Anaerobic bacteremia: incidence, patient characteristics, and clinical significance

Routine Use of Anaerobic Blood Culture Bottles for Specimens Collected from Adults and Children Enhances Microorganism Recovery and Improves Time to Positivity

The utility of anaerobic blood culture bottles remains controversial, especially for specimens from children. Data are limited on the inclusion of an anaerobic bottle as part of a blood culture "set" when using contemporary blood culture instruments and media. Here, we evaluated the clinical utility of anaerobic blood culture bottles (FN Plus) and aerobic bottles (FA Plus) for the BacT/Alert Virtuo blood culture system (bioMérieux). A total of 158,710 bottles collected between November 2018 and October 2019 were evaluated. There were 6,652 positive anaerobic bottles, of which 384 (5.8%) contained 403 obligate anaerobes. In patients <19 years old, there were 389 positive anaerobic bottles, with 15 (1.8%) containing 16 obligate anaerobes. If not for anaerobic bottles, all but 8 obligate anaerobes would have gone undetected. Furthermore, anaerobic bottles were advantageous for some facultative anaerobes. Staphylococcus aureus from anaerobic bottles demonstrated statistically significant increased recovery (1,992 anaerobic versus 1,901 aerobic bottles, P = 0.009) and faster mean time to positivity (1,138 versus 1,174 min, P = 0.027). Only 25 microorganisms had statistically significant improved recovery and/or faster time to positivity from aerobic versus anaerobic bottles, suggesting anaerobic bottles offer comparable growth for most species. Finally, if only an aerobic bottle had been collected, 2,027 fewer positive cultures would have been detected and 7,452 fewer isolates would have been reported, including cultures with S. aureus (413 isolates, 10.6% less), Pseudomonas aeruginosa (9 isolates, 3.1% less) and Escherichia coli (193 isolates, 14.0% less). Taken together, these findings support the practice of routinely including an anaerobic bottle for blood culture collection.

Identification and distribution of anaerobic bacteria isolated from clinical specimens in a University Hospital: 4 years’ experience

Anaerobes, which are components of microbiota, can cause life-threatening infections. Because of their fastidious nature, they are difficult to isolate and are often overlooked. The goal of this study was to identify the anaerobic bacteria isolated from clinical specimens at the Central Laboratory of Hacettepe University Hospital in 2015-2018 and to evaluate the distribution of the isolated bacterial species among the different specimen types. The anaerobic bacteria isolated from the specimens were identified by the conventional methods and MALDI-TOF MS.

Overall, 15,300 anaerobic cultures were studied. Of these, 14,434 (94.3%) were blood samples and 866 (5.7%) were other clinical specimens. A total of 138 anaerobic bacteria were isolated: 62 (44.9%) were isolated from blood samples and 76 (55.1%) from other specimens. The most isolated anaerobes from blood cultures were Bacteroides spp. (41.9%), followed by Cutibacterium acnes (25.8%) and Clostridium spp. (9.7%). The most isolated anaerobes from the other specimens were Gram-negative bacilli, including Bacteroides spp. (15.8%), Fusobacterium spp. (14.5%), Prevotella spp. (14.5%), and Porphyromonas spp. (2.6%). Anaerobic Finegoldia magna represented the major species among the isolated Gram-positive bacteria (10.5%). Anaerobic growth was observed in 0.4% of all the blood cultures and in 5.8% of the positive blood cultures. The results of our study showed that the incidence of anaerobic bacteremia was stable during the 2015-2018 period.

Detection of Pathogenic Bacteria From Septic Patients Using 16S Ribosomal RNA Gene-Targeted Metagenomic Sequencing

BACKGROUND

Conventional blood cultures were compared to plasma cell-free DNA-based 16S ribosomal RNA (rRNA) gene polymerase chain reaction (PCR)/next-generation sequencing (NGS) for detection and identification of potential pathogens in patients with sepsis.

METHODS

Plasma was prospectively collected from 60 adult patients with sepsis presenting to the Mayo Clinic (Minnesota) Emergency Department from March through August 2019. Results of routine clinical blood cultures were compared to those of 16S rRNA gene NGS.

