Assessment of the yield of anaerobic blood cultures

Pediatric Anaerobic Blood Culture Practices in Industrialized Countries

BACKGROUND

Routine anaerobic blood culture collection in febrile children is controversial, as clinicians try to account for the severe but relative infrequency of anaerobic bacteremia. Furthermore, clinical and laboratory practice variation among institutions may lead to potentially inaccurate epidemiological data. Our goal was to assess blood culture practices in pediatric patients throughout an international network of hospitals in industrialized countries.

METHODS

We conducted a survey of current clinical and laboratory practice patterns in a convenience sample of international institutions participating in 6 pediatric emergency research networks in the US, Canada, Europe, Australia, and New Zealand. A lead clinician at each institution queried institutional practices from the emergency department, pediatric intensive care unit, and oncology medical directors. The microbiology director at each institution completed the laboratory survey.

RESULTS

Sixty-five of 160 (41%) invited institutions participated in the survey. Routine anaerobic blood cultures are collected in 30% of emergency departments, 30% of intensive care units, and 48% of oncology wards. Reasons for restricting anaerobic culture collection included concerns regarding blood volume (51%), low pretest probability (22%), and cost-effectiveness (16%). The most common reasons institutions allow for selectively obtaining anaerobic cultures are clinical suspicion (64%) and patients who are immunosuppressed (50%). The microbiology survey showed variation in systems, although most use the BACTEC™ culture system and MALDI-TOF for organism identification.

CONCLUSIONS

There is broad variation in anaerobic blood culture practices among a network of pediatric hospitals in industrialized countries.

Role of Anaerobic Blood Cultures in Neonatal Bacteremia

BACKGROUND

Evaluation for neonatal sepsis routinely includes performing both aerobic and anaerobic blood cultures despite our lack of knowledge of the true incidence of anaerobic bacteremia in this age group and the consequences of not performing these paired cultures.

METHODS

We performed a retrospective review of all blood cultures performed for neonates in a children's hospital. Clinically significant pathogens were defined as microorganisms that rarely are considered to be contaminants, that were recovered from multiple blood cultures or sites, or were considered significant according to the patient's attending physician. The chart of every patient with positive culture results was reviewed for patient characteristics.

RESULTS

A total of 662 culture sets among 403 patients were obtained between November 1, 2013, and April 30, 2015. A clinically significant organism was isolated from 64 (9.7%) culture sets from 25 patients (1.9% contamination rate). A total of 56 organisms were isolated; 35 (62.5%) grew from both the aerobic and anaerobic bottles, 19 (33.9%) grew from the anaerobic bottle alone, and 2 (3.6%) grew from the aerobic bottle alone. One (0.2%) obligate anaerobic bacterium (Clostridium symbiosum) was identified.

CONCLUSIONS

Although the incidence of anaerobic bacteremia in neonates is rare, anaerobic culture remains important in this population, given the increased yield of both aerobic and facultative anaerobic organisms isolated from anaerobic blood culture bottles.

[Diagnostic reliability of anaerobic blood cultures in bacteremias from a critical care unit]

BACKGROUND AND OBJECTIVE

This is a descriptive study of bacteraemias diagnosed in ICU with an analysis of the diagnostic reliability of anaerobic blood cultures.

PATIENTS AND METHOD

Analysis of all positive blood cultures in an Intensive Care Unit from May 2005 to October 2007.

RESULTS

The overall incidence of true bacteraemia was 6,1% of admissions. Out of 100 patients, there were 73 bacteraemias and 52 contaminated cultures. Samples with contaminated cultures were drawn 6,27 days earlier (CI 95% 0,61-11,94 Sig:0,03) than true bacteraemia. Most frequent micro organisms were cocci gram positive: 43 cases (58,9%) (coagulase-negative staphylococci was the most frequent: 30 or 41% of all bacteraemia)) Sig=0,001 in relation with gram negatives. Anaerobic micro organisms were not detected. Candidemias were found in 10 cases (13,7%). The most frequent causes of bacteraemia in this study were catheter-related infections with 36 cases (49,3% Sig<0,005), followed by digestive origin infections in 14 (19,2%). Of all bacteremic episodes (73 bacteraemia), 66 (90,4%) were isolated in aerobic blood cultures, and 58 (79,5%) were in anaerobic ones, with a difference of 10,9% Sig:0,06. When only intrahospitalary bacteraemias were analyzed, there was a difference of 13,56% of more yields in aerobic blood cultures; Sig:0,04 (IC 95% 0,8%-26%)). Candidemias were isolated only in aerobic blood cultures; Sig:0,001. When analyzing coagulase negative staphylococci, there were 30 bacteraemias and 41 contaminated samples. 62 (87,3%) were isolated in aerobic blood cultures and 50 (70,4%) in anaerobic ones, with a difference of 16,9% Sig=0,01,CI 95%(3%-30%).

