to coagulase-negative staphylococci among preterm infants admitted to neonatal intensive care units. In addition, removal of a central venous catheter also may cause coagulase-negative staphylococci sepsis, which may be prevented by the short-term administration of an anti-staphylococcal agent during the procedure of removal. The administration of a specific anti-staphylococcal agent (cefazolin) was evaluated for the prevention of central venous catheter removal-associated coagulase-negative staphylococci sepsis.

DESIGN

A prospective, open, randomized, controlled intervention study.

SETTING

Twenty-eight-bed neonatal intensive care unit at a tertiary care children's hospital.

PATIENTS

Eighty-eight preterm infants (gestational age <37 wks) admitted to the neonatal intensive care unit with indwelling percutaneously inserted central venous catheters.

INTERVENTION

From April 2007 to January 2010, infants were randomized to receive two doses of cefazolin during removal of the percutaneously inserted central venous catheter (intervention group, n = 44) or no antimicrobial agent (control group, n = 44). Percutaneously inserted central venous catheter removal-associated sepsis was defined as sepsis occurring <48 hrs after removal of the percutaneously inserted central venous catheter.

MEASUREMENTS AND MAIN RESULTS

Clinical characteristics and central venous catheter duration did not show differences between both groups. Five infants (11%) of the control group developed coagulase-negative staphylococci sepsis <48 hrs after removal of the percutaneously inserted central venous catheter compared to none (0%) in the intervention group (p = .021).

CONCLUSIONS

Two doses of the anti-staphylococcal agent cefazolin during the procedure of removal of a percutaneously inserted central venous catheter were effective in the prevention of coagulase-negative staphylococci sepsis. It is recommended to include this regimen in the guidelines on management of central venous catheters in very-low-birth-weight infants.

Conventional and molecular techniques for the early diagnosis of bacteraemia

Bloodstream infections account for 30-40% of all cases of severe sepsis and septic shock, and are major causes of morbidity and mortality. Diagnosis of bloodstream infections must be performed promptly so that adequate antimicrobial therapy can be started and patient outcome improved. An ideal diagnostic technology would identify the infecting organism(s) and their determinants of antibiotic resistance, in a timely manner, so that appropriate pathogen-driven therapy could begin promptly. Unfortunately, despite the essential information it provides, blood culture, the gold standard, largely fails in this purpose because time is lost waiting for bacterial or fungal growth. Several efforts have been made to optimise the performance of blood culture, such as the development of technologies to obtain rapid detection of microorganism(s) directly in blood samples or in a positive blood culture. The ideal molecular method would analyse a patient's blood sample and provide all the information needed to immediately direct optimal antimicrobial therapy for bacterial or fungal infections. Furthermore, it would provide data to assess the effectiveness of the therapy by measuring the clearance of microbial nucleic acids from the blood over time. None of the currently available molecular methods is sufficiently rapid, accurate or informative to achieve this. This review examines the principal advantages and limitations of some traditional and molecular methods commercially available to help the microbiologist and the clinician in the management of bloodstream infections.

Blood cultures: key elements for best practices and future directions

Bloodstream infections (BSI) cause significant morbidity and mortality among populations worldwide. Blood cultures (BCs) are regarded as the "gold standard" for diagnosis of bacteremia and are among the most important functions of the clinical microbiology laboratory. Significant changes in the methods and techniques of obtaining BCs have occurred since the first inception of BCs into clinical practice. Aside from significant improvements of established, conventional technology, new assays for diagnosis of bacteremia and fungemia, particularly those involving molecular techniques, are now available. BCs must be collected under sterile conditions and guidelines for appropriate collection, processing, and results reporting of BCs have been established. This review provides comprehensive information on optimal BC practices for laboratories, utilizing traditional approaches and emerging technology. As laboratories and clinicians must appreciate the key factors affecting the use of these techniques, improved communication between laboratory personnel and clinicians regarding such elements as duration of incubation, workup of contaminants and critical action value reporting will greatly improve the diagnostic approach to BSI.

