Clinical assessment of anaerobic isolates from blood cultures

Comparison of clinical characteristics, risk factors, and outcomes of patients infected with Bacteroides fragilis group at a tertiary care hospital in central China between 2017 and March 2024

OBJECTIVES

This study aimed to explore the epidemiology, clinical presentation, and risk factors for treatment failure in patients infected with various Bacteroides fragilis group (BFG) species.

METHODS

We analyzed clinical and laboratory data from 178 patients infected with BFG who were admitted to our hospital between 2017 and 2024. We analyzed categorical data using Chi-square and Fisher exact tests, continuous variables using Student's t-tests or Mann-Whitney U-tests, and risk factors using multivariate logistic regression and Pearson's chi-squared tests.

RESULTS

Bacteroides fragilis (69.7 %) and Bacteroides thetaiotaomicron (16.9 %) were the most prevalent species among 178 BFG isolates. Most patients had polymicrobial infections, with the following pathogens isolated from concurrent samples: Escherichia coli, Klebsiella spp., and Enterococcus spp. Intra-abdominal sites were most frequently infected with BFG. Patients aged >50 years and those who had intravascular catheters were infected with more other Bacteroides species than B. fragilis. Admission to an ICU, respiratory, renal and cardiovascular diseases, and chest drainage were associated more often with B. thetaiotaomicron than with B. fragilis. Gastrointestinal diseases, tracheal intubation, and ICU admission were associated more frequently with treatment failure in patients infected with B. fragilis whereas solid cancers, renal disease, multiple organ dysfunction syndrome, and tracheal intubation were more likely to be associated with treatment failure in patients infected with other Bacteroides spp.

CONCLUSIONS

The most prevalent BFG species in the patients were B. fragilis and B. thetaiotaomicron. The demographic characteristics of the patients, underlying diseases, and risk factors for poor clinical outcomes clearly differed among species.

Rate of severe and fatal infections in a cohort of patients with interstitial lung disease associated with rheumatoid arthritis: a multicenter prospective study

Objective

To describe severe infection, foci of infection, microorganisms, associated factors, and impact on mortality in patients with rheumatoid arthritis-associated interstitial lung disease (RA-ILD).

Patients and methods

The study was based on a multicenter prospective cohort of patients with RA-ILD followed up from 2015 to 2023. The main outcome measures were incident severe infection and fatal infection. We evaluated infectious foci, etiologic agents, vaccination status, variables associated with lung function, and clinical-therapeutic variables in RA. The incidence rate (IR) for infection and mortality was calculated per 100 person-years, and 3 multivariate models were constructed to explore factors associated with infection.

Results

We followed up 148 patients with RA-ILD for a median 56.7 months (699.3 person-years). During this period, 142 patients (96%) had at least 1 infection. A total of 368 infectious episodes were recorded, with an IR of 52.6 per 100 person-years. Of the 48 patients who died, 65% did so from infection. Respiratory infections were the most common first infection (74%), infection overall (74%), and fatal infection (80%) and were caused mostly by SARS CoV-2, Streptococcus pneumoniae, Pseudomonas aeruginosa, and influenza A virus. The factors associated with an increased risk of infection and death in patients with RA-ILD were age, inflammatory activity, and therapy with corticosteroids and immunosuppressants.

Conclusion

Patients with RA-ILD have a high risk of serious infection, especially respiratory infection. Infection develops early, is recurrent, and is frequently fatal. The presence of associated factors such as advanced age, joint inflammation, and treatment highlight the importance of integrated and preventive medical care.