RESULTS

Nineteen (32%) subjects had positive blood cultures, of which 13 yielded gram-negative bacilli, 5 gram-positive cocci, and 1 both gram-negative bacilli and gram-positive cocci. 16S rRNA gene NGS findings were concordant in 11. For the remaining 8, 16S rRNA gene NGS results yielded discordant detections (n = 5) or were negative (n = 3). Interestingly, Clostridium species were additionally detected by 16S rRNA gene NGS in 3 of the 6 subjects with gastrointestinal sources of gram-negative bacteremia and none of the 3 subjects with urinary sources of gram-negative bacteremia. In the 41 remaining subjects, 16S rRNA gene NGS detected at least 1 potentially pathogenic organism in 17. In 15, the detected microorganism clinically correlated with the patient's syndrome. In 17 subjects with a clinically defined infectious syndrome, neither test was positive; in the remaining 7 subjects, a noninfectious cause of clinical presentation was identified.

CONCLUSIONS

16S rRNA gene NGS may be useful for detecting bacteria in plasma of septic patients. In some cases of gram-negative sepsis, it may be possible to pinpoint a gastrointestinal or urinary source of sepsis based on the profile of bacteria detected in plasma.

Clostridium ramosum rapidly identified by MALDI-TOF MS. A rare gram-variable agent of bacteraemia

Clostridium ramosum is an enteric anaerobic, endospore-forming, gram-positive rod with a low GC content that is rarely associated with disease in humans. We present a case of C. ramosum bacteraemia. To the best of our knowledge, this is the second case of C. ramosum bacteraemia in an elderly patient presenting with fever, abdominal pain and bilious emesis. We highlight the Gram stain variability, the lack of visualization of spores and the atypical morphology of the colonies that showed C. ramosum in a polymicrobial presentation that initially appeared to show monomicrobial bacteraemia. The microorganism was rapidly identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). We present a comprehensive literature review of 32 cases of clinical infections by C. ramosum in which we describe, if available, sex, age, clinical symptoms, predisposing conditions, other organisms present in the blood culture, other samples with C. ramosum , identification methodology, treatment and outcome.

Relevance of anaerobic bacteremia in adult patients: A never-ending story?

Obligate anaerobic bacteria are considered important constituents of the microbiota of humans; in addition, they are also important etiological agents in some focal or invasive infections and bacteremia with a high level of mortality. Conflicting data have accumulated over the last decades regarding the extent in which these pathogens play an intrinsic role in bloodstream infections. Clinical characteristics of anaerobic bloodstream infections do not differ from bacteremia caused by other pathogens, but due to their longer generation time and rigorous growth requirements, it usually takes longer to establish the etiological diagnosis. The introduction of matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS) has represented a technological revolution in microbiological diagnostics, which has allowed for the fast, accurate and reliable identification of anaerobic bacteria at a low sample cost. The purpose of this review article is to summarize the currently available literature data on the prevalence of anaerobic bacteremia in adults for physicians and clinical microbiologists and to shed some light on the complexity of this topic nowadays.

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.

Anaerobic blood culture positivity at a University Hospital in Hungary: A 5-year comparative retrospective study

Anaerobic bacteremia (AB) is usually detected in about 0.5-13% of positive blood cultures. The aim of this study was to determine prevalence of anaerobic bacteremia over a 5-year period (2013-2017), to identify current trends at our University Hospital and to compare the results to those in a similar study (2005-2009) in the same region. During the study period, an average of 23,274 ± 2,756 blood cultures were received per year. Out of the positive blood cultures, 3.3-3.6% (n = 423) yielded anaerobic bacteria, representing 3.5-3.8 anaerobic isolates/1000 blood culture bottles (including both aerobic and anaerobic bottles) per year for hospitalized patients. Mean age of affected patients was 70-73 years (range: 18-102 years) with a male-to-female ratio: 0.60. Most isolated anaerobes were Cutibacterium spp. (54.0 ± 8.5%; n = 247), while among anaerobes other than Cutibacterium spp., Bacteroides and Parabacteroides and Clostridium spp. were the most prevalent. Blood culture time-to-positivity (TTP) for clinically relevant bacteria was 31.4 ± 23.4 h, while for Cutibacterium spp., TTP values were 112.9 ± 37.2 h (p < 0.0001). In conclusion, the prevalence of anaerobic bacteremia should be determined on institutional basis.

Utility of anaerobic bottles for the diagnosis of bloodstream infections

BACKGROUND

Obligate anaerobes usually account for less than 10% of bacteria recovered from blood cultures (BC). The relevance of routine use of the anaerobic bottle is under debate. The aim of this study was to evaluate the utility of anaerobic bottles for the diagnosis of bloodstream infections (BSI).

METHODS

We conducted a 6-month, retrospective, monocentric study in a tertiary hospital. All positive BC were grouped into a single episode of bacteremia when drawn within 7 consecutive days. Bacteremia were classified into contaminants and BSI. Charts of patients with BSI due to obligate anaerobes were studied.

