Reassessment of the incubation time in a controlled clinical comparison of the BacT/Alert aerobic FAN bottle and standard anaerobic bottle used aerobically for the detection of bloodstream infections

Evaluation of Optimal Blood Culture Incubation Time To Maximize Clinically Relevant Results from a Contemporary Blood Culture Instrument and Media System

Timely diagnosis of microorganisms in blood cultures is necessary to optimize therapy. Although blood culture media and systems have evolved for decades, the standard interval for incubation prior to being discarded as negative has remained 5 days. Here, we evaluated the optimal incubation time for the BacT/Alert Virtuo blood culture detection system (bioMérieux) using FA Plus (aerobic) and FN Plus (anaerobic) resin culture bottles in routine clinical use.

Timely diagnosis of microorganisms in blood cultures is necessary to optimize therapy. Although blood culture media and systems have evolved for decades, the standard interval for incubation prior to being discarded as negative has remained 5 days. Here, we evaluated the optimal incubation time for the BacT/Alert Virtuo blood culture detection system (bioMérieux) using FA Plus (aerobic) and FN Plus (anaerobic) resin culture bottles in routine clinical use. Following institutional review board (IRB) approval, a retrospective review evaluated the outcomes of 158,710 bottles collected between November 2018 and October 2019. The number of positive blood bottles was 13,592 (8.6%); 99% of positive aerobic and anaerobic bottles flagged positive by 91.5 and 108 h, respectively. The mean (median) times to positivity were 18.4 h (15.6 h) for Staphylococcus aureus, 12.3 h (9.5 h) for Escherichia coli, 22.2 h (15.9 h) for Pseudomonas aeruginosa, and 48.9 h (42.9 h) for Candida spp. Only 175 bottles (0.1% of all bottles) flagged positive after 4 days of incubation; 89 (51%) of these bottles grew Cutibacterium (Propionibacterium) species. Chart review of blood cultures positive after 4 days (96 h) rarely had a clinical impact and sometimes had a negative impact on patient care. Finally, a seeded study of the HACEK group (i.e., Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, and Kingella), historically associated with delayed blood culture positivity, demonstrated no benefit to extended incubation beyond 4 days. Collectively, these findings demonstrated that a 4-day incubation time was sufficient for the Virtuo system and media. Implementation of the 4-day incubation time could enhance clinically relevant results by reducing recovery of contaminants and finalizing blood cultures 1 day earlier.

Time to blood cultures positivity of microorganisms using a continuous-monitoring automated blood cultures system

Background

Previous studies showed that clinically significant pathogens were detected within 3 days of incubation using a continuous monitoring automated blood culture instrument.

Objectives

To determine time to blood culture positivity (TTP) of microorganisms using a BD BACTEC™ FX.

Methods

A cross-sectional study was conducted at Maharaj Nakorn Chiang Mai Hospital, Thailand from October to November 2014.

Results

One-hundred and eighty-one patients with 195 episodes of infection and 436 cultures were included in the analysis. Among 181 patients, 55.2% were male and the median age was 61 years (interquartile range (IQR) 50, 76). Of the 195 episodes of infections, the most common source was genitourinary tract (15.4%). Overall, the median TTP was 17 hours (IQR 11.5, 24.5), the shortest TTP was observed in Streptococcus agalactiae. Four-hundred and seventy-eight cultures (97.6%) and all (100%) were detected at 3 days and 5 days of incubation. Factors associated with TTP ≤24 hour were blood drawn from patients who had hematologic malignancy (odds ratio (OR) 9.6, 95% confidence interval (CI) 1.2, 74.3, P = 0.030), endocarditis and vascular infection (OR 8.7, 95% CI 1.1, 67.2, P = 0.038), thrombocytopenia (OR 2.4, 95% CI 1.3, 4.4, P = 0.004), clinical of systemic inflammatory response syndrome (SIRS) (OR 2.3, 95% CI 1.2, 4.5, P = 0.014), and not receiving antimicrobials within 72 hours before cultures taken (OR 2.2, 95% CI 1.4, 3.6, P < 0.001).

Conclusions

TTP varied depends upon the pathogens and clinical settings. However, bacteria were isolated from almost, but not all of the blood cultures within 3 days of incubation.

Critical factors in the recovery of pathogenic microorganisms in blood

BACKGROUND

The critical factors for optimal recovery of microbial pathogens from blood are not only the basis for how we perform blood cultures on a daily basis, but are also important for development of all current blood-culture systems. Because much of this research was conducted and published between 1975 and 2010 there is a general sense that many physicians and scientists may not be familiar with it, but it is critical for performing and interpreting blood cultures.