True infection or contamination in patients with positive Cutibacterium blood cultures-a retrospective cohort study

Cutibacterium is a genus often considered a contaminant when present in blood cultures, but it can also cause severe infections, especially related to implanted foreign materials. We investigated the incidence and features of patients with true Cutibacterium infection. Patients with positive Cutibacterium blood cultures between the years 2015-2020 in southern Sweden were identified through microbiology records and medical records were studied retrospectively. Cutibacterium isolates were species determined using MALDI-TOF MS. Patients were classified as having true infection or contamination according to a definition considering both clinical and microbiological features and these groups were compared. A total of 313 episodes of positive Cutibacterium blood cultures were identified in 312 patients. Of these, 49 (16%, corresponding to an incidence of 6 cases per million inhabitants per year) were classified as true infections. The most common species was Cutibacterium acnes (87%), and the majority were elderly men with comorbidities. Patients with true Cutibacterium infection often had an unknown focus of infection (n = 21) or a focus in the respiratory tract (n = 18). We identified one episode of ventriculo-peritoneal shunt infection, three episodes of aortic stent-graft infection, and one episode of infective endocarditis. Two patients, where Cutibacterium was isolated at the site of infection, had only one positive blood culture. The finding of positive Cutibacterium blood cultures should not always be considered contamination. Definitions of true Cutibacterium bacteremia with a demand that more than one blood culture must be positive may miss true infections.

Biographical Feature: Susan E. Sharp, Ph.D., D(ABMM), F(AAM)

"…You have brains in your head. You have feet in your shoes.… You can steer yourself any direction you choose. You're on your own. And you know what you know. And YOU are the [one] who'll decide where to go….

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.

The effect of intervention by an antimicrobial stewardship team on anaerobic bacteremia

The effect of antimicrobial stewardship (AS) on anaerobic bacteremia is uncertain. This study aimed to assess the effect of interventions by the AS team (AST) on clinical and microbiological outcomes and antimicrobial use. An AS program was introduced at Osaka City University Hospital in January 2014; an interdisciplinary AST was established. We enrolled patients with anaerobic bacteremia between January 2009 and December 2018. Patients were classified into the pre-intervention group (from January 2009 to December 2013) and the post-intervention group (from January 2014 to December 2018). A significant decrease in definitive carbapenem use (P = 0.0242) and an increase in empiric tazobactam/piperacillin use (P = 0.0262) were observed in the post-intervention group. The de-escalation rate increased significantly from 9.38% to 32.7% (P = 0.0316) in the post-intervention group. The susceptibility of Bacteroides species and 30-day mortality did not worsen in the post-intervention group. These results showed that interventions by an AST can reduce carbapenem use and increase the de-escalation rate without worsening patient outcomes.

Best Practices of Blood Cultures in Low- and Middle-Income Countries

Bloodstream infections (BSI) have a substantial impact on morbidity and mortality worldwide. Despite scarcity of data from many low- and middle-income countries (LMICs), there is increasing awareness of the importance of BSI in these countries. For example, it is estimated that the global mortality of non-typhoidal Salmonella bloodstream infection in children under 5 already exceeds that of malaria. Reliable and accurate diagnosis of these infections is therefore of utmost importance. Blood cultures are the reference method for diagnosis of BSI. LMICs face many challenges when implementing blood cultures, due to financial, logistical, and infrastructure-related constraints. This review aims to provide an overview of the state-of-the-art of sampling and processing of blood cultures, with emphasis on its use in LMICs. Laboratory processing of blood cultures is relatively straightforward and can be done without the need for expensive and complicated equipment. Automates for incubation and growth monitoring have become the standard in high-income countries (HICs), but they are still too expensive and not sufficiently robust for imminent implementation in most LMICs. Therefore, this review focuses on "manual" methods of blood culture, not involving automated equipment. In manual blood cultures, a bottle consisting of a broth medium supporting bacterial growth is incubated in a normal incubator and inspected daily for signs of growth. The collection of blood for blood culture is a crucial step in the process, as the sensitivity of blood cultures depends on the volume sampled; furthermore, contamination of the blood culture (accidental inoculation of environmental and skin bacteria) can be avoided by appropriate antisepsis. In this review, we give recommendations regarding appropriate blood culture sampling and processing in LMICs. We present feasible methods to detect and speed up growth and discuss some challenges in implementing blood cultures in LMICs, such as the biosafety aspects, supply chain and waste management.