Utility of blood cultures in postoperative pediatric intensive care unit patients

OBJECTIVE

To determine the frequency of positive blood cultures in patients with fevers in the initial 48-hour postoperative period.

STUDY DESIGN

All patients who had blood cultures drawn during the initial 48 hours postoperatively while in the pediatric intensive care unit (PICU) at the University of Minnesota Children's Hospital-Fairview during an 18-month period were included in the current study. Six hundred two postoperative patients were admitted to the PICU during the study period. Patients with a temperature >100.4 degrees F and who had blood cultures drawn were identified. Patients for whom the operative procedure was not the first in that admission, those discharged in <48 hours, and those with an indwelling central venous catheter for >24 hours before their admission were excluded.

RESULTS

Sixty-six of these patients were febrile and had blood cultures drawn in the initial 48 hours postoperatively. One hundred eleven blood cultures were obtained. A single (0.9%) blood culture was positive. The cost per positive culture was estimated at $23,532.

CONCLUSIONS

Even in patients admitted to the PICU, fever in the initial 48-hour postoperative period is unlikely to represent bacteremia in low-risk pediatric patients. Blood cultures in these patients are, therefore, unlikely to yield positive results. Procurement of blood cultures in this patient population is not justified. Cessation of the practice of blood culture procurement in this patient population may both focus care and provide enable meaningful cost savings.

Validation criteria for nucleic acid amplification techniques for bacterial infections

Nucleic acid techniques (NATs), such as species-specific and universal polymerase chain reactions (PCRs), are finding ever wider use in the diagnosis of bacterial infection. However, although universal PCR assays, in particular, approach a type of modern Petri dish, they have a number of limitations which restrict their applicability. The sensitivity of universal PCR is lower than that of many species-specific PCRs, and the contamination of samples and PCR reagents with irrelevant DNA from various sources remains a problem. Thus, NATs in general and universal PCR assays in particular require careful validation to be of value for the diagnosis of infection. Validation includes sampling, DNA extraction/isolation, template amplification and visualisation of the results. Furthermore, it implies the establishment of measures of asepsis, the inclusion of positive and negative controls, techniques to optimise the release of DNA from bacterial cells, adequate repetition of the amplification reaction, and routine testing of reagent negative and inhibition controls. Finally, it entails the comparison of results obtained by NATs with those obtained by conventional microbiological methods and matching with clinical evidence of infection. Validation of NATs in clinical diagnosis remains an ongoing challenge. Because of these limitations, NATs can only serve as adjunct tools for the diagnosis of infection in selected cases; they cannot replace conventional culturing techniques.

Identification of central venous catheter-related infections in infants and children

OBJECTIVE

To define central venous catheter-related infections in infants and children for the purpose of enrolling children in sepsis studies, for epidemiology and surveillance studies, and for clinical management.

METHODS

Review of the literature and consensus of experts.

RESULTS

No changes were made to the current Centers for Disease Control and Prevention criteria for defining local catheter infection. Because catheter tips are not available as often in children as in adults, smaller blood volumes are drawn per culture decreasing sensitivity, and antibiotics are rarely withheld, slight modifications to the existing adult Centers for Disease Control and Prevention criteria were made to increase practical use. Catheter-related bloodstream infection was categorized as definite, probable, and possible based on culture results and clinical symptoms.

CONCLUSIONS

For the purposes of enrolling patients with sepsis in clinical trials, only patients who meet criteria for definite catheter-related bloodstream infection should be categorized as having the catheter as the infection source. Because many patients suspected of having catheter-related bloodstream infection do not have positive blood culture results, which makes the confirmation of infection difficult, we recommend that these patients not be enrolled in sepsis trials. Because catheter tips are often not obtained for culture in children, the epidemiology of catheter-associated bloodstream infection (bloodstream infection in a patient who has a central venous catheter and no other obvious source of infection) is better understood than the epidemiology of confirmed catheter-related bloodstream infection in infants and children. Definitions for catheter-related bloodstream infection that compare the through-catheter and peripheral culture for time to positivity or for quantitative growth are unlikely to be falsely positive, but sensitivity requires further validation.

