Timing of specimen collection for blood cultures from febrile patients with bacteremia

Bloodstream infections are an important cause of morbidity and mortality. Physician orders for blood cultures often specify that blood specimens be collected at or around the time of a temperature elevation, presumably as a means of enhancing the likelihood of detecting significant bacteremia. In a multicenter study, which utilized retrospective patient chart reviews as a means of collecting data, we evaluated the timing of blood culture collection in relation to temperature elevations in 1,436 patients with bacteremia and fungemia. The likelihood of documenting bloodstream infections was not significantly enhanced by collecting blood specimens for culture at the time that patients experienced temperature spikes. A subset analysis based on patient age, gender, white blood cell count and specific cause of bacteremia generally also failed to reveal any associations.     

Clinical implications of positive blood cultures.

Positive blood cultures can be classified according to their veracity (true-positive or false-positive culture), clinical severity (inconsequential or life threatening), place of origin (community acquired or nosocomial), source (primary or secondary), duration (transient, intermittent, or continuous), pattern of occurrence (single episode, persistent, or recurrent), or intensity (high or low grade). In general, however, positive blood cultures identify a patient population at high risk of death. In my studies, patients with positive blood cultures were 12 times more likely to die during hospitalization than patients without positive blood cultures. Many bacteremias and fungemias occur in complicated clinical settings, and it appears that only about one-half of the deaths among affected patients are due directly to infection. Hence, it is appropriate to speak of "crude mortality" and "attributable mortality." Among hospitalized patients, recent trends include rising incidences of Staphylococcus aureus and coagulase-negative staphylococcal and enterococcal bacteremias and a dramatic increase in the incidence of fungemias. The diagnostic and therapeutic implications of blood cultures positive for specific microorganisms continue to evolve and are the subject of a large and growing medical literature.     

Comparisons of clinical features and outcomes between Elizabethkingia meningoseptica and other glucose non-fermenting Gram-negative bacilli bacteremia in adult ICU patients

BackgroundClinical information of Elizabethkingia meningoseptica (EM) bacteremia in intensive care unit (ICU) patients is limited and the impact on outcomes uncertain. The aim of this study was to investigate the clinical features and impact of EM bacteremia compared to other glucose non-fermenting Gram-negative bacilli (GNF-GNB) bacteremia in ICU patients.MethodsThis retrospective cohort study enrolled 70 patients who developed GNF-GNB bacteremia after ICU admission, including 19 cases of EM bacteremia (19/70, 27.1%). The main outcome measure was in-hospital mortality.ResultsThe patients with EM bacteremia had a lower rate of appropriate antibiotic therapy (15.8% vs. 62.7%, p < 0.001) and a longer time to appropriate antibiotic therapy (76.8 ± 46.4 vs. 35.1 ± 38.7 h, p < 0.001), but with a less severity in acute physiology and chronic health evaluation (APACHE) II score and shock status (p < 0.05) at the onset of bacteremia, compared to those with non-EM bacteremia. The in-hospital mortality between those with EM bacteremia and non-EM bacteremia was similar (63.2% vs. 51.0%, p = 0.363). However, primary bacteremia was more frequently noted in EM compared with non-EM group (57.9% vs. 25.5%, p = 0.011), and odds ratio 4.294 (95% confidence interval 1.292–14.277, p = 0.017) in multivariate regression analysis.ConclusionAmong the patients with GNF-GNB bacteremia, the numbers of the cases with primary bacteremia and inappropriate therapy were significantly more in EM group than those in non-EM group.     

Predominance of Gram-negative bacilli among patients with catheter-related bloodstream infections

We evaluated changes in the epidemiology of catheter-related bloodstream infections (CRBSIs) between 1996 and 2012 in a tertiary care centre in Israel. The cohort included 1754 episodes of CRBSI. The incidence of CRBSIs decreased throughout the study period, whereas 30-day mortality following bacteraemia increased. There was a linear shift toward predominance of Gram-negative bacilli throughout the study period (p for trend <0.001). In 1996, 68% (68/100) of CRBSIs were caused by Gram-positive cocci, whereas in 2012 77.8% (28/26) were caused by Gram-negative bacilli. The shift towards Gram-negative CRBSIs and the associated mortality mandates that empirical treatment for CRBSIs be directed by local epidemiology.     