Bacteremia in Systemic Lupus Erythematosus in Patients from a Spanish Registry: Risk Factors, Clinical and Microbiological Characteristics, and Outcomes

OBJECTIVE

To describe the incidence of bacteremia in a large multicentric cohort of patients with systemic lupus erythematosus (SLE) and their clinical characteristics and to identify risk factors.

METHODS

All bacteremic episodes from the Spanish RELESSER registry were included. Clinical and laboratory characteristics concerning bacteremia and SLE status, as well as comorbidities at the time of infection, were retrospectively collected. A comparison with sex- and age-matched SLE controls without bacteremia was made. A logistic regression was conducted.

RESULTS

The study included 114 episodes of bacteremia in 83 patients. The incidence rate was 2.7/1000 patient-years. At the time of bacteremia, the median age was 40.5 (range: 8-90) years, and 88.6% of patients were female. The Safety of Estrogens in Lupus Erythematosus National Assessment-Systemic Lupus Erythematosus Disease Activity Index was 4 [interquartile range (IQR) 8]; 41% had an SLE flare (66% severe); Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index was 3 (IQR 4). A comorbidity was recorded in 64% of cases. At the time of bacteremia, 88.6% received corticosteroids (68.6% > 10 mg/day) and 57% immunosuppressors. Gram-negative bacilli, most frequently Escherichia coli (29.8%), caused 52.6% of the episodes. The bacteremia-related mortality was 14% and bacteremia was recurrent in 27.2% of cases. A dose-response relationship was found between corticosteroids and bacteremia risk. In the multivariate analysis, these factors were associated with bacteremia: elevated creatinine (OR 1.31, 95% CI 1.01-1.70; p = 0.045), diabetes (OR 6.01, 95% CI 2.26-15.95; p < 0.001), cancer (OR 5.32, 95% CI 2.23-12.70; p < 0.001), immunosuppressors (OR 6.35, 95% CI 3.42-11.77; p < 0.001), and damage (OR 1.65, 95% CI 1.31-2.09; p < 0.001).

CONCLUSION

Bacteremia occurred mostly in patients with active SLE and was frequently associated with severe flares and corticosteroid use. Recurrence and mortality were high. Immunosuppressors, comorbidities, and disease-related damage were associated with bacteremia.

Selected Topics in Anaerobic Bacteriology

Alteration in the host microbiome at skin and mucosal surfaces plays a role in the function of the immune system, and may predispose immunocompromised patients to infection. Because obligate anaerobes are the predominant type of bacteria present in humans at skin and mucosal surfaces, immunocompromised patients are at increased risk for serious invasive infection due to anaerobes. Laboratory approaches to the diagnosis of anaerobe infections that occur due to pyogenic, polymicrobial, or toxin-producing organisms are described. The clinical interpretation and limitations of anaerobe recovery from specimens, anaerobe-identification procedures, and antibiotic-susceptibility testing are outlined. Bacteriotherapy following analysis of disruption of the host microbiome has been effective for treatment of refractory or recurrent Clostridium difficile infection, and may become feasible for other conditions in the future.

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.

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.

Detection of bacterial and yeast species with the Bactec 9120 automated system with routine use of aerobic, anaerobic, and fungal media

