The utility of anaerobic blood culture in detecting facultative anaerobic bacteremia in children

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.

Blood Culture Utilization in the Hospital Setting: a Call for Diagnostic Stewardship

There has been significant progress in detection of bloodstream pathogens in recent decades with the development of more sensitive automated blood culture detection systems and the availability of rapid molecular tests for faster organism identification and detection of resistance genes. However, most blood cultures in clinical practice do not grow organisms, suggesting that suboptimal blood culture collection practices (e.g., suboptimal blood volume) or suboptimal selection of patients to culture (i.e., blood cultures ordered for patients with low likelihood of bacteremia) may be occurring. A national blood culture utilization benchmark does not exist, nor do specific guidelines on when blood cultures are appropriate or when blood cultures are of low value and waste resources. Studies evaluating the potential harm associated with excessive blood cultures have focused on blood culture contamination, which has been associated with significant increases in health care costs and negative consequences for patients related to exposure to unnecessary antibiotics and additional testing. Optimizing blood culture performance is important to ensure bloodstream infections (BSIs) are diagnosed while minimizing adverse events from overuse. In this review, we discuss key factors that influence blood culture performance, with a focus on the preanalytical phase, including technical aspects of the blood culture collection process and blood culture indications. We highlight areas for improvement and make recommendations to improve current blood culture practices among hospitalized patients.

Neonatal blood culture inoculant volume: feasibility and challenges

BACKGROUND

Clinicians often express concerns about poor sensitivity of blood cultures in neonates resulting from inadequate inoculant volumes. Our objective was to determine the inoculant volume sent for neonatal sepsis evaluations and identify areas of improvement.

METHODS

Single-center prospective observational study of infants undergoing sepsis evaluation. Blood volume was determined by clinician documentation over 21 months, and additionally by weighing culture bottles during 12 months. Adequate volume was defined as ≥1 mL total inoculant per evaluation. For first-time evaluations, local guidelines recommend sending an aerobic-anaerobic pair with 1 mL inoculant in each.

RESULTS

There were 987 evaluations in 788 infants. Clinicians reported ≥1 mL total inoculant in 96.9% evaluations. Among 544 evaluations where bottles were weighed, 93.4% had ≥1 mL total inoculant. Very low birth weight infants undergoing evaluations >7 days after birth had the highest proportion of inadequate inoculants (14.4%). Only 3/544 evaluations and 26/1011 bottles had total inoculant <0.5 mL. Ninety evaluations had <1 mL in both aerobic and anaerobic bottles despite a total inoculant volume that allowed inoculation of ≥1 mL in one of the bottles.

CONCLUSIONS

Obtaining recommended inoculant volumes is feasible in majority of neonates. Measuring inoculant volumes can focus improvement efforts and improve test reliability.

IMPACT

Clinicians express concern about the unreliability of neonatal blood cultures because of inadequate inoculant volume. We investigated over 900 evaluations and found >90% of evaluations have ≥1 mL inoculant. Monitoring adequacy of blood culture technique can identify areas of improvement and may allay concerns about blood culture reliability. Current recommendations for adequate inoculant volume for blood cultures are met in a majority of neonates. Areas of improvement include preterm late-onset sepsis evaluations and distribution techniques during inoculation.

The Addition of Anaerobic Blood Cultures for Pediatric Patients with Concerns for Bloodstream Infections: Prevalence and Time to Positive Cultures

Anaerobes are an important but uncommon cause of bloodstream infections (BSIs). For pediatric patients, routine inclusion of an anaerobic blood culture alongside the aerobic remains controversial. We implemented automatic anaerobic blood culture alongside aerobic blood cultures in a pediatric emergency department (ED) and sought to determine changes in recovery of obligate and facultative anaerobes. This was a cohort study in a pediatric ED (August 2015 to July 2018) that began in February 2017. Blood culture positivity results for true pathogens and contaminants were assessed, along with a secondary outcome of time to positivity (TTP) of blood culture. A total of 14,180 blood cultures (5,202 preimplementation and 8,978 postimplementation) were collected, with 8.8% (456) and 7.1% (635) positive cultures in the pre- and postimplementation phases, respectively. Of 635 positive cultures in the postimplementation phase, aerobic blood cultures recovered 7.6% (349/4,615), whereas anaerobic blood cultures recovered 6.6% (286/4,363). In 211/421 (50.0%) paired blood cultures, an organism was recovered in both cultures. The number of cases where organisms were only recovered from an aerobic or an anaerobic bottle in the paired cultures were 126 (30.0%) and 84 (20.0%), respectively. The TTP was comparable regardless of bottle type. Recovery of true pathogens from blood cultures was approximately 7 h faster than recovery of contaminants. Although inclusion of anaerobic blood cultures only recovered 2 (0.69%) obligate anaerobes, it did allow for recovery of clinically significant pathogens that were negative in aerobic blood cultures and supports the routine collection of both bottles in pediatric patients with a concern of bloodstream infections.