Utility of anaerobic blood cultures in a pediatric emergency department

OBJECTIVES

To determine the frequency with which clinically significant bacterial pathogens are isolated only from the anaerobic blood culture medium in children evaluated for bacteremia and to describe the clinical features associated with these positive cultures.

METHODS

Retrospective review of all blood cultures received from the emergency department in the microbiology laboratory. Clinically significant pathogens were defined as microorganisms that rarely are considered to be contaminants or microorganisms that are recovered from multiple blood cultures or sites from the same individual. Charts of all patients with positive anaerobic cultures for clinically significant pathogens in the presence of negative aerobic cultures were reviewed. The setting was an urban tertiary care pediatric emergency department.

RESULTS

2675 paired blood cultures were performed between January 1, 1998 and December 31, 2000. Growth of a bacterial organism occurred in 595 of the paired samples. Two hundred seventy-eight were clinically significant pathogens. One hundred sixty-two (58.3%) were present in both the aerobic and anaerobic mediums, 85 (30.6%) were only in the aerobic medium, and 31 (11.2%) were only in the anaerobic medium. Most patients with growth only in the anaerobic medium had underlying conditions (ie, central venous line, immunocompromised, congenital heart disease, liver disease, age < 3 months). No obligate anaerobic organisms were detected.

CONCLUSIONS

In a pediatric emergency department setting, almost all pathogenic bacteria were isolated from aerobic culture mediums in otherwise healthy children. The yield of routinely performed anaerobic blood cultures is low. In previously healthy children, it may be optimal to inoculate the entire blood volume obtained into the aerobic medium.

Diagnostic methods. Current best practices and guidelines for isolation of bacteria and fungi in infective endocarditis

As the etiological character of IE changes, the microbiological tools used to confirm the diagnosis have also evolved. Here the authors have reviewed the current methods for optimal laboratory diagnosis of bacterial and fungal endocarditis using traditional growth-based technologies and offered good practice guidelines and recommendations. Newer techniques will be required to improve sensitivity of detection for known organisms and to identify emerging or as-yet unknown pathogens (see article by Lepidi et al in this issue).

Diagnostic methods current best practices and guidelines for isolation of bacteria and fungi in infective endocarditis

This article addresses the clinical need for accurate detection of bacteria and fungi that may cause infective endocarditis (IE). The pathophysiology of bacteremia during endocarditis is reviewed to provide an understanding of how current diagnostic methods may be used to determine the etiologic diagnosis. The critical contribution of microbiologic findings to the current clinical diagnostic criteria is emphasized. Finally, "best practices" recommendations are presented to optimize the likelihood of reaching a correct etiologic diagnosis while minimizing the number of "culture-negative" cases.

Laboratory diagnosis of bacteremia and fungemia

Many of the variables that affect the laboratory diagnosis of bacteremia and fungemia have been addressed in this article. Whereas the scientific basis and principles for blood cultures are well-established, and the methodology has improved, the diagnosis of bacteremia and fungemia still depends greatly on the care that is taken in obtaining the specimens of blood and the skill of the clinician in interpreting positive results.