During the period 2006 and 2007, all blood cultures required by four units at high infective risk and most of those required by other units of the University Hospital of Palermo, Palermo, Italy were performed using a Bactec 9120 automated blood culture system with a complete set of Plus Aerobic/F, Plus Anaerobic/F, and Mycosis IC/F bottles. The aim of the study was to enable the authors to gain firsthand experience of the culture potentialities of the three different media, to obtain information regarding the overall and specific recovery of bacteria and yeasts from blood cultures in the hospital, and to reach a decision as to whether and when to utilize anaerobic and fungal bottles. Although very few bloodstream infections (1.8%) were associated with obligate anaerobes, the traditional routine use of anaerobic bottles was confirmed because of their usefulness, not only in the detection of anaerobes, but also in that of gram-positive cocci and fermentative gram-negative bacilli. In this study, Mycosis IC/F bottles detected 77.4% of all the yeast isolates, 87.0% of yeasts belonging to the species Candida albicans, and 45.7% of nonfermentative gram-negative bacilli resistant to chloramphenicol and tobramycin. In order to improve the diagnosis of fungemia in high-risk patients, the additional routine use of fungal bottles was suggested when, as occurred in the intensive-care unit and in the hematology unit of the University Hospital of Palermo, high percentages of bloodstream infections are associated with yeasts, and/or antibiotic-resistant bacteria and/or multiple bacterial isolates capable of inhibiting yeast growth in aerobic bottles.

Bloodstream infections: evolution and trends in the microbiology workload, incidence, and etiology, 1985-2006

Information available on bloodstream infection (BSI) is usually restricted to short periods of time, certain clinical backgrounds, or specific pathogens, or is just outdated. We conducted the current prospective study of patients with BSI in a 1750-bed teaching hospital to evaluate workload trends and the incidence and etiology of BSI in a general hospital during the last 22 years, including the acquired immunodeficiency syndrome (AIDS) era. The main outcome measures were laboratory workload, trends in incidence per 1000 admissions and per 100,000 population of different microorganisms, and the impact of the human immunodeficiency virus (HIV) epidemic in the period 1985-2006.From 1985 to 2006 we had 27,419 episodes of significant BSI (22,626 patients). BSI incidence evolved from 16.0 episodes to 31.2/1000 admissions showing an annual increase of 0.83 episodes/1000 admissions (95% confidence interval, 0.61-1.05; p < 0.0001). The evolution of the incidence per 1000 admissions and per 100,000 population of different groups of microorganisms was as follows: Gram positives 8.2 to 15.7/1000 admissions and 66.8 to 138.3/100,000 population; Gram negatives 7.8 to 16.2/1000 admissions and 63.5 to 141.9/100,000 population; anaerobes 0.5 to 1.3/1000 admissions and 4.1 to 11.7/100,000 population; and fungi 0.2 to 1.5/1000 admissions and 1.7 to 12.5/100,000 population. All those differences were statistically significant. We observed the emergence of multiresistant Gram-positive and Gram-negative microorganisms. At least 2484 episodes of BSI (9.1%) occurred in 1822 patients infected with HIV. The incidence of BSI in HIV-infected patients increased from 1985 and reached a peak in 1995 (17.6% of BSI). Since 1995, the decrease was continuous, and in 2006 only 3.9% of all BSI episodes occurred in HIV-positive patients in our institution. We conclude that the BSI workload has increased in modern microbiology laboratories. Gram-positive pathogens have overtaken other etiologic agents of BSI. Our observation shows the remarkable escalation of some resistant pathogens, and the rise and relative fall of BSI in patients with HIV.

Reemergence of anaerobic bacteremia

BACKGROUND

During 1974-1988, the incidence of anaerobic bacteremia at the Mayo Clinic (Rochester, MN) decreased. This trend occurred nationally, prompting calls for discontinuation of routine anaerobic blood cultures. However, recently, the sites of anaerobic infection have been shown not to be as predictable as once thought, and since 1993, the incidence of anaerobic bacteremia has increased significantly in our medical center.

METHODS

Records from the Mayo Clinic Division of Clinical Microbiology were used to tabulate the number of cases of anaerobic bacteremia in patients at the clinic for the 12-year period from 1993 through 2004. Medical records for patients with anaerobic bacteremia were reviewed from the periods of 1993-1994 and 2004 to identify differences between these 2 patient populations with different rates of bacteremia.