RESULTS

A total of 19,739 blood cultures were collected, 2341 of which (11.9%) were positive. Anaerobic bottles were positive in 1528 (65.3%) of all positive BC but were positive alone (aerobic bottles negative) in 369 (15.8%). Overall 1081 episodes of bacteremia were identified, of which 209 (19.3%) had positive anaerobic bottles alone. The majority 126/209 (60.3%) were contaminants and 83 (39.7%) were BSI. BSI due to facultative anaerobes, obligate aerobes and obligate anaerobes were identified in 67 (80.7%), 3 (3.6%) and 13 (15.7%) of these 83 episodes, respectively. BSI due to obligate anaerobic bacteria were reported in 9 patients with gastro-intestinal disease, in 3 with febrile neutropenia and in 1 burned patient.

CONCLUSIONS

Anaerobic bottles contributed to the diagnosis of a significant number of episodes of bacteremia. Isolated bacteria were mostly contaminants and non-obligate anaerobic pathogens. Rare BSI due to obligate anaerobes were reported mainly in patients with gastro-intestinal disorders and during febrile neutropenia.

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.

Determinants of postoperative morbidity and mortality in children managed for typhoid intestinal perforation in Kano Nigeria

BACKGROUND

Intestinal perforation is a serious but poorly understood complication of typhoid fever. This study aims to determine the patient factors associated with postoperative morbidity and mortality.

METHODS

We retrospectively reviewed the records of all children presenting to our unit with typhoid intestinal perforation (TIP) between March 2009 and December 2013. The patients were grouped based on postoperative outcome status and were compared with respect to patient related variables, using chi square test. Multivariate analysis was performed using a binary logistic regression model. Significance was assigned to a p-value <0.05.

RESULTS

The records of 129 children were analyzed. There were 78 (60.5%) boys and 51 (39.5%) girls. The male/female ratio was 1.53:1. Their ages ranged from 3years to 13years (mean 8.14years; SD 2.61years). A single intestinal perforation was seen in 73.4% (94/128) of them, while 26.6% (34/128) had two or more. Mortality rate was 10.9%. Multivariate analysis showed that multiple intestinal perforations significantly predicted postoperative mortality (p=0.005) and development of postoperative fecal fistula (p=0.013), while serum albumin <32g/L was a predictor of postoperative surgical site infection (p=0.002).

CONCLUSION

Multiple intestinal perforations, a postoperative fecal fistula and hypoalbuminemia adversely affected outcome in our patients.

LEVEL OF EVIDENCE

III (Retrospective study). Type of study-Prognosis study.

Endocarditis caused by anaerobic bacteria

BACKGROUND

Infective endocarditis (IE) caused by anaerobic bacteria is a rare and poorly characterized disease. Most data reported in the literature are from case reports [1-3]. Therefore, we assessed the situation of anaerobic IE (AIE) in Spain using the database of the Spanish Collaboration on Endocarditis (GAMES).

METHODS

We performed a prospective study from 2008 to 2016 in 26 Spanish centers. We included 2491 consecutive cases of definite IE (Duke criteria).

RESULTS

Anaerobic bacteria caused 22 cases (0.9%) of definite IE. Median age was 66 years (IQR, 56-73), and 19 (86.4%) patients were men. Most patients (14 [63.6%]) had prosthetic valve IE and all episodes were left-sided: aortic valves, 12 (54.5%); and mitral valves, 8 (36.4%). The most common pathogens were Propionibacterium acnes (14 [63.6%]), Lactobacillus spp (3 [13.63%]), and Clostridium spp. (2 [9.0%]), and the infection was mainly odontogenic. Fifteen of the 22 patients (68.2%) underwent cardiac surgery. Mortality was 18.2% during admission and 5.5% after 1 year of follow-up. When patients with AIE were compared with the rest of the cohort, we found that although those with AIE had a similar age and Charlson comorbidity index, they were more likely to have community-acquired IE (86.4% vs. 60.9%, p = 0.01), have undergone cardiac surgery (68.2% vs 48.7% p = 0.06), and have had lower mortality rates during admission (18.2% vs. 27.3%).

CONCLUSION

IE due to anaerobic bacteria is an uncommon disease that affects mainly prosthetic valves and frequently requires surgery. Otherwise, there are no major differences between AIE and IE caused by other microorganisms.

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.

