Detection of bloodstream infections in children

Group B Streptococcal Neonatal Meningitis

Neonatal bacterial meningitis is a devastating disease, associated with high mortality and neurological disability, in both developed and developing countries. Streptococcus agalactiae, commonly referred to as group B Streptococcus (GBS), remains the most common bacterial cause of meningitis among infants younger than 90 days. Maternal colonization with GBS in the gastrointestinal and/or genitourinary tracts is the primary risk factor for neonatal invasive disease. Despite prophylactic intrapartum antibiotic administration to colonized women and improved neonatal intensive care, the incidence and morbidity associated with GBS meningitis have not declined since the 1970s. Among meningitis survivors, a significant number suffer from complex neurological or neuropsychiatric sequelae, implying that the pathophysiology and pathogenic mechanisms leading to brain injury and devastating outcomes are not yet fully understood. It is imperative to develop new therapeutic and neuroprotective approaches aiming at protecting the developing brain. In this review, we provide updated clinical information regarding the understanding of neonatal GBS meningitis, including epidemiology, diagnosis, management, and human evidence of the disease's underlying mechanisms. Finally, we explore the experimental models used to study GBS meningitis and discuss their clinical and physiologic relevance to the complexities of human disease.

The correct blood volume for paediatric blood cultures: a conundrum?

BACKGROUND

Bloodstream infections (BSIs) are a major cause of morbidity and mortality in paediatric patients. For fast and accurate diagnosis, blood culture (BC) is the reference standard. However, the procedure for blood sampling in paediatric patients, particularly the optimal blood volume, is the subject of controversy stemming from a lack of knowledge of the bacterial load and because of several obstacles such as low intravascular volume and the risk of causing anaemia.

AIMS

The aim of this narrative review is to summarize current knowledge on blood sampling in paediatric patients for BC purposes, in particular blood volume and number and type of BC bottles needed for reasonable future guidelines/recommendations.

SOURCES

A comprehensive literature search of PubMed, including all publications in English, was performed in June 2019 using the search terms 'blood culture', 'blood volume', 'bloodstream infection', 'diagnostic', 'paediatric' and/or 'sepsis'.

CONTENT

The amount of inoculated blood determines the sensitivity, specificity and time to positivity of a BC, and low-level bacteraemia (≤10 cfu/mL) in paediatric patients is presumed to be more common than reported. Current approaches for 'adequate' blood volume for paediatric BC are mainly weight- or age-dependent. Of these recommendations, the scheme devised by Gaur and colleagues seems most appropriate and calls for a sample of 1-1.5 mL for children weighing <11 kg and 7.5 mL for a patient weight of 11-17 kg to be drawn into one BC bottle. Inclusion of a more detailed grading in the weight range 4-14 kg, as published by Gonsalves and colleagues, might be useful.

IMPLICATIONS

This review could be important for future guidelines on paediatric BC collection and thus could contribute to improving patient management and lowering the economic and global health burden associated with BSI. Furthermore, upcoming molecular-based approaches with low sample volumes might be an interesting alternative.

Do we need this blood culture?

OBJECTIVES

This study describes blood culture collection rates, results, and microbiology laboratory charges for 4 leading pediatric inpatient diagnoses (asthma, bronchiolitis, pneumonia, and skin and soft tissue infection [SSTI]) in low-risk patients.

METHODS

This retrospective cohort study was conducted at an urban, academic, quaternary children's hospital. The study period was from January 1, 2011, to December 31, 2011. Inclusion criteria were as follows: 6 months to 18 years of age and primary diagnosis of asthma (International Classification of Diseases, Ninth Revision [ICD-9] codes 493.91-493.92), bronchiolitis (ICD-9 codes 466.11 and 466.19), SSTI (ICD-9 codes 680.00-686.99), or pneumonia (community-acquired pneumonia; ICD-9 codes 481.00-486.00). Patients with complex chronic conditions were excluded. Data were collected via administrative billing data and chart review. Descriptive statistics were performed; χ(2) tests were used for categorical variables, and nonparametric tests were used for continuous variables because of non-normal distributions.

