OBJECTIVE: Bacteremia with anaerobic bacteria is generally a marker of severe prognosis. However, population-based data are lacking. Our aim was to describe the epidemiology and the 30-day mortality rate of anaerobic bacteremia in a Danish population-based setting.
METHODS: In this population-based cohort study, all first-time episodes of anaerobic bacteremia from the North Denmark Bacteremia Research Database during 1994-2019 were identified. Information on comorbidities, discharge diagnoses, and mortality was retrieved. 30-day mortality rates were calculated and a multivariate logistic regression analysis to identify risk factors for death was performed.
RESULTS: 1,750 incident episodes with anaerobic bacteremia were identified, corresponding to an incidence of 12.5 per 100,000 inhabitants (increasing from 11.2 in 1994-2014 to 17.7 in 2015-2019). Of these episodes, a third were polymicrobial, and the majority (70%) of patients had one or more comorbid conditions. Abdominal infection was the source of bacteremia in 61% of patients, while it was unknown for 15%. The most frequently isolated genera were Bacteroides (45%), Clostridium (20%) and Fusobacterium (6%). The overall crude 30-day mortality rate was 27%, but rates were even higher for patients of high age, with liver disease, and solid tumors. The odds ratio (OR) for 30-day mortality was 1.32 for Clostridium species, and 1.27 for polymicrobial bacteremia with aerobic bacteria.
CONCLUSIONS: The incidence rate of anaerobic bacteremia increased, and the 30-day mortality rate remained high during the study period. Multiple factors influence on 30-day mortality rates, including high age, liver disease, solid tumor, polymicrobial bacteremia, and bacteremia with Clostridium species.

OBJECTIVE: Bacteroides fragilis is the most frequent cause of anaerobic bacteraemia. Although recent data suggest a rise in antimicrobial resistance (AMR) of this and other anaerobic bacteria, surveillance remains limited due to a lack of both data availability and comparability. However, a newly introduced standardised method for antimicrobial susceptibility testing (AST) of anaerobic bacteria has made larger scale surveillance possible for the first time. The aim of this study was to investigate phenotypic AMR of Bacteroides fragilis isolates from bacteraemia across Europe in 2022.
METHODS: In a multicentre approach, clinical microbiology laboratories in Europe were invited to contribute results of AST for Bacteroides fragilis blood culture isolates (including only the first isolate per patient and year). AST of a selection of four antibiotics was performed locally by participating laboratories in a prospective or retrospective manner, using the new EUCAST disc diffusion method on fastidious anaerobe agar (FAA-HB).
RESULTS: A total of 16 European countries reported antimicrobial susceptibilities in 449 unique isolates of Bacteroides fragilis from blood cultures in 2022. Clindamycin demonstrated the highest resistance rates (20.9%, range 0 - 63.6%), followed by piperacillin-tazobactam (11.1%, 0-54.5%), meropenem (13.4%, 0-45.5%), and metronidazole (1.8%, 0-20.0%), all with wide variation between countries.
CONCLUSIONS: Considering that the mean resistance rates across Europe were higher than expected for three of the four anti-anaerobic antibiotics under surveillance, both local AST of clinically relevant isolates of Bacteroides fragilis and continued surveillance on an international level is warranted.

OBJECTIVE: Despite the importance of abscess lesions in clinical decisions regarding anaerobic bacteremia (AB), their impact on clinical characteristics remains unclear. Herein, we aimed to elucidate the clinical factors associated with AB that were unaccompanied by detectable abscess lesions during the initial phase of infection.
METHODS: This was a multicenter retrospective observational study involving patients with culture-proven AB at six tertiary hospitals in Japan between January 2012 and March 2022. Data on clinical characteristics, laboratory and radiological findings were collected, and their associations with the absence of detectable abscess lesions were analyzed.
RESULTS: In total, 393 participants were included. Abscess lesions were absent in 42.7% of the entire cohort and detectable in the remaining patients. No differences were identified in the malignancy, severity, or 30-day mortality between patients with and without detectable abscess lesions. Multivariate logistic regression analysis adjusted for age and the modified Charlson comorbidity score revealed that the immunosuppressive status (febrile neutropenia or corticosteroid use), C-reactive protein (CRP) level ≤9.8 mg/dL at onset, and the presence of gram-positive anaerobic rods (GPARs) were independently associated with AB unaccompanied by detectable abscess lesions [odds ratios (ORs) 3.24, 3.00, and 2.81, respectively; p < 0.05].
CONCLUSIONS: This study elucidated distinctive clinical and microbiological characteristics of AB unaccompanied by detectable abscess lesions, with relatively lower CRP elevation, immunosuppressive status, and GPARs as the causative anaerobes.