RESULTS

The mean incidence of anaerobic bacteremias increased from 53 cases per year during 1993-1996 to 75 cases per year during 1997-2000 to 91 cases per year during 2001-2004 (an overall increase of 74%). The total number of cases of anaerobic bacteremia per 100,000 patient-days increased by 74% (P<.001). The number of anaerobic blood cultures per 1000 cultures performed increased by 30% (P=.002). Organisms from the Bacteroides fragilis group, other species of Bacteroides, and Clostridium species were most commonly isolated.

CONCLUSIONS

Anaerobic bacteremia has reemerged as a significant clinical problem. Although there are probably multiple reasons for this change, the increasing number of patients with complex underlying diseases makes the clinical context for anaerobic infections less predictable than it once was. Anaerobic blood cultures should be routinely performed in medical centers with a patient population similar to ours.

Risk factors for mortality in patients with anaerobic bacteremia

Risk factors for mortality in anaerobic bacteremia have been incompletely defined. The aims of the present study were to determine clinical significance by pathogen for a broad range of obligate anaerobic organisms isolated from blood, and to define the factors independently associated with mortality among those with clinically significant bacteremia. All patients who had anaerobic bacteria isolated from blood over a 19-month period (from 1 September 1998 to 1 April 2000) at two urban teaching hospitals were included in this study. Each case was analyzed for clinical significance by means of a retrospective medical record review using predetermined definitions. Information was collected on a broad range of clinical and microbiological factors, which were evaluated for their association with mortality using a Cox proportional hazards model. Among 166 patients with obligate anaerobic bacteria isolated from blood, 73 (44%) were deemed to have clinically significant bacteremia. Clinical significance ranged from 0% (0/53) for Propionibacterium spp. to 96% (43/45) for Bacteroides spp. The crude mortality rate in patients with clinically significant anaerobic bacteremia was 25% (18/73). Mortality was significantly associated with age, polymicrobial infection, and underlying heart, kidney or liver disease in univariate analysis. Only the presence of liver disease (relative risk, 5.3; 95% confidence interval, 1.7-16.0; P=0.003) and patient age (relative risk, 1.06/y; 95% confidence interval, 1.0-1.1; P=0.005) remained significant in multivariate analysis. Among patients with anaerobic bacteremia, clinical significance varies markedly by pathogen and mortality is independently associated with age and underlying liver disease.

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.

Use of simulated blood cultures for time to detection comparison between BacT/ALERT and BACTEC 9240 blood culture systems

In order to avoid the influence of pre-analytical steps, the following study was performed by using sterile blood spiked with defined loads of microorganisms as inoculum. Time-to-Detection (TTD) was evaluated for the most frequently encountered bacteria and fungi in septicemia, comparing two commercially available blood culture systems, BACTEC 9240 (Becton Dickinson) and BacT/ALERT (Organon Teknika). A specific medium, Bactec Mycosis IC/F (Becton Dickinson), was compared with the Bactec Plus Aerobic (Becton Dickinson) and FAN Aerobic (Organon Teknika) media for recovery of fungi in general and in case of mixed bacterial/fungal septicemia. The results show that the BACTEC system detects nearly all enrolled microorganisms significantly faster than the BacT/ALERT; the anaerobic vial contributes to the detection of anaerobes and facultative anaerobes and, in the case of BACTEC, shortens TTD; the Bactec Mycosis IC/F bottle shortens TTD of fungi.

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.

Four-day incubation for detection of bacteremia using the BACTEC 9240

Records of 29,356 blood cultures performed between April 1994 and April 1997, using the BACTEC 9240 continuous monitoring blood culture system, were reviewed retrospectively. From these, 3,127 blood culture vials became positive. Of 95 blood culture isolates detected after three days of incubation, 63 were recovered on day four and 32 on day five. Twenty-six contaminants were recovered on day four, and 21 on day five. Chart review was performed for all day four and five isolates that did not meet our definition of a contaminant. Of the 40 isolates that were clinically insignificant, 31 were recovered on day four, and nine on day five. Of eight clinically significant isolates, six were recovered on day four, and two on day five. Our data support a four-day incubation protocol for the recovery of all clinically significant bacteria with overall sensitivity reduced by only 0.06% when compared with a five-day protocol.

