Anaerobic bacteremia: a retrospective four-year analysis in general medicine and cancer patients

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.

Anaerobic Bacteremia: Impact of Inappropriate Therapy on Mortality

Background

Investigation on incidence and mortality of anaerobic bacteremia (AB) is clinically relevant in spite of its infrequent occurrence and not often explored, which report varies according to period and institutions. Therefore, it is necessary to analyze the incidence and risk factors related to mortality and assess clinical outcomes of AB in current aspect.

Materials and Methods

Characteristics of AB patients and anaerobic bacteria from blood culture at a university hospital in 2012 were reviewed retrospectively. The correlation between risk factors and 28-day patient mortality was analyzed.

Results

A total of 70 non-duplicated anaerobic bacteria were isolated from blood of 70 bacteremia patients in 2012. The history of cardiovascular disease as host's risk factor was statistically significant (P = 0.0344) in univariate and multivariate analysis. Although the inappropriate therapy was not statistically significant in univariate and multivariate analysis, the survival rate of bacteremia was significantly worse in patients who had inappropriate therapy compared with those underwent appropriate therapy (hazard ratio, 5.4; 95% confidence interval, 1.7–6.9; P = 0.004). The most frequently isolated organism was Bacteroides fragilis (32 isolates, 46%), followed by Bacteroides thetaiotaomicron (10, 14%), and non-perfringens Clostridium (7, 10%).

Conclusion

The incidence of AB in 2012 was 2.3% (number of AB patients per 100 positive blood culture patients) and the mortality rate in patients with clinically significant AB was 21.4%. In addition, AB was frequently noted in patients having malignancy and the survival rate of AB was significantly worse in patients who received inappropriate therapy compared with those underwent appropriate therapy.

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.

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.

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.

Clinical features of clostridial bacteremia: a review from a rural area

Blood samples, which were obtained from patients who lived in a rural area with approximately 500 acute-care hospital beds, were cultured from 1990 through 1997. We retrospectively reviewed the blood cultures that yielded Clostridium species (74 [0.12%] of 63,296 cultures). These were obtained from 46 different hospitalized patients (incidents per hospital, 0.03%). The source of the Clostridium species was a gastrointestinal site in 24 patients (52.2%). The most frequently identified Clostridium species was Clostridium perfringens (in 10 [21.7%] of patients), followed by Clostridium septicum (in 9 [19.6%]). Thirty-one patients (67.4%) were aged > or =65 years, 13 patients (28.3%) had diabetes mellitus, and underlying malignancy was present in 22 patients (47.8%). The mortality rate of patients whose condition had been managed surgically was 33%; for those patients whose conditions required medical management, the mortality rate was 58%. Clostridium bacteremia in these patients usually had a gastrointestinal source, it often occurred in patients with serious underlying medical conditions, and it rarely was the result of traumatic farm accidents.

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.