Comparison of the BacT/Alert PF pediatric FAN blood culture bottle with the standard pediatric blood culture bottle, the Pedi-BacT

The performance of the BacT/Alert PF (Organon-Teknika Corp., Durham, N.C.), a new nonvented pediatric FAN blood culture bottle, was compared to that of the original pediatric bottle, the Pedi-BacT, with matched aerobic cultures obtained from two separate facilities. A total of 244 clinically significant isolates were recovered from 4,015 compliant pairs. Among the positive cultures, 170 (70%) isolates were detected in both the BacT/Alert PF and the Pedi-BacT bottles, while 47 (19%) isolates were recovered in the BacT/Alert PF bottle only and 27 (11%) isolates were recovered in the Pedi-BacT bottle only. Although isolation of specific microorganisms was comparable for the two bottles, the total number of organisms recovered by the BacT/Alert PF was greater than that by the Pedi-BacT (P = 0.0272). In addition, more organisms were recovered by the BacT/Alert PF bottle from the blood of patients receiving antimicrobial therapy (P = 0.0180). Overall time to detection was similar for the two bottles; however, a significantly decreased mean time to detection was recorded for yeast from the BacT/Alert PF bottle (22.9 h; P = 0.0001) and staphylococci from the Pedi-BacT bottle (22.5 h; P = 0.0056). One false-negative culture and five false-positive cultures occurred with the Pedi-BacT bottle, compared to one false-positive culture with the BacT/Alert PF bottle. The BacT/Alert PF bottle is a reliable blood culture bottle for pediatric blood culture specimens and may offer improved recovery of microbes from patients on antimicrobial therapy. The use of the nonvented bottle will both facilitate bottle processing and decrease expenditures for materials due to the elimination of the venting needles required for the original vented bottles.

Bacterial isolates from blood and their susceptibility patterns in critically ill foals: 543 cases (1991-1998)

OBJECTIVE

To assess microorganisms isolated from blood specimens obtained from critically ill neonatal foals and to evaluate their antimicrobial susceptibility patterns.

DESIGN

Retrospective study.

ANIMALS

543 neonatal foals.

PROCEDURE

Medical records of foals that were < 1 month old and were admitted to a referral neonatal intensive care unit were reviewed for results of bacteriologic culture of blood and antimicrobial susceptibility patterns.

RESULTS

At least 1 microorganism was isolated from 155 of 543 (28.5%) foals. Escherichia coli was the most commonly isolated bacterium. A single gram-positive organism was detected in 49 foals. Although 90% of the E coli isolates were susceptible to amikacin, some gram-negative and gram-positive organisms had resistance against multiple antimicrobials.

CONCLUSIONS AND CLINICAL RELEVANCE

Gram-negative bacteria remain the most common isolates from blood of neonatal foals; however, gram-positive organisms were also found, and with greater prevalence than reported elsewhere. Susceptibility patterns may vary, and resistance to multiple antimicrobials may develop. This is especially true for organisms such as Enterobacter spp and Enterococcus spp. Prudent empirical treatment for neonatal sepsis should include broad-spectrum antimicrobials.

Frequency of low-level bacteremia in children from birth to fifteen years of age

A single blood culture inoculated with a small volume of blood is still frequently being used for the diagnosis of bacteremia in children because of the continued belief by many that bacteria are usually found in high concentrations in the blood of pediatric patients with sepsis. To determine the importance of both blood volume cultured and the number of culture devices required for the reliable detection of pathogens in our pediatric population, blood from children from birth to 15 years of age and with suspected bacteremia at York Hospital (a 500-bed community hospital) was inoculated into at least a Pediatric Isolator (Wampole Laboratories; 1.5 ml of blood) or a standard Isolator (10 ml of blood) and a bottle of ESP anaerobic broth (Trek Diagnostic Systems; 0.5 to 10 ml of blood). The use of a second Isolator and additional aerobic and anaerobic bottles and the total blood volume recommended for cultures (2 to 60 ml) depended on the weight and total blood volume of each patient. One hundred forty-seven pathogens were recovered from the blood of 137 (3.6%) of 3,829 children for whom culturing was done. Of 121 septic episodes for which the concentration of pathogens in the blood could be determined using Isolators, 73 (60. 3%) represented low-level bacteremia (</=10 CFU/ml of blood), including 28 pathogens (23.1%) which were detected at concentrations of only </=1.0 CFU/ml. Of 144 septic episodes for which two or more culture devices (Isolators and/or bottles) were inoculated, 85 (59%) were associated with false-negative results from one or more of the culture devices. Of the 128 children for whom antibiotic therapy records were complete, therapy was either started or changed for 88 (68.8%) following notification of positive blood cultures. Low-level bacteremia was common in our pediatric population, requiring the culturing of up to 4 or 4.5% of a patient's total blood volume for the reliable detection of pathogens and appropriate, timely changes in empiric therapy.