OBJECTIVES

To review the critical factors in the laboratory recovery and isolation of pathogenic microorganisms in blood.

SOURCES

Literature review of published papers, select reviews and updated guidelines.

CONTENT

This review focuses on the critical factors that affect the recovery isolation of pathogenic microorganisms from individuals with bloodstream infections. Contemporary blood-culture systems, and current methods for blood-culture collection, have been designed to incorporate these critical factors so as to optimize recovery and isolation of pathogens while minimizing contamination.

IMPLICATIONS

It is important for microbiologists and practitioners to understand how and why these critical factors affect current blood-culture practices to improve patient management. Future research should emphasize which of these critical factors will still play a role in the era of molecular diagnostic tests, which will no longer be relevant, and which new critical factors have yet to be defined.

Clinical impact of extended blood culture examination: Too much of a good thing

Blood culture is the most critical examination for diagnosing bacterial infections. The longer the blood culture incubation period, the higher the chances of identifying bacterial strains. However, unnecessary extension of the incubation period can burden the capacity of the instrument and merely result in the detection of contaminant bacteria having no clinical significance. This study aimed to optimize the blood culture incubation period using the currently available continuous-monitoring automated blood culture instrument. This was a 2-year retrospective study performed at Osaka University Hospital (January 1, 2016 to December 31, 2017). The BD BACTEC™ FX blood culture system (Becton Dickinson, Sparks, MD, USA) and BD BACTEC™ Plus series blood culture bottles were used. All blood cultures were incubated for more than 12 consecutive days. We reviewed the clinical data of cases that tested positive between 6 and 12 days of incubation. During the study period, 14,822 sets of blood culture were drawn. Of 1751 sets testing positive, 95.7% (1665 sets) became positive within 5 days of incubation. The overall contamination rate (false positives) after 6 days of incubation was 80.2% (69/86 sets). Based on the positive blood culture results, antimicrobials were changed in 7.0% (6/86) of the sets, and a diagnosis of infectious disease was made in only one case. There was no death associated with the extended blood culture results. In conclusion, the clinical impact of extended blood culture incubation for 6 days or more was limited, and a routine extension of the incubation period might be unnecessary.

Major pathogen microorganisms except yeasts can be detected from blood cultures within the first three days of incubation: A two-year study from a University Hospital

The knowledge of the expected time-to-positivity (TTP) of blood cultures by major pathogens is essential both clinically and economically. To this end, we conducted the present two-year study in our Institution, aiming to assess the TTP of all the major microorganisms including Enterobacteriaceae, Pseudomonas aeruginosa, Acinetoacter baumannii, Enterococcii spp, Staphylococcus aureus and yeasts, to determine whether a 3-day interval is sufficient for their detection. The TTP for each case of strain isolation per patient was determined as the TTP of the first bottle among a set of bottles collected within the same period of time to be flagged as positive per patient. Based on our results, almost all major Gram-negative (99.30%), Gram-positive microbia (99.01%) and yeasts (98.85%) were detected within the first 5-days of incubation, leading to the solid conclusion that a 5-day period of incubation is adequate to detect almost all the major routine pathogens. By contrast, when a 3-day period was examined acceptable results were only found for Gram-negative (98.33%) and Gram-positive (98.51%) microbia. A significant proportion of yeasts (8.05%) could not be detected within this time frame. Therefore, regarding the yeasts, a 3-day incubation period cannot be considered as adequate and is not advocated.

Time to Positivity and Antibiotic Sensitivity of Neonatal Blood Cultures

Background:

Sepsis is a commonly encountered and potentially life-threatening problem in neonatal intensive care units, blood culture of neonatal sepsis helps in either optimizing treatment or terminating antibiotics.

Materials and Methods:

We determined the causative agent, time to positivity (TTP), and antibiogram of neonatal blood cultures collected in a tertiary care center, to investigate difference between early- and late-onset neonatal sepsis and to establish the time at which a blood culture could safely be considered negative, using the BacT/ALERT^® 3D 60. A total of 826 clinically suspected neonates suffering from sepsis and admitted to a neonatal intensive care unit of a tertiary care hospital, Alexandria, Egypt were included in this study.