CONCLUSIONS

In the Critical Care Unit, it would be possible to change the anaerobic blood cultures by aerobic ones to diagnose bacteraemias of intrahospitalary acquisition. This fact should be analyzed with others studies.

Is anaerobic blood culture necessary? If so, who needs it?

BACKGROUND

The role of anaerobic blood cultures is not validated, although they are drawn routinely.

METHODS

We performed a retrospective chart review at a private hospital in Japan for patients admitted between July 1, 2004 to June 30, 2005 to determine patient characteristics resulting in anaerobic blood culture.

RESULTS

During the study period, 17,775 blood culture bottles were sent for the analysis, and 2132 bottles (12.0%) were positive for microbial growth. Bacteria were grown from 958 anaerobic bottles (44.7%), and 719 (33.7%) of those were judged to represent real infections, which accounted for 410 cases of bacteremia. Only 47 cases (11.5%) were detected by anaerobic cultures alone. Among those 47, obligate anaerobes represented 12 cases. Clinical evaluation could have predicted 7 of 12 cases of obligate anaerobic bacteremia. In the remaining 5 cases, the source of bacteremia was unclear. There were 2.7 cases of anaerobic bacteremia per 1000 blood cultures. The mortality attributable to anaerobic bacteremia was 50%. Among bacteremic cases not caused by obligate anaerobes yet diagnosed solely by anaerobic bottles, either the standard 2 sets of blood were not taken or their clinical outcomes were favorable.

CONCLUSION

Anaerobic blood culture can be avoided in most cases. Anaerobic blood culture may be most helpful when (1) bacteremia because of obligate anaerobes is clinically suspected, (2) patients are severely immunocompromised, and (3) source of bacteremia is not identified by clinical evaluation.

Analysis of anaerobic blood cultures in burned patients

The utility of anaerobic blood culturing is often debated in the general population, but there is limited data on the modern incidence, microbiology, and utility of obtaining routine anaerobic blood cultures for burned patients. We performed a retrospective review of the burned patients electronic medical records database for all blood cultures drawn between January 1997 and September 2005. We assessed blood cultures for positivity, organisms identified, and growth in aerobic or anaerobic media. 85,103 blood culture sets were drawn, with 4059 sets from burned patients. Three hundred and forty-five single species events (619 total blood culture isolates) were noted in 240 burned patients. For burned patients, four isolates were obligate anaerobic bacteria (all Propionibacterium acnes). Anaerobic versus aerobic culture growth was recorded in 310 of 619 (50.1%) burned patient blood culture sets. 46 (13.5%) of the identified organisms, most of which were not obligate anaerobic bacteria, were identified from solely anaerobic media. The results of our study suggest that the detection of significant anaerobic bacteremia in burned patients is very rare and that anaerobic bottles are not needed in this population for that indication. However anaerobic blood cultures systems are also able to detect facultative and obligate aerobic bacteria; therefore, the deletion of the anaerobic culture medium may have deleterious clinical impact.

Relevance of routine use of the anaerobic blood culture bottle

Using the BacT/Alert automated system, we conducted a 1-year retrospective study on blood cultures, focusing on the relevance of routine use of the anaerobic bottle. The rate of patients with positive blood cultures was 19.7%. Among these, 13.5% had a positive anaerobic bottle in the absence of any aerobic bottle, and 2/3 of these grew with nonobligate anaerobes. These patients were hospitalized in 20 out of 26 wards of the hospital group. For 65.4% of the monomicrobial-positive blood cultures growing Enterobacteriaceae, the anaerobic bottle detected growth earlier than the corresponding aerobic bottle. These data suggest that, in our institution, the use of an anaerobic bottle is still relevant.

Value of anaerobic blood cultures in pediatrics

The aim of the study presented here was to evaluate the utility of anaerobically incubated blood cultures for detecting infections in pediatric patients. During a 2-year period 9,165 pediatric blood samples were processed, and significant microorganisms were recovered from 497 (5.4%) of them. Only two of the microorganisms isolated were strictly anaerobic. Of the total isolates, 13% were detected in anaerobic bottles solely. Considering that the quantity of blood available from pediatric patients for blood cultures is usually small, it may be reasonable to limit the use of anaerobic blood cultures to patients with the highest risk.

Diagnosis of infection in sepsis: An evidence-based review

OBJECTIVE

In 2003, critical care and infectious disease experts representing 11 international organizations developed management guidelines for the diagnosis of infection in sepsis that would be of practical use for the bedside clinician, under the auspices of the Surviving Sepsis Campaign, an international effort to increase awareness and improve outcome in severe sepsis.

DESIGN

The process included a modified Delphi method, a consensus conference, several subsequent smaller meetings of subgroups and key individuals, teleconferences, and electronic-based discussion among subgroups and among the entire committee.