Background and Objectives: Anaerobic bacteria like Fusobacterium can lead to severe and life-threatening infections. The inherent complexities in the isolation of these bacteria may result in diagnostic and therapeutic delays, thereby escalating both morbidity and mortality rates. We aimed to examine data from patients with infections due to Fusobacterium to gain insights into the epidemiology and clinical outcomes of patients with these infections. Methods and Results: We conducted a retrospective analysis of clinical data from a cohort of patients with cultures positive for Fusobacterium species at a tertiary care medical center in the United States. Between 2009 and 2015, we identified 96 patients with cultures positive for Fusobacterium. Patients could be categorized into three groups based on the site of primary infection. Patients with head and neck infections constituted 37% (n 36). Patients with infections of other soft tissue sites accounted for 38.5% (n 37). Patients with anaerobic bacteremia due to Fusobacterium formed 24% (n 23) of the cohort. Surgical intervention coupled with antibiotic therapy emerged as cornerstones of management for patients with head and neck or other soft tissue infections, who generally exhibited more favorable outcomes. Patients with bacteremia were older, more likely to have malignancy, and had a high mortality rate. When speciation was available, Fusobacterium necrophorum was the most frequently isolated species. Conclusions: Our retrospective analysis of epidemiology and clinical outcomes of Fusobacterium infections revealed three distinct cohorts. Patients with head, neck, or soft tissue infections had better outcomes than those with bacteremia. Our findings highlight the importance of employing management strategies based on infection site and underlying comorbidities in patients with Fusobacterium infections. Further research is needed to investigate the optimal therapeutic strategies and identify prognostic indicators to improve clinical outcomes for these complex infections.

UNASSIGNED: Metronidazole treats obligate anaerobic bacterial and protozoal infections, with an elimination half-life of around 8 hours. The long elimination half-life, the favorable ratio of steady-state serum levels to minimum inhibitory concentration, and the presence of active metabolites have led to the consideration of metronidazole use at 12-hour dosage intervals. This systematic review aimed to compare the clinical outcomes of twice-daily and thrice-daily metronidazole dosing.
UNASSIGNED: Using the PRISMA checklist, we searched five databases to systematically identify all relevant studies published up to June 16, 2023.
UNASSIGNED: The final analysis included two published retrospective cohort studies of hospitalized adult patients: a single site study (n = 200) and a multisite study (n = 85) of \"good\" quality, as measured by the Newcastle-Ottawa scale. The reported baseline characteristics of the 8-hour and 12-hour dosing groups were comparable, and neither study identified significant differences in primary and secondary clinical outcomes. Metaanalysis of the need to escalate antibiotic therapy also showed no statistically significant differences using the Mantel-Haenszel fixed-effect method (95% confidence interval: 47.6% lower to 6.4 times higher risk, P = 0.34) and inverse-variance method (risk ratio: 1.87; 95% confidence interval: 0.52-6.65, P = 0.34).
UNASSIGNED: This review suggests that dosing metronidazole every 12 hours is as effective as every-8-hour dosing for hospitalized patients with anaerobic infections. These encouraging findings would benefit from validation by a multicenter randomized controlled trial since there would be many benefits to a 12-hour dosing interval while achieving similar clinical outcomes with traditional dosing. The studies in this systematic review excluded patients with Clostridioides difficile and central nervous system and amebiasis infections, so the findings do not apply to these infection types.