Results:

Eighty-five (10.29%) showed positive results. The overall TTP median was 21.1 h. Out of the 85 positive cultures, 57 (67.06%) were Gram-positive, 15 (17.65%) were Gram-negative, and 13 (15.29%) were fungi (all Candida). Coagulase-negative staphylococci were the predominant organism (41.18%). All the Gram-positive pathogenic isolates were sensitive to vancomycin and tigecycline. Among the Gram-negative isolates, maximum antibiotic sensitivity was observed for levofloxacin.

Conclusion:

We conclude that more than 3 days of incubation may not be required when using the BacT/ALERT^® 3D 60 system.

Comparative evaluation of paired blood culture (aerobic/aerobic) and single blood culture, along with clinical importance in catheter versus peripheral line at a tertiary care hospital

PURPOSE

Paired blood culture (PBC) is uncommon practice in hospitals in India, leading to delayed and inadequate diagnosis. Also contamination remains a critical determinant in hampering the definitive diagnosis.

OBJECTIVES

To establish the need of PBC over single blood culture (SBC) along with the degree of contamination, this comparative retrospective study was initiated.

MATERIALS AND METHODS

We processed 2553 PBC and 4350 SBC in BacT/ALERT 3D (bioMerieux) between October 2010 and June 2011. The positive cultures were identified in VITEK 2 Compact (bioMerieux). True positivity and contaminants were also analyzed in 486 samples received from catheter and peripheral line.

RESULTS

Out of 2553 PBC samples, positivity was seen in 350 (13.70%). In 4350 SBC samples, positivity was seen in 200 samples (4.59%). In PBC true pathogens were 267 (10.45%) and contaminants were 83 (3.25%), whereas in SBC 153 (3.51%) were true positives and contaminants were 47 (1.08%). Most of the blood cultures (99.27 %) grew within 72 h and 95.8% were isolated within 48 h. In 486 PBCs received from catheter/periphery (one each), catheter positivity was found in 85 (true positives were 48, false positives 37). In peripheral samples true positives were 50 and false positives were 8.

CONCLUSION

Significantly higher positive rates were seen in PBCs compared with SBCs. Automated blood culture and identification methods significantly reduced the time required for processing of samples and also facilitated yield of diverse/rare organisms. Blood culture from catheter line had higher false positives than peripheral blood culture. Thus every positive result from a catheter must be correlated with clinical findings and requires further confirmation.

Routine incubation of BacT/ALERT FA and FN blood culture bottles for more than 3 days may not be necessary

We reviewed time to detection for 35,500 blood cultures collected in BacT/ALERT FA and FN bottles. In the first 3 days of incubation, 97.5% of the 2,609 clinically significant isolates were detected, suggesting that routine incubation for more than 3 days may not be necessary for FA and FN bottles.

Surge capacity for response to bioterrorism in hospital clinical microbiology laboratories

Surge capacity is the ability to rapidly mobilize to meet an increased demand. While large amounts of federal funding have been allocated to public health laboratories, little federal funding has been allocated to hospital microbiology laboratories. There are concerns that hospital laboratories may have inadequate surge capacities to deal with a significant bioterrorism incident. A workflow analysis of a clinical microbiology laboratory that serves an urban medical center was performed to identify barriers to surge capacity in the setting of a bioterrorism event and to identify solutions to these problems. Barriers include a national shortage of trained medical technologists, the inability of clinical laboratories to deal with a dramatic increase in the number of blood cultures, a delay while manufacturers increase production of critical products and then transport and deliver these products to clinical laboratories, and a shortage of class II biological safety cabinets. Federal funding could remedy staffing shortages by making the salaries of medical technologists comparable to those of similarly educated health care professionals and by providing financial incentives for students to enroll in clinical laboratory science programs. Blood culture bottles, and possibly continuous-monitoring blood culture instruments, should be added to the national antibiotic stockpile. Federal support must ensure that companies that manufacture essential laboratory supplies are capable of rapidly scaling up production. Hospitals must provide increased numbers of biological safety cabinets and amounts of space dedicated to clinical microbiology laboratories. Laboratories should undertake limited cross-training of technologists, ensure that adequate packaging supplies are available, and be able to move to a 4-day blood culture protocol.