Anaerobic bacteraemia: a 10-year retrospective epidemiological survey

In order to identify current trends in anaerobic bacteraemia, a 10-year retrospective study was performed in the University Hospital Brussel, Belgium. All clinically relevant bacteraemia detected from 2004 until 2013 were included. Medical records were reviewed in an attempt to define clinical parameters that might be associated with the occurrence of anaerobic bacteraemia. 437 of the isolated organisms causing anaerobic bacteraemia were thawed, subcultured and reanalyzed using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF). There were an average of 33 cases of anaerobic bacteraemia per year during 2004-2008 compared to an average of 27 cases per year during 2009-2013 (P = 0.017), corresponding to a decrease by 19% between the first and the latter period. Also, the total number of cases of anaerobic bacteraemia per 100,000 patient days decreased from 17.3 in the period from 2004 to 2008 to 13.7 in the period 2009 to 2013 (P = 0.023). Additionally, the mean incidence of anaerobic bacteraemia decreased during the study period (1.27/1000 patients in 2004 vs. 0.94/1000 patients in 2013; P = 0.008). In contrast, the proportion of isolated anaerobic bacteraemia compared to the number of all bacteraemia remained stable at 5%. Bacteroides spp. and Parabacteroides spp. accounted for 47.1% of the anaerobes, followed by 14.4% Clostridium spp., 12.6% non-spore-forming Gram-positive rods, 10.5% anaerobic cocci, 8.2% Prevotella spp. and other Gram-negative rods and 7.1% Fusobacterium spp. The lower gastrointestinal tract (47%) and wound infections (10%) were the two most frequent sources for bacteraemia, with the origin remaining unknown in 62 cases (21%). The overall mortality rate was 14%. Further studies focusing on the antimicrobial susceptibility and demographic background of patients are needed to further objectify the currently observed trends.

Are incidence and epidemiology of anaerobic bacteremia really changing?

Incidence, prognosis and need of performing blood cultures for anaerobic bacteria are under debate, mainly due to the belief that the presence of anaerobes in blood can be easily suspected on clinical basis. We aimed to assess these three points in a retrospective analysis of a 10-year experience in our tertiary hospital. All episodes of significant anaerobic bacteremia diagnosed from 2003 to 2012 were included. Risk factors for mortality and clinical predictability of anaerobic bacteremia were evaluated in 113 randomly selected episodes. Overall incidence of anaerobic bacteremia was 1.2 episodes/1000 admissions, with no significant changes during the 10-year study period. B. fragilis group (38.1 %) and Clostridium spp. (13.7 %) were the most frequent isolated microorganisms. As for the clinical study, 43.4 % of the patients had a comorbidity classified as ultimately fatal or rapidly fatal according to the McCabe and Jackson scale. Clinical manifestations suggestive of anaerobic involvement were present in only 55 % of the patients. Twenty-eight patients (24.8 %) died during the hospitalization. Independent predictive factors of mortality were a high Charlson's comorbidity index and presentation with septic shock, whereas, an adequate source control of the infection was associated with a better outcome. In our centre, incidence of anaerobic bacteremia remained stable during the last decade. The routine use of anaerobic BCs seems to be adequate, since in about half of the cases anaerobes could not be suspected on clinical bases. Moreover, prompt source control of infection is essential in order to reduce mortality of patients with anaerobic bacteremia.

Clostridium ramosum bacteremia: case report and literature review

BACKGROUND

Clostridium ramosum is a common enteric anaerobe but infrequently also a cause of pathologic infection.

METHODS

Case report and literature review.

RESULTS

We reviewed 12 case reports describing infection with C. ramosum. When pathogenic, C. ramosum is cultured most commonly from the inner ear, anaerobic blood samples, or abscesses. Patients with such infections fall into two demographic groups, consisting of young children with ear infections or immunocompromised adults with bacteremia. Resistance of C. ramosum to antibiotics is uncommon.

CONCLUSION

Clostridium ramosum is a common but generally commensal bacterial species. Rarely, it becomes pathogenic in young children or immunosuppressed adults.

Clinical diagnostic accuracy of suspected sources of bacteremia and its effect on mortality

BACKGROUND

Although much has been written about bacteremia, evidence of the clinical diagnostic accuracy of bacteremia sources in the absence of microbiological results and the impact of diagnostic accuracy on mortality is scarce.

METHODS

This is a retrospective study of bacteremia episodes over a 2-year period at a general hospital in Madrid. Congruence analyses between clinically presumed and definite sources, acquisition, causative organism, empirical treatment and progression to death were performed.