A pediatric patient suffered from renal and hepatic abscesses (through hepatorenal space) and recovered by antibiotics and other therapies. By clinical analysis, the multi-organ abscesses might be caused by bloodstream-disseminated infection. In order to identify the pathogen, we collected kidney biopsy tissue, swabs, and plasma samples, and used metagenomics next-generation sequencing (mNGS) and some traditional methods. The results revealed that polymicrobial especially anaerobic bacteremia (Bacteroides fragilis, et al.) contributed to the abscess formation. What is more, systematic human adenovirus C (HAdV-C) infection was shown, and the virus was isolated. The titer of HAdV-2 neutralizing antibodies was 1/4 in the plasma after symptoms onset. Although the exact mechanism of HAdV-2 infection in multiple abscess formation has not been clarified, the case of multi-organ abscesses in the context of polymicrobial especially anaerobic bacteremia and HAdV infection in healthy children is infrequent.

Despite a low incidence, anaerobic bacteremia remains a serious and often underestimated condition. This retrospective study aims to describe the epidemiology of anaerobic bacteremia and to identify risk factors affecting mortality and the impact of treatment. We included all positive anaerobic blood cultures from January 2018 to December 2019 at the University Hospital of Charleroi (Belgium). We identified 105 episodes of clinically significant anaerobic bacteremia (mean age of patients: 66.4 +/- 16.8 years). The main comorbidities were hypertension, chronic kidney disease, and diabetes. Bacteremia was community-acquired in 70.5% of the episodes. Two thirds of the blood cultures were mono-microbial, and the commonest bacteria found were Bacteroides fragilis group (31.4%), Fusobacterium spp. (17.1%) and Clostridium spp. (15.2%). The main sources of bacteremia were abdominal (35.2%), urinary (17.1%), osteoarticular (14.2%) and pulmonary (12.3%). Surgery within 30 days before hospitalization was more frequent in patients with nosocomial bacteremia (45.2% vs 2.7%, p < 0.0001). An appropriate empirical antibiotic therapy was initiated in 74.7% of patients, and the median duration of antibiotic therapy was 10 [5 - 15] days. One third of patients had a surgical management. Patients who did not survive at day 30 (n = 23 [21.9%]) had significantly lower time to positivity (TTP) values than patients alive at day 30, presented more often with sepsis, had higher Charlson scores and chronic kidney disease, and were more likely to suffer from Clostridium spp. bacteremia. In a Cox proportional hazard analysis, sepsis (OR: 7.32 [95% CI: 2.83- 18.97], p< 0.0001) was identified as an independent risk factors for 30-day mortality, whereas time to positivity ≥ 30 h (OR: 0.24 [95% CI: 0.07 - 0.84], p = 0.025) and an adequate empirical antibiotic therapy (OR: 0.37 [95% CI: 0.15 - 0.94], p = 0.037) were associated with better outcomes. Anaerobic bacteremia has a high mortality rate which justifies the maintenance of empirical antibiotic therapy.

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.

In view of the rising incidence of Anaerobic bacteremia(AB), the use of anaerobic blood culture bottles have been recommended in addition to the aerobic blood culture bottles. The need to perform antimicrobial susceptibility testing(AST) for anaerobes has become mandatory owing to increasing metronidazole resistance. The frequency of AB following large bowel surgery and the metronidazole susceptibility for members of the Bacteroides fragilis group were determined. The incidence of AB was found to be 16%. Seventeen obligate anaerobes were isolated in total, of which B. fragilis was the most common. Two of twelve isolates of B. fragilis were resistant to metronidazole.

This was a multicenter, retrospective study of patients with anaerobic bacteremia comparing metronidazole 500 mg every 8 h versus 500 mg every 12 h. Of 782 patients reviewed, 85 met inclusion criteria. There was no significant difference in mortality, length of stay, or escalation of therapy between dosing strategies.