Comparison of recovery of blood culture isolates from two BacT/ALERT FAN aerobic blood culture bottles with recovery from one FAN aerobic bottle and one FAN anaerobic bottle

Traditionally, a routine blood culture for adult patients consisted of paired aerobic and anaerobic bottles, but the routine use of an anaerobic blood culture bottle has been challenged in recent years. In this study, we compared the recovery of two FAN aerobic bottles with one FAN aerobic and one FAN anaerobic bottle. Each pair of bottles was collected by a separate collection procedure, and each bottle held a recommended 8- to 12-ml draw. A total of 704 clinically significant isolates were recovered from 8,620 sets (17,240 pairs), with 487 (69.2%) isolates recovered from one or both bottles in each pair of bottles, 86 isolates (12.2%) recovered only from the FAN aerobic-FAN aerobic pair, and 131 isolates (18.6%) recovered only from the FAN aerobic-FAN anaerobic pair. Significantly more total organisms (P = 0.002), gram-positive cocci (P = 0.03), Staphylococcus aureus (P = 0.05), Enterobacteriaceae other than Escherichia coli (P = 0.02), and anaerobes (P = 0.01) were recovered from the FAN aerobic-FAN anaerobic pair than from the FAN aerobic-FAN aerobic pair. A separate analysis was performed on the 618 isolates that were recovered from the FAN aerobic-FAN anaerobic pair to compare recovery by bottle type. Significantly more S. aureus (P = 0.005) and anaerobes (P < 0.001) were recovered from the FAN anaerobic bottle, while significantly more coagulase-negative staphylococci (P = 0.01), Streptococcus pneumoniae (P = 0.03), and other gram-negative bacilli (P = 0.004) were recovered from the FAN aerobic bottle. These results support the routine use of a FAN anaerobic bottle for use in the culture of blood with the BacT/ALERT system in our institution. These results also suggest that the decision of whether to routinely utilize an anaerobic blood culture bottle should be influenced by the overall recovery of bacteria and yeast, the recovery of specific types of bacteria or yeast, the medium type, and the blood culture system utilized by the laboratory.

Three days of incubation may be sufficient for routine blood cultures with BacT/Alert FAN blood culture bottles

BacT/Alert FAN blood culture bottles have been shown to enhance the recovery of bacteria and yeast from blood compared with standard BacT/Alert bottles. It is well established that standard BacT/Alert blood culture bottles require no more than 5 days of incubation for the detection of routine bacteria and yeast. It is less clear, however, whether FAN bottles also routinely require 5 days of incubation. To address this question, we recently reviewed the results of 17,887 blood culture sets collected in FAN blood culture bottles at Geisinger Medical Center. Of these cultures, 1,780 were positive for bacteria or yeast, yielding a total of 1,242 clinically significant isolates. The numbers of isolates recovered on days 1, 2, 3, 4, and 5 were as follows: (values in parentheses are percentages of total significant isolates): 877 (71%), 269 (22%), 65 (5%), 18 (1%) and, 13 (1%), respectively. In total, 97.5% of all clinically significant isolates were detected in the first 3 days of incubation. Of the 31 significant isolates detected on day 4 or 5 of incubation, 17 were detected in concurrent blood cultures within the first 3 days of incubation. Chart reviews were conducted for the 13 patients with the remaining 14 isolates detected on day 4 or 5 to determine whether therapy was changed due to this blood culture result. Therapy was changed for only 1 patient. These results suggest that it may not be necessary to routinely incubate FAN blood culture bottles for more than 3 days.

Reassessment of the routine anaerobic culture and incubation time in the BacT/Alert FAN blood culture bottles

A total of 9,130 blood cultures were collected from adult patients with suspected bloodstream infections. The recommended 20 mL sample of blood was divided equally between the aerobic and anaerobic FAN bottles and monitored in the BacT/Alert Microbial Detection System for a total of 5 days. There were 757 clinically significant positive culture pairs from 291 patients. Significant differences were found with greater recovery of Pseudomonas aeruginosa (p < 0.001), Acinetobacter spp. (p = 0.002), coagulase-negative staphylococci other than Staphylococcus epidermidis (p = 0.002), and Candida spp. (p < 0.001) from the aerobic bottle and greater recovery of anaerobic bacteria (p < 0.001) from the anaerobic bottle. Significantly more episodes of P. aeruginosa bacteremia (p < 0.003) and candidemia (p < 0.001) were detected by the aerobic FAN bottle and significantly more episodes of anaerobic bacteremia (p < 0.001) were detected by the anaerobic FAN bottle (Table 2). No other significant differences between systems in their detection of bacteremias were noted. Anaerobic bacteremias were encountered in diverse and often unpredictable clinical settings. All clinically significant episodes of bloodstream infection were detected within 4 days of incubation of their cultures. We conclude routine, rather than selective, use of the anaerobic FAN bottle in the blood culture set and a 4-day incubation of blood cultures in the BacT/Alert aerobic and anaerobic FAN bottles is an appropriate routine procedure.