RESULTS

Administrative data review included 5159 encounters, with 1629 (32%) inpatient encounters and 3530 (68%) emergency department/outpatient encounters. Twenty-one percent (n = 343) of inpatient encounters had blood cultures performed, whereas 3% (n = 111) of emergency department/outpatient encounters had blood culture testing performed. Inpatient blood culture utilization varied according to diagnosis: asthma, 4%; bronchiolitis, 15%; pneumonia, 36%; and SSTI, 46%. Charts were reviewed for all 343 inpatients with blood culture testing. Results of all the blood cultures obtained for asthma and bronchiolitis admissions were negative, with 98% and 99% negative or false-positive (contaminant) for SSTI and community-acquired pneumonia, respectively. The approximate financial impact of blood culture utilization (according to gross microbiology laboratory charges) approximated $100 000 over the year for all 4 diagnoses.

CONCLUSIONS

There was a high rate of negative or false-positive blood culture results for these common inpatient diagnoses. In addition, there was a low rate of clinically significant true-positive (pathogenic) culture results. These results identify points of potential blood culture overutilization.

Evaluation of blood culture bottles seeded with X-V factors for the detection of Neisseria meningitidis and Haemophilus influenzae

The purpose of this in vitro study was to determine the ability of seeded and not-seeded commercial pediatric blood culture bottles to support the growth of the most frequently responsible microorganisms for bacterial meningitides (Neisseria meningitidis, and Haemophilus influenzae). Tests have been carried out with an automated colorimetric pediatric blood culture system, BacTAlert, Organon Teknika. Bottles were inoculated with X-V factors and serial dilutions of the each bacterium in six times (10(1)-10(6) colony forming unit [CFU]/ml). The bottles, which were supplemented with X-V factors, proved to be effective and time to detection (TTD) was shorter than the un-seeded bottles (p0.05). Time difference between seeded and not-seeded bottles was getting greater at high dilutions of both bacteria. We consider that in presence of a few bacteria, the seeding of bottles with X-V factors is very critical obtaining N. meningitidis, and H. influenzae as the causative agents of meningitidis. The recovery rate of the microorganisms, which were isolated from cerebrospinal fluid by using the X-V factor-seeded blood culture bottles, is therefore higher than with the conventional culture methods.

Contamination rates of blood cultures obtained by dedicated phlebotomy vs intravenous catheter

CONTEXT

Blood culture is the criterion standard for identifying children with bacteremia. However, elevated false-positive rates are common and are associated with substantial health care costs.

OBJECTIVE

To compare contamination rates in blood culture specimens obtained from separate sites vs through newly inserted intravenous catheters.

DESIGN, SETTING, AND PARTICIPANTS

Observational study conducted January 1998 through December 1999 among patients aged 18 years or younger who were seen at a US children's hospital emergency department and had a blood culture obtained as part of their care. Medical records were reviewed in all cases with a positive blood culture. Patients with indwelling vascular catheters were excluded.

INTERVENTION

All phlebotomy was performed by emergency department registered nurses. During the baseline phase, blood specimens for culture were obtained simultaneously with intravenous catheter insertion. During the postintervention phase, specimens were obtained by a separate, dedicated procedure.

MAIN OUTCOME MEASURE

Contamination rate in the postintervention period compared with the baseline period.

RESULTS

A total of 4108 blood cultures were evaluated, including 2108 during the baseline phase and 2000 in the postintervention phase. The false-positive blood culture rate decreased from 9.1% to 2.8% (P<.001). A statistical process control chart demonstrated a steady-state process in the baseline phase and the establishment of a significantly improved steady state in the postintervention phase. Young age was associated with increased contamination rate in both the baseline and postintervention periods.

CONCLUSION

Blood culture contamination rates were lower when specimens were drawn from a separate site compared with when they were drawn through a newly inserted intravenous catheter.

Bacteraemia complicating severe malaria in children

Bacteraemia associated with severe malaria in childhood is a sporadically reported phenomenon but its incidence and clinical importance are unknown. We have reviewed clinical and laboratory data from 783 Kenyan children sequentially admitted with a primary diagnosis of severe malaria. The overall incidence of bacteraemia in children with severe malaria was 7.8% (95% CI 5.5-10.0); however, in children under 30 months of age the incidence was 12.0% (95% CI 8.3-15.7). The presence of bacteraemia was associated with a 3-fold increase in mortality (33.3% vs. 10.4%, P < 0.001). We conclude that invasive bacterial disease may contribute to the pathophysiology of the clinical syndrome of severe malaria in an important subgroup of children. We recommend that young children with severe malaria be treated with broad-spectrum antibiotics in addition to antimalarial drugs.