RESULTS

The study included 323 bacteremia episodes. Clinicians' diagnostic accuracy was higher for gastrointestinal (88.8%; 95% CI: 79%-84%), respiratory (93.9%; 95% CI: 79%-99%) and urinary tract sources (83.6%; 95% CI: 75%-89%) and lower for skin and soft tissues (77.2%; 95% CI: 54%-92%) and, notably, intravascular sources (56%; 95% CI: 39%-71%). Overall, a non-significant (3.45%; 95% CI: -0.6%-13.5%, p=0.47) increase in mortality was observed in the incorrectly suspected bacteremia source group. Mortality related to a definitive source was significantly higher when an intravascular origin was not suspected, resulting in a 26% increase in mortality (95% CI: 1%-52%, p=0.03). Differences in mortality related to inaccurate source assumptions were non-significant when the definitive bacteremia sources were gastrointestinal, urinary, respiratory, skin and soft tissues or unknown. Mortality in the group receiving appropriate empirical antimicrobial treatment was 10.6% compared with 19.7% mortality in the group receiving inappropriate empirical antimicrobial treatment (OR 2; 95% CI: 1.01-4.25).

CONCLUSIONS

The diagnostic accuracy of bacteremia sources is high in all but intravascular sources. A non-suspected intravascular source and inappropriate empirical treatment are related to a higher mortality.

Population-based assessment of the incidence, risk factors, and outcomes of anaerobic bloodstream infections

BACKGROUND

Anaerobes are a relatively uncommon but important cause of bloodstream infection. However, their epidemiology has not been well defined in non-selected populations. We sought to describe the incidence of, risk factors for, and outcomes associated with anaerobic bacteremia.

METHODS

Population-based surveillance for bacteremia with anaerobic microorganisms was conducted in the Calgary area (population 1.2 million) during the period from 2000 to 2008.

RESULTS

A total of 904 incident cases were identified, for an overall population incidence of 8.7 per 100,000 per year; 231 (26 %) were nosocomial, 300 (33 %) were healthcare-associated community-onset, and 373 (41 %) were community-acquired. Elderly males were at the greatest risk. The most common pathogens identified were: Bacteroides fragilis group (3.6 per 100,000), Clostridium (non-perfringens) spp. (1.1 per 100,000), Peptostreptococcus spp. (0.9 per 100,000), and Clostridium perfringens (0.7 per 100,000). Non-susceptibility to metronidazole was 2 %, to clindamycin 17 %, and to penicillin 42 %. Relative to the general population, risk factors for anaerobic bloodstream infection included: male sex, increasing age, a prior diagnosis of cancer, chronic liver disease, heart disease, diabetes mellitus, stroke, inflammatory bowel disease, human immunodeficiency virus (HIV) infection, chronic obstructive pulmonary disease (COPD), and/or hemodialysis-dependent chronic renal failure (HDCRF). The 30-day mortality was 20 %. Increasing age, nosocomial acquisition, presence of malignancy, and several other co-morbid illnesses were independently associated with an increased risk of death.

CONCLUSION

Anaerobic bloodstream infection is responsible for a significant burden of disease in general populations. The data herein establish the extent to which anaerobes contribute to morbidity and subsequent mortality. This information is key in developing preventative, empiric treatment and research priorities.

Neonatal and maternal postpartum bacteroides bacteremia

OBJECTIVE

A unique case of Bacteroides fragilis bacteremia in a mother and her infant prompted a review of these infections in neonates and postpartum mothers during a five-year period at two institutions in Winnipeg, Manitoba. The purpose was to determine the frequency of these infections and ascertain commonly associated factors.

METHODS

Infants and postpartum mothers diagnosed with bacteroides bacteremia were identified from laboratory records in both hospitals, and their medical charts were retrospectively reviewed.

RESULTS

Bacteroides species were isolated in 10 maternal and four neonatal blood cultures. This represented 8.1% of the positive maternal and 1.2% of the positive neonatal blood cultures obtained during the review. The incidence of maternal infection was 2.56/10,000 deliveries, while that of neonatal infection was 1.03/10,000 live births. Postpartum fever and emergency caesarean section were often noted with maternal postpartum bacteroides bacteremia, while fetal distress, low Apgar scores and respiratory distress were frequent in neonatal bacteremia.

CONCLUSION

Postpartum bacteroides bacteremia should be suspected among women with postpartum fever after emergency caesarean section. However, the occurrence of postpartum fever following emergency caesarian section is not necessarily associated with neonatal bacteroides bacteremia. Neonatal bacteroides bacteremia may not be readily suspected on clinical grounds, so clinicians should ensure that the laboratory procedures routinely used to evaluate neonatal bacteremia at their institutions reliably detect these organisms.