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.

Yield of Anaerobic Blood Cultures in Pediatric Emergency Department Patients

BACKGROUND

Anaerobic bacteremia is rare in children and current recommendations advocate against the routine use of anaerobic cultures in children. However, the incidence of anaerobic bacteremia and the utility of anaerobic blood cultures in children have not been assessed in recent years. Our pediatric emergency department (PED) policy still supports the use of both aerobic and anaerobic blood cultures in all cases of suspected bacteremia. This allowed us to re-evaluate the yield of anaerobic cultures in PED settings.

METHODS

Retrospective data of all blood cultures taken in the PED in a single tertiary center from 2002 to 2016 were collected. The incidence and characteristics of children with positive anaerobic blood cultures were assessed. Risk factors for anaerobic bacteremia were defined.

RESULTS

Of the 68,304 blood culture sets taken during the study period, 971 (1.42%) clinically significant positive cultures were found. Pathogenic obligatory anaerobic bacteria were isolated in 33 (0.05%) cultures. The leading risk factors for anaerobic bacteremia were head and neck abscess and intra-abdominal infection. Of all the true positive cultures, 187 (22%) were only detected in the anaerobic culture and would have otherwise been missed.

CONCLUSIONS

True anaerobic bacteremia is extremely rare in children admitted to the PED. Nevertheless, using anaerobic cultures may increase the overall yield of blood cultures.

Microbiological culture methods for pediatric musculoskeletal infection: a guideline for optimal use

BACKGROUND

Culture results affect the diagnosis and treatment of children with musculoskeletal infection. To our knowledge, no previous large-scale study has assessed the relative value of culture methods employed during the evaluation of these conditions. The purpose of this study was to identify an optimal culture strategy for pediatric musculoskeletal infection.

METHODS

Children with musculoskeletal infection were retrospectively studied to assess culture results from the infection site or blood; culture type, including aerobic, anaerobic, fungal, and acid-fast bacteria (AFB); antibiotic exposure history; and clinical history of children with positive culture results.

RESULTS

We studied 869 children, including 353 with osteomyelitis, 199 with septic arthritis, forty-two with pyomyositis, and 275 with abscess. The 4537 cultures processed included 1303 aerobic, 903 anaerobic, 340 fungal, 289 AFB, and 1702 blood. Of 3004 specimens sent during initial work-up, positive results occurred in 677 of 1049 aerobic cultures (64.5%), 140 of 763 blood cultures (18.3%), eighteen of 722 anaerobic cultures (2.5%), five of 251 fungal cultures (2.0%), and two of 219 AFB cultures (0.9%). Staphylococcus aureus was the most common pathogen isolated, from 428 (50.7%) of 844 children for whom blood or infection-site culture material was sent (methicillin-resistant S. aureus, 252; and oxacillin-sensitive S. aureus, 176). Cultures were negative in 206 (29.0%) of the 710 children for whom culture material from the site of infection was sent. Children with true-positive anaerobic, fungal, or AFB cultures had a history of immunocompromise, penetrating inoculation, or failed primary treatment. Antibiotic exposure prior to culture-sample acquisition did not interfere with aerobic culture results from the site of infection.

CONCLUSIONS

Our findings suggest that anaerobic, fungal, and AFB cultures should not be routinely performed during the initial evaluation of children with hematogenous musculoskeletal infection. These cultures should be performed for children with immunocompromise, clinical suspicion of penetrating inoculation, or failed primary treatment.