Time to positivity of follow-up blood cultures in patients with persistent Staphylococcus aureus bacteremia

We investigated the clinical usefulness of time to blood culture positivity (TTP) of follow-up positive blood cultures (FUPBC) in patients with persistent Staphylococcus aureus bacteremia (SAB). Of the patients who did not have resolution of SAB after primary therapeutic intervention (PTI), patients who had decreases in TTP of FUPBC after PTI more frequently experienced 30-day mortality or secondary foci of infection than those who did not have decrease in TTP (83.3% vs. 28.6%; p?=?0.005).     

Positive follow-up blood cultures identify high mortality risk among patients with Gram-negative bacteraemia

ObjectivesThe role of follow-up blood cultures (FUBCs) in the management of Gram-negative bacteraemia (GNB) is poorly understood. We aimed to determine the utility of FUBCs in identifying patients with increased mortality risk.MethodsAn observational study with a prospectively enrolled cohort of adult inpatients with GNB was conducted at Duke University Health System from 2002 to 2015. FUBCs were defined as blood cultures performed from 24 hours to 7 days from initial positive blood culture.ResultsAmong 1702 patients with GNB, 1164 (68%) had FUBCs performed. When performed, FUBCs were positive in 20% (228/1113) of cases. FUBC acquisition was associated with lower all-cause in-hospital mortality (108/538, 20%, vs. 176/1164, 15%; p 0.01) and attributable in-hospital mortality (78/538, 15%, vs. 98/1164, 8%; p < 0.0001). Propensity score–weighted Cox proportional hazards models revealed that obtaining FUBCs was associated with reductions in all-cause (hazard ratio (HR) 0.629; 95% confidence interval (CI), 0.511–0.772; p < 0.0001) and attributable mortality (HR 0.628; 95% CI, 0.480–0.820; p 0.0007). Positive FUBCs were associated with increased all-cause mortality (49/228, 21%, vs. 110/885, 11%; p 0.0005) and attributable mortality (27/228, 12%, vs. 61/885, 7%; p 0.01) relative to negative FUBCs. Propensity score–weighted Cox proportional hazards models revealed that positive FUBCs were associated with increased all-cause (HR 2.099; 95% CI, 1.567–2.811; p < 0.0001) and attributable mortality (HR 1.800; 95% CI, 1.245–2.603; p 0.002). In a calibration analysis, a scoring system accurately identified patients at high risk of positive FUBCs.ConclusionsRates of positive FUBCs were high and identified patients at increased risk for mortality. Clinical variables can identify patients at high risk for positive FUBCs. FUBCs should be considered in the management of GNB.     

Validity of earlier positivity of central venous blood cultures in comparison with peripheral blood cultures for diagnosing catheter-related bacteremia in cancer patients

We carried out a prospective study in two French Comprehensive Cancer Centers (95 and 184 beds, respectively) to assess the validity of a test based on the earlier positivity of central venous blood cultures in comparison with peripheral blood cultures for predicting catheter-related bacteremia. The differences between the times to positivity for the 21 patients with clinical catheter-related bacteremia and the differences between the times to positivity for the nine patients with bacteremia due to another source were compared by the median test. The difference between the median values was significant (P = 0.0003). A receiver operating characteristic curve was constructed to determine the optimum threshold of the test, which appeared to be at the cutoff point of >/=+3 h, with 100% specificity and 81% sensitivity. The positive and negative predictive values obtained with this cutoff point confirmed the efficacy of the test for predicting the presence or absence of catheter-related bacteremia in cancer patients. The cutoff point was then used to post-classify the 68 episodes of bacteremia from an unknown source. The characteristics and clinical course of both the positive and negative post-classified episodes did not show that the test was clearly useful for a large number of clinical presentations. We therefore suggest restricting it to febrile neutropenic cancer patients for whom clinical signs of infection are slight or absent and when the test is positive.     

Factors associated with positive blood cultures in outpatients with suspected bacteremia

Blood cultures are routinely taken in outpatients with fever and suspected bacterial infections. However, in the majority of cases, they are not informative and of limited value for clinical decision making. The aim of this study was therefore to investigate factors associated with positive blood cultures in outpatients presenting to an outpatient clinic and emergency room. This was a case–control study of all outpatients with positive blood cultures from January 1, 2006 to October 31, 2007 and matched control patients with negative blood cultures in the same time period. Microbiology results and medical charts were reviewed to determine factors associated with positive blood cultures. The presence of a systemic inflammation response syndrome (SIRS) (OR 2.7, 95% Cl 1.0–7.2) and increased C-reactive protein (CRP) (OR 1.1 per 10 mg/l, 95% Cl 1.0–1.2) were the most powerful predictive values for the development of positive blood cultures. In positive cases serum albumin was lower (35 mg/l versus 39 mg/l) than in controls. SIRS, increasing CRP and low albumin were associated with positive blood cultures in outpatients. With simple clinical assessment and few laboratory tests indicative of infection, it is possible to define a group at higher risk for bacteremia in outpatients.     