Survey of blood cultures from five community hospitals in south-western Sydney, Australia, 1993-1994

BACKGROUND

Blood culture results have profound implications for patients. Comprehensive overviews of blood cultures have been uncommon, and focused on tertiary referral hospitals.

AIM

To present a review of blood culture results from a laboratory servicing community hospitals in Sydney, Australia.

METHODS

Retrospective chart review of patients with positive blood cultures from 1 June 1993 to 31 May 1994.

RESULTS

During the survey period there were 107,382 hospital admissions; 12,109 blood culture sets from 9292 patients were processed. Of these 1197 sets were positive, representing 974 febrile episodes in 923 patients. There were 476 episodes of contamination. Of the episodes of true bacteraemia, Escherichia coli was isolated in 139, Staphylococcus aureus in 91 (22 methicillin-resistant), other enterobacteriaceae in 60, and Streptococcus pneumoniae in 5 1. The diagnoses attributable to bacteraemia included intravenous catheter-related sepsis (122 episodes), urinary tract infection (88), bacteraemia from unknown source (79), intra-abdominal and biliary sepsis (91), pneumonia (35), and meningitis (21). Sixty-eight patients died directly due to bacteraemia. Multivariate analysis showed underlying disease (OR 3.97) or shock (OR 28.1) predicted death. Blood cultures confirmed clinical diagnoses in 258 episodes, but made a de novo diagnosis in 205 episodes.

CONCLUSIONS

This study describes the clinical and laboratory features of bacteraemias occurring in smaller public hospitals, as distinct from tertiary referral centres. It demonstrated that intravenous catheter-related sepsis was very common in smaller hospitals. The clinical diagnosis was frequently confirmed, and a de novo diagnosis was often established by a positive blood culture. Unfortunately nearly half the positive blood cultures represented contamination.

PCR and blood culture for detection of Escherichia coli bacteremia in rats

Critically ill patients often develop symptoms of sepsis and therefore require microbiological tests for bacteremia that use conventional blood culture (BC) techniques. However, since these patients frequently receive early empirical antibiotic therapy before diagnostic procedures are completed, examination by BC can return false-negative results. We therefore hypothesized that PCR could improve the rate of detection of microbial pathogens over that of BC. To test this hypothesis, male Wistar rats were challenged intravenously with 10(6) CFU of Escherichia coli. Blood was then taken at several time points for detection of E. coli by BC and by PCR with E. coli-specific primers derived from the uidA gene, encoding beta-glucuronidase. In further experiments, cefotaxime (100 or 50 mg/kg of body weight) was administered intravenously to rats 10 min after E. coli challenge. Without this chemotherapy, the E. coli detection rate decreased at 15 min and at 210 min after challenge from 100% to 62% of the animals with PCR and from 100% to 54% of the animals with BC (P, >0.05). Chemotherapy decreased the E. coli detection rate at 25 min and at 55 min after challenge from 100% to 50% with PCR and from 100% to 0% with BC (P, <0.05). Thus, at clinically relevant serum antibiotic levels, PCR affords a significantly higher detection rate than BC in this rat model. The results suggest that PCR could be a useful adjunct tool supplementing conventional BC techniques in diagnosing bacteremia.