Five-year retrospective epidemiological survey of anaerobic bacteraemia in a university hospital and rewiew of the literature

In spite of the developments in microbiological methods, blood cultures remain the cornerstone for the diagnosis of bacteraemia. Classically, minimum of two bottles are collected on a routine basis: an aerobic bottle, allowing preferential growth of aerobic and facultative anaerobic microorganisms, and an anaerobic bottle, providing suitable environment for strict anaerobic bacteria. Recent reports have documented a decrease in anaerobic bacteraemias and have questioned the need for routine anaerobic blood cultures. Bacteraemia due to anaerobic organisms occurs in 0.5-12% of blood cultures worldwide; however, recent studies from Europe and the USA presented inconsistent data regarding the prevalence of anaerobic bacteraemias between 1993 and 2006. The aims of this retrospective survey were to determine the prevalence of bacteraemias due to anaerobic bacteria and evaluate the importance of anaerobic blood cultures in a university hospital in Szeged, Hungary. We examined the occurrence of bacteraemias due to anaerobic bacteria during a 5-year period, from January 2005 to 2009, in order to identify current trends of anaerobic bacteraemias in our university.

A Critical Appraisal of the Role of the Clinical Microbiology Laboratory in the Diagnosis of Bloodstream Infections

The detection of bloodstream infections is one of the most important functions of clinical microbiology laboratories. Despite advances in blood culture technology and clinical studies that have focused on the detection of bacteremia and fungemia, perfection has not been achieved and uncertainties persist. This review provides perspectives on a number of areas, including the recommended number of blood cultures, duration of incubation of blood cultures, use of anaerobic, in addition to aerobic, blood culture media, value of the lysis-centrifugation method, processing and reporting of probable blood culture contaminants, and limitations of current blood culture methods and systems. We also address the handling of blood cultures in point-of-care locations that lack full microbiology capabilities.

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.

The role of anaerobic bacteria in bacteremia

Anaerobic bacteria remain an important cause of bloodstream infections and account for 1-17% of positive blood cultures. This review summarizes the epidemiology, microbiology, predisposing conditions, and treatment of anaerobic bacteremia (AB) in newborns, children, adults and in patients undergoing dental procedures. The majority of AB are due to Gram-negative bacilli, mostly Bacteroides fragilis group. The other species causing AB include Peptostreptococcus, Clostridium spp., and Fusobacterium spp. Many of these infections are polymicrobial. AB in newborns is associated with prolonged labor, premature rupture of membranes, maternal amnionitis, prematurity, fetal distress, and respiratory difficulty. The predisposing conditions in children include: chronic debilitating disorders such as malignant neoplasm, hematologic abnormalities, immunodeficiencies, chronic renal insufficiency, or decubitus ulcers and carried a poor prognosis. Predisposing factors to AB in adults include malignant neoplasms, hematologic disorders, transplantation of organs, recent gastrointestinal or obstetric gynecologic surgery, intestinal obstruction, diabetes mellitus, post-splenectomy, use of cytotoxic agents or corticosteroids, and an undrained abscess. Early recognition and appropriate treatment of these infections are of great clinical importance.

[Anaerobic bloodstream infections: study of 68 episodes]

INTRODUCTION

There is some controversy regarding the current rates of anaerobic bacteremia. Some authors have described an increasing incidence in recent years, whereas others report declining rates. There is even debate over whether to routinely perform anaerobic blood cultures. We present a prospective analysis of anaerobic bloodstream infections diagnosed at our medical center from January 2003 to May 2008.

RESULTS

Sixty-eight patients had bloodstream infection caused exclusively by anaerobic bacteria. Median age was 64+/-19 years and 63.2% had at least one comorbid condition, including 20.6% with a solid neoplasm, often related to the gastrointestinal tract. The main focus of anaerobic bacteremia was the abdomen (42.6%). The most common isolates were several species from the Bacteroides fragilis group (36.7%), Clostridium spp. (17.6%), Peptostreptococcus spp. (16.1%), and Prevotella spp. (16.1%). Empirical antimicrobial treatment was adequate in 69.1%. Overall mortality was 23.5%, and bacteremia-related mortality was 9.2%. Sepsis, septic shock, and a Pitt score >4 were independent predictors of mortality.

CONCLUSIONS

The incidence of anaerobic bacteremia in our hospital was 0.89 cases per 1000 hospital admissions. Patients at high risk were elderly persons with associated underlying diseases including malignant disease. Mortality was high.