Rapid identification of gram-negative bacilli from blood cultures

Blood-culture broths showing macroscopic or radiometric evidence of growth of gram-negative bacilli were examined by a rapid automated bacterial identification system. A differential centrifugation technique was developed to prepare suitable inocula. The identification results obtained were confirmed by the API 20E method, with single colonies of the strains isolated 24 h later. Of 90 organisms tested, seven did not give the same identification by the two systems. With the rapid automated technique a presumptive identification of gram-negative bacilli can be made 24 h earlier than by more conventional methods.     

Microbial and clinical determinants of time-to-positivity in patients with bacteraemia

Time-to-positivity is useful in the diagnosis of catheter-related bacteraemia and as a predictor of an endovascular source in patients with Staphylococcus aureus bacteraemia. However, this parameter has been evaluated for only a limited number of microorganisms. In the present study, time-to-positivity was recorded for 1872 episodes of significant monomicrobial bacteraemia diagnosed at a teaching hospital during a 2-year period, and the associated microbial and clinical variables were investigated. According to multivariate analysis, Streptococcus pneumoniae , β-haemolytic streptococci, Escherichia coli , Klebsiella , Enterobacter , Citrobacte r and Aeromonas were characterised by fast growth, with an endovascular source, shock, liver cirrhosis and neutropenia also predicting a short time-to-positivity. For patients not receiving appropriate antibiotics, detection of Gram-positive cocci in clusters within 14 h was predictive of Staph. aureus ; a time-to-positivity of >21 h ruled out the possibility that a Gram-positive organism in chains was a β-haemolytic streptococcus or Strep. pneumoniae , and a time-to-positivity of ≤12 h meant that it was very unlikely that a Gram-negative bacillus was a non-fermenter. A time-to-positivity of ≤8 h was predictive of a non-urinary tract source in patients with E. coli bacteraemia, and detection of growth within 13 h predicted an endovascular source in those with Staph. aureus bacteraemia. In conclusion, time-to-positivity depended on the microorganism, original source and clinical variables involved. Although this measurement may provide some early clues concerning the microorganisms involved and the source of bacteraemia, its clinical impact remains to be defined.     

Current time-to-positivity of blood cultures in febrile neutropenia: a tool to be used in stewardship de-escalation strategies

Objectives

We aimed to describe the current time-to-positivity (TTP) of blood cultures in individuals with onco-haematological diseases with febrile neutropenia. We assessed the probability of having a multidrug-resistant Gram-negative bacilli (MDR-GNB) bloodstream infection (BSI) 24 h after cultures were taken, to use this information for antibiotic de-escalation strategies.

Bacteremic complications of intravascular catheter tip colonization with Gram-negative micro-organisms in patients without preceding bacteremia

Although Gram-negative micro-organisms are frequently associated with catheter-related bloodstream infections, the prognostic value and clinical implication of a positive catheter tip culture with Gram-negative micro-organisms without preceding bacteremia remains unclear. We determined the outcomes of patients with intravascular catheters colonized with these micro-organisms, without preceding positive blood cultures, and identified risk factors for the development of subsequent Gram-negative bacteremia. All patients with positive intravascular catheter tip cultures with Gram-negative micro-organisms at the University Medical Center, Utrecht, The Netherlands, between 2005 and 2009, were retrospectively studied. Patients with Gram-negative bacteremia within 48 h before catheter removal were excluded. The main outcome measure was bacteremia with Gram-negative micro-organisms. Other endpoints were length of the hospital stay, in-hospital mortality, secondary complications of Gram-negative bacteremia, and duration of intensive care admission. A total of 280 catheters from 248 patients were colonized with Gram-negative micro-organisms. Sixty-seven cases were excluded because of preceding positive blood cultures, leaving 213 catheter tips from 181 patients for analysis. In 40 (19%) cases, subsequent Gram-negative bacteremia developed. In multivariate analysis, arterial catheters were independently associated with subsequent Gram-negative bacteremia (odds ratio [OR] = 5.00, 95% confidence interval [CI]: 1.20–20.92), as was selective decontamination of the digestive tract (SDD) (OR = 2.47, 95% CI: 1.07–5.69). Gram-negative bacteremia in patients who received SDD was predominantly caused by cefotaxime (part of the SDD)-resistant organisms. Mortality was significantly higher in the group with subsequent Gram-negative bacteremia (35% versus 20%, OR = 2.12, 95% CI: 1.00–4.49). Patients with a catheter tip colonized with Gram-negative micro-organisms had a high chance of subsequent Gram-negative bacteremia from any cause. This may be clinically relevant, as starting antibiotic treatment pre-emptively in high-risk patients with Gram-negative micro-organisms cultured from arterial intravenous catheters may be beneficial.     