Intravenous catheter blood cultures: utility and contamination

OBJECTIVE

In pediatrics, blood cultures (BCs) are often drawn as intravenous (IV) catheters are placed. This routine minimizes the number of painful and often difficult punctures a child must undergo but results in the discarding of multiple BC bottles when these cultures are later determined to be unnecessary. If the contamination rate of BCs drawn through an indwelling IV did not exceed the contamination rate of BCs drawn at the time of IV placement, BCs could be drawn from the IV without subjecting the patient to another venipuncture. This study was done to compare the contamination rates of BCs drawn by these two methods. Additionally, we sought to determine if the collection of two BCs enhances pathogen recovery.

METHODS

Prospective comparison of contamination and bacteremia rates of BCs drawn by two different methods: the first BC was drawn at the time of IV line placement and the second BC was drawn from the previously placed IV at a later time. Setting. Urban pediatric emergency department with an annual census of 40 000.

PARTICIPANTS

One thousand five hundred sixty-four patients between the ages of 3 days and 22.1 years. The median age was 2.2 years. Sixty-four patients were excluded because we were unable to draw the second BC. Forty-six percent of eligible patients (n = 690) were girls.

RESULTS

Fifty-seven (1.9%) of 3000 grew contaminants: 27 in the first and 30 in the second BC for contamination rates of 1.8% and 2.0%. Thirty-eight (1.3%) of 3000 BCs grew pathogens: 24 represent 12 patients with growth in two out of two cultures and 14 represent 14 patients with growth in one out of two cultures. Pathogen rates were 1.1% (16/1500) with one BC per patient and 1.7% (22/1500) with two BCs per patient.

CONCLUSIONS

There is no difference in the contamination rates of two BCs drawn from the same site at two different times. The collection of two BCs per patient may enhance pathogen recovery.

Community-acquired bacteremia in human immunodeficiency virus-infected children in Harare, Zimbabwe

BACKGROUND

HIV infection is common in mothers and their children in Zimbabwe, and HIV-infected children are particularly susceptible to bacterial infections. There is little information on the etiology and outcome of HIV-related bacteremia in African children.

METHODS

Blood cultures from 309 hospitalized children in Zimbabwe, of whom 168 were diagnosed as having HIV, were examined for pathogens. The association among significant bacteremia, HIV infection and mortality was assessed in these children.

RESULTS

The most common isolates were coagulase-negative staphylococci (31 children, 25 clinically significant), Staphylococcus aureus (22 children) and Streptococcus pneumoniae (20 children). Nontyphoidal Salmonella (10 children), Escherichia coli (4 children) and Klebsiella sp. (4 children) were the most frequent Gram-negative bacteria. Two children had Rhodococcus equi pneumonia. HIV-infected children showed increased risk of bacteremia (odds ratio (OR) = 2.68), especially if younger than 18 months of age (OR = 2.94), and high risk of enterobacteremia (OR = 15.76). There was no significant association of bacteremia with nutritional status. Mortality was 17% overall but was higher in HIV-infected children up to 6 months of age (OR = 2.81) and in bacteremic children of any age (OR = 2.03).

CONCLUSIONS

Prompt recognition of pathogens and early administration of appropriate antimicrobials is important in reducing the morbidity and mortality associated with bacteremia in HIV-infected children in Africa.

Volume of blood required to detect common neonatal pathogens

OBJECTIVE

To determine the minimum volume of blood and the absolute number of organisms required for detection of bacteremia and fungemia by an automated colorimetric blood culture system (BacT/Alert, Organon Teknika).

DESIGN

Common neonatal pathogens, Escherichia coli, Streptococcus agalactiae (group B streptococcus (GBS): one American Type Culture Collection (ATCC) strain and one clinical isolate), Staphylococcus epidermidis, and Candida albicans, were seeded into blood to produce bacteremia or fungemia with low colony counts (1 to 3 colony-forming units (CFU) per milliliter) and ultra-low colony counts (<1 CFU/ml). For each organism, 96 culture bottles were inoculated with either 0.25, 0.5, 1.0, or 4.0 ml of the two seeded blood concentrations. Blood culture bottles were incubated in the BacT/Alert device for 5 days, and time to positivity was noted when applicable. All bottles were subcultured on plated media.