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.

Continuous quality improvement for introduction of automated blood culture instrument

Despite the critical nature and high cost of blood cultures, hospitals rely on manufacturers' test site data. As a result, in-hospital testing and compliance evaluation of newly acquired instruments are seldom done. The goal of this study was to apply a continuous quality improvement approach and to develop assessment criteria for all stages from the purchase order, through the on-site instrument evaluation, to the compliance evaluation. Despite the introduction of an automated high-blood-volume instrument (BacT/Alert) in our hospital, 56% of adult patients had only one venipuncture and 89.5% had < or = 20 ml of total blood volume sampled. False positives were associated with overfilling of bottles. These problems occurred because the phlebotomists did not like to perform multiple venipunctures on ill patients; therefore, they were drawing 20 ml of blood from one venipuncture and splitting it between two bottles. Unknown to the staff, the vacuum in the bottles draws significantly more than 10 ml of blood; therefore, the first bottle in the set was frequently overfilled and the second bottle was frequently underfilled. A diagrammatic guideline for a new blood culture protocol based on two venipunctures, taken one immediately after the other, to inoculate three bottles was developed. Compliance evaluation demonstrated that within 1 month of starting the new protocol, 74% of patients had at least two or more venipunctures and 60% had > or = 30 ml of blood drawn per patient episode. This study demonstrates the need for continuous quality improvement, including compliance evaluation, to ensure that the potential benefits of newer blood culture technology are actually realized.

Assessment of gelatin supplementation of PEDS Plus BACTEC blood culture medium

Gelatin supplementation of blood culture media has been shown to neutralize the effects of sodium polyanetholesulfonate and enhance detection of Neisseria species. We evaluated the effect of 1.2% gelatin supplementation of nonradiometric Peds Plus Bactec blood culture medium on the rate and speed of recovery of pathogens from pediatric patients. From June 1991 to June 1992, a total of 6451 paired comparisons of blood cultures in Peds Plus medium and gelatin-supplemented Peds Plus medium were done: 465 organisms were isolated, of which 338 were significant. There were no significant differences in recovery of organisms or the speed of detection of microbial growth between the two media. In particular, the recovery of Neisseria meningitidis (eight isolates) was not improved with gelatin supplementation. In conclusion, gelatin supplementation of Peds Plus Bactec medium does not offer any advantage over the regular Peds Plus Bactec medium.

Comparison of the BacT/Alert pediatric blood culture system, Pedi-BacT, with conventional culture using the 20-milliliter Becton-Dickinson supplemented peptone broth tube

The performance of the Pedi-BacT system, the BacT/Alert (Organon Teknika Corp., Durham, N.C.) pediatric blood culture bottle, was compared with that of a conventional 20-ml supplemented peptone broth tube (Becton-Dickinson Corp., Cockeysville, Md.) (BD system) in matched aerobic cultures. The tubes of the BD system were visually examined daily for 7 days and were subcultured during the first 24 h of incubation. Pedi-BacT cultures were mechanically agitated and continuously monitored for growth by the instrument. Of the 6,628 compliant pairs, 331 (5.0%) were positive in both systems, 220 (3.3%) were positive in the Pedi-BacT system only, and 170 (2.6%) were positive in the BD system only. One (0.02%) false-negative culture and 15 (0.2%) false-positive cultures occurred with the Pedi-BacT system while 20 (0.3%) false-negative cultures and 35 (0.5%) false-positive cultures occurred with the BD system. Of 288 clinically significant organisms detected in matched pairs from which a single isolate was recovered, 176 (61%) were recovered from both systems, 83 (29%) were recovered from the Pedi-BacT system only (P < 0.0001), and 29 (10%) were recovered from the BD system only. Members of the family Enterobacteriaceae (P < 0.01), miscellaneous nonfermenters (P < 0.05), and Candida spp. (P < 0.01) were isolated more frequently in the Pedi-BacT system than in the BD system. No significant difference in recovery of other organisms was found between the systems. The average time to detection for the Pedi-BacT system ranged from 11.5 h for streptococci to 29.7 h for enterococci, while that for the BD system ranged from 20.3 h for streptococci to 66.4 h for some nonfermenters. The BacT/Alert system is a reliable, labor-saving alternative to conventional blood culture methods.