Clinical value of anaerobic blood culture: a retrospective analysis of positive patient episodes

AIM

To investigate the clinical value of anaerobic blood culture.

METHODS

Blood culture bottles (n = 25,185) submitted for culture over a two year period were reviewed.

RESULTS

The bottles yielded 1992 positive patient episodes, a positive rate of 14.4/1000 hospital admissions. Significantly more isolations were obtained from aerobic than from anaerobic bottles. Twelve of the 38 anaerobic episodes were detected in aerobic bottles. Clinical management was influenced in one of 24 patients whose cultures yielded anaerobes from anaerobic bottles only. For a further six patients it was unlikely that the result had any effect on clinical management.

CONCLUSIONS

If aerobic bottles were substituted for the anaerobic bottles, detection of positive patient episodes would increase by at least 6%. A higher yield would be achieved by using two aerobic bottles for routine culture and using anaerobic bottles only for patients where anaerobic culture may influence clinical management.

Effect on organism recovery rate from BacT/Alert blood cultures with reduced incubation period

This retrospective study evaluated 15,377 sets of BacT/Alert blood cultures to determine incubation time for blood cultures. Ninety-six per cent (1476) of total isolates signalled positive within five days and 56 isolates turned positive in five to seven days. Of the 56 organisms recovered between five and seven days, 49 were considered contaminants and seven were considered clinically significant. On assessing the medical records of the patients with the seven clinically significant isolates, it was determined that the clinical outcome would not have changed if these isolates were missed. We conclude that a five day incubation protocol reduces the recovery of skin contaminants while not significantly decreasing the recovery of clinically significant organisms. The data suggest that the incubation time can be further reduced but this policy will depend on the individual institution and their patient population mix.

Advantage of combining resin with lytic BACTEC blood culture media

The BACTEC 9240 (Becton Dickinson, Sparks, Md.) automated blood culture system is based on the continuous monitoring of CO2 production by means of a fluorescent sensor attached to the bottom of a culture vial. We compared two media for this system, resin-containing Plus aerobic/F and Lytic anaerobic/F. Sets of Plus aerobic/F and Lytic anaerobic/F vials inoculated with similar volumes (9 +/- 2.5 ml) were evaluated. In the laboratory, the vials were introduced into the system in accordance with the recommendations of the manufacturer and incubated at 35 degrees C for 5 days. A total of 10,914 sets consisting of two bottles each were obtained from 3,674 patients (2.97 cultures per patient). Of these, 1,233 (11%) were culture positive, including 1,074 (10%) yielding at least one pathogen, and 178 (2%) were contaminated. A total of 1,135 isolates were considered clinically relevant in 624 septic episodes; we isolated 894 from Plus aerobic/F and 852 from Lytic anaerobic/F (P = 0.06 [not significant]). More S. aureus isolates (P = 0.05), Pseudomonas spp. (P < 0.0001), other gram-negative bacteria (P = 0.004), and yeasts (P < 0.0001) were isolated from Plus aerobic/F medium, but more streptococci (P < 0.0001), E. coli (P = 0.02) strains and anaerobes (P < 0.0001) were detected with Lytic anaerobic/F medium. Lytic anaerobic/F vials were significantly (P < 0.0001) more often positive at least 6 h before Plus aerobic/F vials (n = 112 versus 52, respectively). Significantly more (P < 0.0001) Plus aerobic/F vials (n = 210; 1.9%) than Lytic anaerobic/F vials (n = 42; 0.4%) were unconfirmed positives. Plus aerobic/F and Lytic anaerobic/F proved to be a valuable pair of blood culture media. Plus aerobic/F performs better for patients under antibiotic treatment, due to the antimicrobial-neutralizing effect of resins. For patients without antibiotic therapy, more microorganisms could be isolated from Lytic anaerobic/F due to cell lysis.