DATA ANALYSIS

The Poisson statistic was used to calculate the probability of finding at least one viable CFU per inoculated culture bottle. The fraction of culture bottles with positive findings per group was divided by the probability of one or more organisms present to give the positivity index.

RESULTS

Plated subculture identified no growth of organisms not detected by the colorimetric detection system. The false-positive rate for the automated device was less than 1%. The positivity index for the GBS clinical isolate was 1.13, for the GBS ATCC isolate 0.96, for S. epidermidis 0.94, for C. albicans 0.97, and for E. coli 0.95. There was a statistically significant difference with time to positivity and inocula volume (p <0.01), but the difference was not clinically important.

CONCLUSIONS

If one or two viable colony-forming units are in the blood inoculated into culture media, the BacT/Alert system will detect growth rapidly. Because there appears to be a sizable subset of neonates who are at risk of sepsis with a colony count less than 4 CFU/ml, then a 0.5 ml inoculum of blood into the culture media is inadequate for sensitive and timely detection of bacteremia. One to two milliliters of blood should increase microorganism recovery in the face of low-colony-count sepsis.

Yield of positive blood cultures in pediatric oncology patients by a new method of blood culture collection

BACKGROUND

The optimal number of blood cultures and the volume of blood for pediatric blood cultures have not been defined. In 1990 such criteria were established at our institution. We retrospectively reviewed records of all pediatric oncology patients who were admitted for febrile episodes in 1989 and in 1991 and 1992 to determine whether there was an increase in the detection of bacteremia and fungemia.

METHODS

Blood was drawn via venipuncture and central intravascular catheters and inoculated into the designated blood culture bottles. Each patient had a minimum of two separate blood draws, i.e. two separate cultures; the volume was determined by the patient's weight. In all cases < 1% of the patient's blood volume was drawn per culture. Patients' records were reviewed regarding type of malignancy, chemotherapy and neutropenia.

RESULTS

The rate of bacteremic patients increased from 12% (13 of 113) in 1989 to 22% (27 of 123) in 1991. This increase continued through 1992 with 23% (27 of 118) of patients having positive blood cultures. Gram-positive bacteria predominated throughout the study period.

CONCLUSIONS

Although factors such as more aggressive chemotherapy or a different spectrum of malignant diseases may contribute to the statistically significant increase in identification of bacteremic patients, a standardized method of blood culture collection is merited. The consistent volumes of blood per culture and the minimum of two cultures per febrile episode follow the principles of blood culture collection established for adults. The same principles should apply to pediatric patients.

Value of routine anaerobic blood cultures for pediatric patients

OBJECTIVE

Anaerobic bacteremia rarely occurs in children. Therefore we assessed the usefulness of routinely obtaining anaerobic blood cultures in our pediatric patients.

STUDY DESIGN

Records of 9360 paired aerobic anaerobic blood culture bottles (Bactec NR660 System) containing blood specimens from pediatric inpatients and outpatients at Duke University Medical Center, Durham, N.C., were reviewed retrospectively. Yield and speed of detection were calculated for each bottle and compared for statistical significance by the McNemar test.

RESULTS

A total of 723 clinically important microorganisms were isolated; only 15 (2.1%) were strict anaerobes. Significantly more microorganisms (p < 0.001), especially staphylococci, nonfermenting gram-negative rods, enteric gram-negative rods, and yeasts, were detected by use of the aerobic bottle. The anaerobic bottle was important in identifying an anaerobic microorganism as the cause of sepsis in only five patients, all of whom were at increased risk of having anaerobic infection.

CONCLUSIONS

Anaerobic blood cultures are rarely helpful in the majority of pediatric patients and usually show positive results only in clinical settings associated with anaerobic infection. Microorganisms that prefer an aerobic environment, such as Pseudomonas aeruginosa and yeasts, are now far more common than anaerobes in children; aerobic culturing of the entire volume of blood collected might increase the yield from pediatric blood cultures.