Blood cultures from Bangladeshi children with septicaemia: an evaluation of conventional, lysis-direct plating and lysis-centrifugation methods

The use of a laboratory-made lysis-direct plating and lysis-centrifugation (LDP/LC) device for blood cultivation has been compared with the conventional broth culture method in respect of speed and sensitivity in detecting organism(s) and cost effectiveness. 400 blood cultures yielded 95 clinically significant isolates. Both methods recovered 73 organisms (76.8%); 20 (21%) were detected by LDP/LC methods only, and 2 (2.1%) were isolated by the conventional method only. All the 93 isolates (97.8%) recovered by LDP/LC were isolated within 48 h, whereas the broth culture method took 7 d to isolate a total of 75 organisms (78.9%). The LDP/LC method, with our laboratory-made device, costs one-fourth of the cost of the conventional broth culture system.

Pediatric blood culture evaluation of the BACTEC PEDS Plus and the DuPont Isolator 1.5 systems

A new nonradiometric BACTEC medium has been developed for culturing pediatric blood samples. The BACTEC PEDS Plus medium (BACTEC PED) consists of 20 ml of an enriched broth with resins. In contrast to the other aerobic BACTEC media, there is a lower concentration of sodium polyanetholesulfonate in the medium and more CO2 in the headspace of the vial. This study was conducted in two different pediatric settings to compare the performance of the BACTEC PED medium with the Du Pont Isolator 1.5 system (ISO 1.5) in terms of overall organism recovery and time to detection. Equal volumes of up to 1.5 ml were tested in both systems. A total of 4063 culture sets were analyzed, yielding 301 (7.4%) clinically significant isolates. Of these, 86 (29%) were recovered only from the BACTEC PED and 12 (4%) only from the ISO 1.5 (p less than 0.001). BACTEC PED recovered significantly more staphylococci and Enterobacteriaceae than ISO 1.5 (p less than 0.001 and p less than 0.005, respectively). Detection times of isolates recovered in both systems were comparable. For those patients on antibiotic therapy at the time of culture, 21 (37%) were positive only in the BACTEC PED, whereas two (4%) were positive only in the ISO 1.5. The nontherapy group had 61 (27%) organisms that were detected in BACTEC PED only and 9 (4%) in ISO 1.5 only. These results indicate that BACTEC PED is a significant advance in blood culture systems that will provide a sensitive method for detecting pediatric bacteremias.

Performance of a BACTEC nonradiometric medium for pediatric blood cultures

A BACTEC aerobic nonradiometric medium, PEDS Plus, designed for diagnosis of pediatric bacteremia was evaluated in three hospital centers. Equivalent blood volumes (up to 5 ml) were inoculated into and incubated in BACTEC NR-6A (6A) and PEDS Plus broths. Among 4,581 compliant sets, 289 clinically significant organisms, representing more than 20 bacterial and two Candida species, were isolated. One hundred eighty-one isolates were recovered in both bottles, 75 in PEDS Plus only, and 33 in 6A only (P less than 0.001). Time to detection when both bottles were positive was the same for 129 isolates, detection with PEDS Plus was earlier for 39, and detection with 6A was earlier for 13 (P less than 0.005). Staphylococcus aureus was recovered significantly more often in PEDS Plus than in 6A (P less than 0.01), and more coagulase-negative staphylococci and pediatric pathogens (pneumococci, Haemophilus influenzae, and Streptococcus agalactiae) were recovered in PEDS Plus than in 6A. Coagulase-negative staphylococci and H. influenzae were detected significantly earlier in PEDS Plus (P less than 0.05 and less than 0.01, respectively). When the eight species of the family Enterobacteriaceae isolated were considered together, recovery in PEDS Plus was better than in 6A (P less than 0.05). For 66 of the 143 isolates from patients known to be on antimicrobial therapy at the time blood was drawn, PEDS Plus was superior to 6A. In 45 cases, organisms were isolated from PEDS Plus only (P less than 0.001) and in 21 cases they were isolated from PEDS Plus before 6A (P less than 0.01). PEDS Plus broth aids diagnosis of pediatric bacteremia by increasing recovery of etiologic agents and decreasing the time required for detection.