Update on detection of bacteremia and fungemia

The presence of microorganisms in a patient's blood is a critical determinant of the severity of the patient's illness. Equally important, the laboratory isolation and identification of a microorganism present in blood determine the etiologic agent of infection, especially when the site of infection is localized and difficult to access. This review addresses the pathophysiology and clinical characteristics of bacteremia, fungemia, and sepsis; diagnostic strategies and critical factors in the detection of positive blood cultures; characteristics of manual and instrument approaches to bacteremia detection; approaches for isolating specific microorganisms associated with positive blood cultures; and rapid methods for the identification of microorganisms in blood cultures.

Utilization and diagnostic yield of blood cultures in a surgical intensive care unit

OBJECTIVE

To evaluate the diagnostic yield of blood cultures obtained in a surgical intensive care unit (ICU) and to assess factors potentially influencing yield.

DESIGN

Retrospective, descriptive study.

SETTING

Surgical ICU in a university hospital.

SUBJECTS

All patients who had a blood culture obtained during their admission to the trauma/neurosurgical ICU of Presbyterian University Hospital from January 1, 1993 to December 31, 1993.

MEASUREMENTS AND MAIN RESULTS

Blood culture isolates were categorized as pathogens or contaminants and overall diagnostic yield was determined. Blood cultures were positive for pathogens in 4.6% of all culture episodes, while contaminants were isolated in 5.5% of all culture episodes. A total of 23 true bacteremias were identified in 21 patients, for an overall rate of bacteremia of 3.6 per 100 admissions (5.9 per 1,000 patient days). Concurrent antibiotics were being used at the time of blood culture in 65.3% of all culture episodes. The yield for pathogens was significantly lower (2.2%) when cultures were obtained on antibiotics compared with culture episodes obtained off antibiotics (6.4%) (p < .05). Single-set blood culture episodes were obtained in approximately 32% of all culturing episodes with the overall yield for pathogens of these culturing episodes lower (2.9%) than that of multiple-set culture episodes (5.3%) (p = NS).

CONCLUSIONS

Blood culture yield in this surgical ICU was relatively low in comparison with other published studies. The data further suggest that concurrent use of systemic antibiotics and inappropriate or excessive culturing may negatively influence blood culture yield.

Controlled clinical laboratory comparison of BACTEC plus aerobic/F resin medium with BacT/Alert aerobic FAN medium for detection of bacteremia and fungemia

Blood specimens collected from adult patients with suspected sepsis in four medical centers were inoculated into BACTEC Plus/F and BacT/Alert FAN aerobic culture bottles. Both bottles of 7,401 bottle pairs contained the prescribed blood volume of 8 to 12 ml. Bottles were incubated in their respective instruments for a standard 7-day protocol or until the instruments signaled that they were positive. A total of 720 isolates that were judged to represent true infections were recovered from 338 patients; 451 isolates were recovered from both bottles, 143 were recovered from only the Plus/F bottle, and 126 were recovered from only the FAN bottle (P was not significant). Although more Histoplasma capsulatum isolates were recovered from Plus/F bottles (P < 0.005), there were no other statistically significant differences in recovery rates of individual species or groups of organisms between the two systems. Of 329 monomicrobic patient septic episodes, 244 episodes were detected by both blood culture systems, 40 were detected only by the BACTEC system, and 45 were detected only by the BacT/Alert system (P was not significant). There was no significant difference between the two systems in the detection of septic episodes among patients receiving antibiotic therapy at the time of blood cultures. Of the cultures found to be positive within the first 72 h of incubation, detection was on average earlier by the BACTEC system (16.9 h) than by the BacT/Alert system (18.7 h). Larger differences in average time to detection were seen with streptococci (10.7 h by the BACTEC system and 17.9 h by the BacT/Alert system) and yeasts (an average of 29.4 h by the BacT/Alert system versus 37.2 h by the BACTEC system). With the exception of the differences noted above, BACTEC Plus/F aerobic resin and BacT/Alert aerobic FAN blood culture bottles were comparable in their abilities to recover aerobic and facultative organisms.