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

BACKGROUND AND OBJECTIVE

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

PATIENTS AND METHOD

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

RESULTS

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

CONCLUSIONS

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

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.

Prognostic factors and impact of antibiotherapy in 117 cases of anaerobic bacteraemia

Bacteraemia due to anaerobic bacteria occurs infrequently, making the systematic use of an anaerobic blood sample bottle in patients with sepsis controversial. We retrospectively reviewed the clinical and microbiological data from all cases of anaerobic bacteraemia in a teaching hospital over 2 years and determined the prognostic factors and antibiotic management. With the goal of evaluating the morbidity and mortality of bacteraemia due to anaerobic bacteria, a case-control study was also performed. One hundred eighty-four blood cultures from 125 patients grew at least one anaerobic bacterium, representing 0.5% of all and 7.0% of the positive blood cultures. One hundred seventeen patients were studied. In 24 cases, anaerobic blood cultures were associated with concomitant aerobic bacteria isolation. The most frequently isolated anaerobic species were Bacteroides sp. (n = 62), Clostridium sp. (n = 25), and Fusobacterium sp. (n = 12). The most frequent site of origin was the digestive tract (n = 61). In 51 cases, patients did not receive adequate empirical antianaerobic therapy. The mortality rate was 27%. Age [odds ratio (OR) 1.059; 95% confidence interval (CI) 1.021-1.100], cancer history (OR 3.21, 95% CI 1.126-9.156), and ineffective definitive antibiotherapy (OR 19.292, 95% CI 5.330-69.832) were independently associated with increased hospital mortality. The 72 patients that could be matched with patients without anaerobic bacteria according to their primary diagnosis had a longer hospitalisation and a trend toward increased mortality (P = 0.08). Anaerobic bacteraemia contributed significantly to the morbidity of the patients, and adequate empirical antibiotherapy may play an important role in the clinical outcomes.

Genotypic diversity of anaerobic isolates from bloodstream infections

Accurate species determination for anaerobes from blood culture bottles has become increasingly important with the reemergence of anaerobic bacteremia and prevalence of multiple-drug-resistant microorganisms. Our knowledge of the taxonomical diversity of anaerobes that cause bloodstream infections is extremely limited, because identification historically has relied on conventional methods. Over a 5-year period, we profiled anaerobic bacteremia at a large tertiary care hospital with 16S rRNA gene sequencing to gain a better understanding of the taxonomical diversity of the bacteria. Of 316 isolates, 16S rRNA gene sequencing and phylogenetic analysis identified 316 (100%) to the genus or taxonomical group level and 289 (91%) to the species level. Conventional methods identified 279 (88%) to the genus level and 208 (66%) to the species level; 75 (24%) were misidentified at the species level, and 33 (10%) results were inconclusive. High intragenus variability was observed for Bacteroides and Clostridium species, and high intraspecies variability was observed for Bacteroides thetaiotaomicron and Fusobacterium nucleatum. Sequence-based identification has potential benefits in comparison to conventional methods, because it more accurately characterizes anaerobes within taxonomically related clusters and thereby may enable better correlation with specific clinical syndromes and antibiotic resistance patterns.

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.

A 62-month retrospective epidemiological survey of anaerobic bacteraemia in a university hospital

The incidence of anaerobic bacteraemia was studied retrospectively over 62 months at Mont-Godinne University Hospital, Yvoir, Belgium. The distribution of organisms, clinical presentations, choice of antimicrobial therapy and clinical outcome were analysed. The proportion of positive blood cultures yielding obligate anaerobes was 3.3%. The overall incidence of clinically significant anaerobic bacteraemia was 0.51 cases/1,000 patient admissions (0.61 cases/10,000 hospital-days), but was significantly higher in patients with active haematological malignancies than in other groups (5.97/10,000 vs. 0.33/10,000 hospital-days; p < 0.05). The Bacteroides fragilis group accounted for 61% of isolates, followed by Clostridium spp. (12.2%), Peptostreptococcus spp. and Leptotrichia spp. (7.3% each) and Fusobacterium spp. (4.8%). The most common risk-factors were gastrointestinal surgery (49%) and active haematological malignancies with chemotherapy and/or bone marrow graft (47%). One or more co-morbidities were present in 30 (77%) of 39 patients. The lower gastrointestinal tract (41%) and the oropharynx (23%) were the two most frequent presumed or proven sources for bacteraemia, with the origin remaining unknown in eight (20.5%) cases. The overall mortality rate (evaluated 7 days after the occurrence of bacteraemia) was 13%. Fatal outcome correlated with the severity of underlying diseases and the immunosuppressed status of the patients rather than with the causative pathogen or the effectiveness of antimicrobial therapy. Likewise, there was no difference in the mortality rate between patients with monomicrobial and polymicrobial bacteraemia. Overall, the data re-emphasise the importance of anaerobic bacteraemia, especially in patients with haematological malignancies.