Automated screening of blood cultures with the Malthus microbiological growth analyser.

A total of 3347 blood cultures from patients in all hospital wards were examined on a Malthus microbiological growth analyser and by a conventional system. There was no significant difference in the total numbers of positive cultures of clinical importance between the two systems (p greater than 0.05). Staphylococcus aureus, however, was isolated more often by the conventional method (p less than 0.05). Failure of the automatic detection routine limited the potential of the Malthus system for earlier detection of positive cultures. Daily visual examination of Malthus curves and subculture of bottles not promptly attached to the apparatus were necessary to avoid missing some positive cultures. False positive rates were 13% for the Malthus system and 2% for the conventional system. The contamination rate was considerably lower in the Malthus system (p less than 0.001). Further development would be necessary for the apparatus to be acceptable for routine screening of blood cultures.     

Recovery of Gram-negative bacilli in stored endotracheal aspirates

This study assessed the recovery rates of Gram-negative bacilli from stored endotracheal aspirates frozen with and without glycerol. Samples frozen with glycerol showed a significant difference in isolate recovery, 89.7% versus 69.2% (P = 0.02). This study demonstrates that it is possible to achieve high recovery rates of potentially pathogenic organisms from endotracheal aspirates when stored with glycerol, thus broadening the scope of active surveillance cultures for both clinical and research purposes.     

Clinical and microbiological characteristics of patients with bacteremia caused by Campylobacter species with an emphasis on the subspecies of C. fetus

Objectives

This study was intended to investigate the clinical and microbiological characteristics of patients with bacteremia caused by Campylobacter species.

Diagnostic performance of blood culture bottles for vitreous culture compared to conventional microbiological cultures in patients with suspected endophthalmitis

The purpose of this investigation was to evaluate the performance of blood culture bottles in comparison to conventional microbiological culture techniques in detecting causative microorganisms of endophthalmitis and to determine their anti-infective susceptibility profiles. All consecutive cases with clinically suspected endophthalmitis in a university-based ophthalmology department between January 2009 and December 2016 were analysed in this retrospective comparative case series. Samples from 247 patients with suspected endophthalmitis underwent microbiological diagnostic work-up. All three culture methods were performed from 140 vitreous specimens. Vitreous fluid specimens were inoculated in blood culture bottles, aerobic and anaerobic broth solutions, and on solid media. Anti-infective susceptibility profiles were evaluated by semi-automated methods and/or gradient diffusion methods. Microorganisms were grown in 82 of 140 specimens for which all methods were performed (59%). Microorganisms were more frequently grown from blood culture bottles (55%) compared to broth solution (45%, p?=?0.007) and solid media (33%, p?<?0.0001). Considerable differences in the performance among culture media were detected for fungal pathogens. All grown fungi were detected by blood culture bottles (11 of 11, 100%). Broth solution recovered 64% and solid media 46% of grown fungi. No Gram-positive bacterium was resistant to vancomycin and all Gram-negative pathogens except for one isolate were susceptible to third-generation cephalosporins. In suspected endophthalmitis patients, blood culture bottles have a higher overall pathogen detection rate from vitreous fluid compared to conventional microbiological media, especially for fungi. The initial intravitreal antibiotic therapy with vancomycin plus third-generation cephalosporins appears to be an appropriate treatment approach for bacterial endophthalmitis.     

Comparison of clinical characteristics of bacteremia from Elizabethkingia meningoseptica and other carbapenem-resistant,non-fermenting Gram-negative bacilli at a tertiary medical center

Background

Acquired carbapenem resistance among non-fermenting Gram-negative bacilli (NFGNB), such as Pseudomonas aeruginosa and Acinetobacter calcoaceticus-Acinetobacter baumannii complex (ACB complex), is a serious problem in nosocomial infections. We previously reported that patients infected with the intrinsically carbapenem-resistant Elizabethkingia meningoseptica were associated with high mortality. However, little information is available regarding the clinical outcome of E. meningoseptica bacteremia when compared to that of other carbapenem-resistant NFGNB.