METHODS

The modified Delphi methodology used for grading recommendations built on a 2001 publication sponsored by the International Sepsis Forum. We undertook a systematic review of the literature graded along five levels to create recommendation grades from A to E, with A being the highest grade. Pediatric considerations to contrast adult and pediatric management are in the article by Parker et al. on p. S591.

CONCLUSIONS

Obtaining a precise bacteriological diagnosis before starting antibiotic therapy is, when possible, of paramount importance for the success of therapeutic strategy during sepsis. Two to three blood cultures should be performed, preferably from a peripheral vein, without interval between samples to avoid delaying therapy. A quantitative approach is preferred in most cases when possible, in particular for catheter-related infections and ventilator-associated pneumonia. Diagnosing community-acquired pneumonia is complex, and a diagnostic algorithm is proposed. Appropriate samples are indicated during soft tissue and intraabdominal infections, but cultures obtained through the drains are discouraged.

Anaerobic bacteremia: the yield of positive anaerobic blood cultures: patient characteristics and potential risk factors

The anaerobic blood culture (AN) bottle is routinely used in Japan with little discussion as to its justification or validity. We retrospectively studied the AN bottle yield of obligate anaerobes and the characteristics of, and potential risk factors in, patients with anaerobic bacteremia during a 2-year period (1999-2000) at four university hospitals and one community hospital. Thirty-four of 18,310 aerobic and anaerobic blood culture sets from 6,215 patients taken at the university hospitals, and 35 of 2,464 samples taken from 838 patients at the community hospital, yielded obligate anaerobes. Bacteroides species and Clostridium species accounted for 60% of the isolates. Fifty-seven patients from 69 blood culture sets containing anaerobes had clinically significant anaerobic bacteremia. Among these 57 patients, 24 (49%) were oncology patients, 40 (70%) had an obvious source of anaerobic infection, 15 (26%) had recent surgery and/or were in an immunosuppressed state. We concluded that the recovery rate of obligate anaerobes isolated from AN bottles was low, and the patients with anaerobic bacteremia had limited number of underlying diseases or potential risk factors for anaerobic infections. Therefore, anaerobic blood cultures may be selectively used according to the potential risk for anaerobic infections.

Use of anaerobically incubated media to increase yield of positive blood cultures in children

During a 3-year period we received 10024 blood samples for culture from pediatric patients. Overall 181 episodes of significant bacteremia were documented. During the study period we would have missed 35 (19%) of all significant episodes of pediatric bloodstream infections if we had not been using the anaerobically incubated blood bottle. Anaerobically incubated blood samples are also necessary in the pediatric population.

Controlled clinical comparison of BACTEC plus anaerobic/F to standard anaerobic/F as the anaerobic companion bottle to plus aerobic/F medium for culturing blood from adults

To determine the optimal anaerobic companion bottle to pair with BACTEC Plus Aerobic/F medium for recovery of pathogenic microorganisms from adult patients with bacteremia and fungemia, we compared Plus Anaerobic/F bottles with Standard Anaerobic/F bottles, each of which was filled with 4 to 6 ml of blood. The two bottles were paired with a Plus Aerobic/F bottle filled with 8 to 12 ml of blood. A total of 14,011 blood culture sets were obtained. Of these, 11,583 sets were received with all three bottles filled adequately and 12,257 were received with both anaerobic bottles filled adequately. Of 818 clinically important isolates detected in one or both adequately filled anaerobic bottles, significantly more staphylococci (P < 0.001), streptococci (P < 0.005), Escherichia coli isolates (P < 0.02), Klebsiella pneumoniae isolates (P < 0.005), and all microorganisms combined (P < 0.001) were detected in Plus Anaerobic/F bottles. In contrast, significantly more anaerobic gram-negative bacilli were detected in Standard Anaerobic/F bottles (P < 0.05). Of 397 unimicrobial episodes of septicemia, 354 were detected with both pairs, 30 were detected with Plus Aerobic/F-Plus Anaerobic/F pairs only, and 13 were detected with Plus Aerobic/F-Standard Anaerobic/F pairs only (P < 0.05). Significantly more episodes of bacteremia caused by members of the family Enterobacteriaceae (P < 0.05) and aerobic and facultative gram-positive bacteria (P < 0.025) were detected with Plus Anaerobic/F bottles only. In a paired-bottle analysis, 810 of 950 isolates were recovered from both pairs, 90 were recovered from Plus Aerobic/F-Plus Anaerobic/F pairs only, and 50 were recovered from Plus Aerobic/F-Standard Anaerobic/F pairs only (P < 0.001). Paired Plus Aerobic/F-Plus Anaerobic/F bottles yielded significantly more staphylococci (P < 0.001), streptococci (P < 0.05), and members of the family Enterobacteriaceae (P <0.001). We conclude that Plus Anaerobic/F bottles detect more microorganisms and episodes of bacteremia and fungemia than Standard Anaerobic/F bottles as companion bottles to Plus Aerobic/F bottles in the BACTEC 9240 blood culture system.