Clinical comparison of the BACTEC 9000 Standard Anaerobic/F and Lytic/F blood culture media

An 8-month prospective, volume controlled, comparison of Standard Anaerobic/F media with a new anaerobic high blood volume lytic medium (Lytic/F) was performed. A total of 2,092 compliant sets, consisting of an aerobic resin bottle or standard aerobic bottle, Standard Anaerobic/F, and Lytic/F bottle were evaluated. A total of 220 (10.6%) positive specimens were detected from the paired anaerobic bottles. These consisted of 194 true positive and 26 false positive bottles. Of 207 total organisms isolated, 122 were considered clinically significant. A comparison of significant organism recovery revealed 79 isolates in both anaerobic bottles, 7 isolates in the standard Anaerobic/F bottle only, and 36 isolates in the Lytic/F bottle only (p < 0.001). The lytic/F bottle detected significantly more Enterobacteriaceae (p < 0.005) and Streptococci (p < 0.05). There were 24 false positive Standard Anaerobic/F bottles and 2 false positive Lytic/F bottles (p < 0.001). When both bottles were positive the Standard Anaerobic/F bottle was positive 12 hours earlier in 1 instance whereas the Lytic/F bottle was positive 12 hours earlier in 8 instances. The mean time for detection in the Standard Anaerobic/F bottle was 18.2 hours versus 13.2 hours for the Lytic/F bottle. The new Lytic/F anaerobic blood culture media was found to be superior to Standard Anaerobic/F media for both total organism recovery and time to organism detection.

Clinical comparison of isolator and thiol broth with ESP aerobic and anaerobic bottles for recovery of pathogens from blood

The recovery of pathogens and the speed of their detection were determined for our conventional blood culture system (an Isolator [Wampole] and a 100-ml Thiol bottle [Difco]) compared with automated ESP aerobic and anaerobic bottles (80 ml each; Difco). Each of the four culture devices was inoculated with approximately 10 ml of blood from symptomatic patients weighing more than 80 lb (ca. 36 kg). From 7,070 sets of cultures for 2,841 patients, 607 clinically significant isolates were recovered: 456 (75.1%) from the Isolator, 353 (58.2%) from Thiol, 377 (62.1%) from ESP aerobic bottles, and 346 (57.0%) from ESP anaerobic bottles. Of the 607 isolates, 149 (24.5%) were detected only with the conventional system (Isolator and/or Thiol), and 65 (10.7%) were detected only with the ESP two-bottle system (P < 0.001). Our conventional system allowed for detection of significantly more isolates of members of the family Enterobacteriaceae (P < 0.001), Staphylococcus aureus (P < 0.01), Staphylococcus spp. (coagulase-negative) (P < 0.01), and Enterococcus spp. (P < 0.05), and ESP facilitated detection of significantly more isolates of S. pneumoniae (P < 0.01). When all four devices in a culture set were positive for the same isolate, no microbial species or group was detected significantly earlier ( > or = 24 h) by either blood culture system. The Isolator contamination rate (4.8%) was > or = 6 times the rate for any of the bottles. Of pathogens detected by the Isolator, 50% were recovered in counts of < or = 1.0 CFU/ml and 18% were recovered only as a single colony. The ESP system offered an automated, less labor-intensive blood culture system for which routine subcultures were not required, but the important considerations of culturing large volumes of blood and of obtaining at least two sets from each patient in our population were reemphasized.