Decreasing the use of anaerobic culture bottles in selected febrile patients--is it reasonable?

BACKGROUND

Two sets of blood cultures are routinely obtained from febrile patients in the medical wards. The purpose of the present study was to evaluate the distribution of the aerobic versus anaerobic isolates in such patients and to examine the rationale of reducing the number of anaerobic culture bottles in selected patients.

METHODS

A retrospective analysis was performed of all febrile patients admitted to medical wards during 1998. Febrile patients from whom at least two sets of blood cultures were drawn and who had a bacterial isolation in at least one bottle were included.

RESULTS

A total of 317 patients were included in the analysis. Some 98.5% of all isolates were aerobic pathogens. Only 1.5% of all isolates (5/317) included obligatory anaerobes. The rate of isolation in a single anaerobic bottle was 8.5%. Analysis of the available files of patients with a single anaerobic positive bottle demonstrated that an adequate antibacterial agent was administered empirically in most of the cases (93%).

CONCLUSIONS

We conclude that in carefully selected medical patients suspected of having an infectious disease, it is reasonable to obtain one anaerobic and two aerobic bottles rather than two full sets. Such an approach is clinically safe and will cut expenses on culture bottles and laboratory staff work. This approach should be examined in a prospective, randomized study.

Incidence and clinical significance of anaerobic bacteraemia in cancer patients: a 6-year retrospective study

Recent studies have shown that anaerobes account for 0.5-9% of all episodes of bacteraemia in hospitalised patients, with variations according to geographical location and demographic characteristics, most notably age, but few data are available for cancer patients. This study investigated retrospectively the incidence of anaerobic bacteraemia in cancer patients who received non-surgical treatment over a 6-year period at a tertiary oncology centre. Gastrointestinal (27%) and haematological (29%) malignancies were the most common underlying diseases. Among 45 isolates of anaerobic bacteria recovered from 45 patients, Bacteroides spp. and Clostridium spp. were the most frequent pathogens (60% and 22%, respectively). Twenty episodes of bacteraemia were polymicrobial, most frequently with aerobic Gram-negative bacilli (18 cases). The mortality rate for patients with adequate antimicrobial therapy from the outset was 14%, compared with 63% for patients who were not treated adequately at any time.

Clostridium clostridioforme: a mixture of three clinically important species

Clostridium clostridioforme shows much variability in phenotypic and antimicrobial susceptibility tests, suggesting it may be more than a single species even though all strains share unique morphology. This study was designed to determine if there are multiple species and, if so, to demonstrate the differences that exist between them. A total of 107 strains of C. clostridioforme were investigated by sequencing of the 16S rRNA gene, phenotypic studies, and antimicrobial susceptibility testing. In addition, clinical data from patients whose infections yielded an organism identified as C. clostridioforme was reviewed. Data from the above studies revealed three principal species in what has been called C. clostridioforme: Clostridium bolteae, C. clostridioforme, and Clostridium hathewayi. Each species may be distinguished by certain phenotypic tests. All three species were involved in infections, including bacteremia. C. clostridioforme appears to be associated with more serious or invasive human infections than the other two species in the group. Resistance to penicillin G is common and is due to beta-lactamase production. Resistance to clindamycin and moxifloxacin is also seen. The three species differ in terms of virulence and antimicrobial resistance. "C. clostridioforme" actually represents three distinct species that are different in terms of 16S rRNA sequences, phenotypic characteristics, and antimicrobial susceptibility. It is important for microbiology laboratories to distinguish between these species and for clinicians to be aware of the differences between them.

Bacteremia caused by Clostridium intestinale

We describe a case of Clostridium intestinale bacteremia in a previously healthy adolescent female presenting with fever and abdominal pain. The bacterium was definitively identified via 16S rRNA gene sequencing. This is the first report, in the world literature, of human infection caused by this microorganism.

Bacteremia caused by Clostridium symbiosum

We describe a fatal case of Clostridium symbiosum bacteremia in a 70-year-old man with metastatic colon cancer. Our report is the first, in the world literature, of human infection caused by this microorganism.

Diagnosis of infection in sepsis: An evidence-based review

OBJECTIVE

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

DESIGN

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

METHODS

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

CONCLUSIONS

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