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

Determinants of time to positivity in bloodstream infections: an analysis of a population-based cohort in Queensland, Australia

PURPOSE

Time to Positivity (TTP) measures the interval from incubation to bacterial growth detection in blood cultures. Although shorter TTP is associated with higher mortality, factors associated with TTP remain uncertain.

METHODS

A retrospective cohort study was conducted among Queensland residents with positive blood cultures between 2000-2019. Incident bloodstream infections (BSIs) were identified using Pathology Queensland data, with demographic, clinical, and outcome data linked to state-wide databases.

RESULTS

The study analysed 84,341 patients with monomicrobial BSI with a median patient age of 65.6 years (IQR 45.4-78.1), and most infections being community-associated (77.0%). Age showed a non-linear relationship with TTP, and male sex was linked with slightly higher TTP (Incidence Rate Ratio (IRR) 1.01; 95% Confidence Intervals (CI) 1.00-1.02; p = 0.011), reflecting a small but measurable association. Liver disease and malignancy were associated with lower TTP (IRR 0.93; 95% CI 0.91-0.95; p < 0.0001 and IRR 0.95; 95% CI 0.94-0.97; p < 0.0001 respectively), whilst diabetes showed no significant difference (IRR 1.01; 95% CI 1.00-1.02; p = 0.0840). Hospital onset infections exhibited longer TTPs (IRR 1.09; 95% CI 1.08-1.10; p < 0.0001).

CONCLUSIONS

There are several host characteristics associated with TTP that may in part explain the complex relationship between this variable and mortality. Beyond microbiological factors such as isolate type, TTP is also influenced by clinical variables including patient demographics and infection characteristics highlighting its potential as a prognostic marker. Further evaluation is needed to clarify its role in predicting patient outcomes and guiding tailored treatment strategies.

Time to Staphylococcus aureus Blood Culture Positivity as a Risk Marker of Infective Endocarditis: A Retrospective Cohort Study

BACKGROUND

Endocarditis occurs in approximately 10%-15% of patients with Staphylococcus aureus bacteremia (SAB). Short time to positivity (TTP) in blood culture flasks has been linked to endocarditis in smaller studies. This study evaluated the association between TTP and endocarditis in SAB in a large cohort.

METHODS

Adult patients with ≥1 S. aureus positive blood culture treated at a tertiary-level, 500-bed hospital in Stockholm, Sweden between 2011-2021 were retrospectively identified. The primary outcome was the presence of infective endocarditis.

RESULTS

A total of 1703 episodes of SAB (23/1703 methicillin-resistant) in 1610 patients were included. Median age was 75 (interquartile range [IQR], 63-84) years and median Charlson comorbidity index score was 2 (IQR, 1-3). Echocardiography was performed in 1102/1703 (65%). Thirty-day mortality was 406/1703 (24%) and endocarditis was found in 154/1703 (9%). Median TTP was shorter in patients with endocarditis (9 [IQR, 7-12] hours) compared to patients without endocarditis (13 [interquartile range, 10-18] hours; P < .001). The risk of endocarditis decreased with 11% per hour (odds ratio [OR], 0.89 [95% confidence interval {CI}, .54-.92]; P < .001) in a univariate analysis using TTP as a continuous variable. In multivariate analysis, TTP <13 hours (the median) was independently associated with endocarditis (OR, 3.59 [95% CI, 2.35-5.3]; P < .001). The negative predictive value of TTP >13 hours for endocarditis was 96% (95% CI, 95%-97%).

CONCLUSIONS

Short TTP was associated with endocarditis. The negative predictive value of >95% suggests that TTP >13 hours can be used to risk-stratify patients with SAB.

Reliability of differential time to positivity technique for diagnosing catheter-related bloodstream infections: a retrospective analysis

The differential time to positivity (DTTP) technique is the recommended conservative procedure to diagnose catheter-related bloodstream infection (C-RBSI). However, its reliability and accuracy remain under debate. Therefore, we aimed to compare the DTTP technique feasibility to detect C-RBSI compared to the catheter culture (CC) method. We conducted a 9-month retrospective study including bacteremic episodes in which both DTTP blood cultures (BC) and CC were obtained. We analyzed the diagnostic validity of the DTTP technique for detecting C-RBSI compared to the gold standard (C-RBSI with CC), along with patient clinical data. We included 37 episodes of C-RBSI where both DTTP BC and CC were obtained. C-RBSI was confirmed by both techniques in only 13 episodes (35.1%), whereas in 11 (29.7%) and 13 (35.1%), only DTTP BC or DTTP BC with CC (with a difference between catheter lumen and peripheral BC growth of <2 hours) was positive, respectively. Therefore, the validity values of the DTTP technique for predicting C-RBSI were as follows: sensitivity, 50.0%; specificity, 71.8%; positive predictive value, 54.2%; and negative predictive value, 68.3%. The distribution of microorganisms was similar among the three groups. All patients in whom colonization was not demonstrated by CC (n = 11) had been receiving antibiotics before catheter withdrawal. DTTP is a conservative technique that might help to diagnose C-RBSI mostly in situations where catheter removal cannot be achieved. However, it should be interpreted with caution and never be used to rule out C-RBSI. CC before starting antimicrobial therapy remains the most reliable method to diagnose and confirm an episode of C-RBSI.IMPORTANCEWe try to clarify the reliability of the differential time to positivity technique to predict C-RBSI. It may be interpreted with caution and considering clinical signs, as some C-RBSI can be misdiagnosed.

Time to positivity as a predictor of catheter-related bacteremia and mortality in adults with Pseudomonas aeruginosa bloodstream infection

BACKGROUND

Time to positivity (TTP) and differential TTP (DTP) emerge as diagnostic and prognostic tools for bloodstream infections (BSI) though specific cut-off values need to be determined for each pathogen. Pseudomonas aeruginosa BSI (PAE-BSI) is of critical concern, particularly in immunocompromised patients, due to high mortality rates. Catheter-related infections are a common cause, necessitating rapid and accurate diagnostic tools for effective management (source-control).

METHODS

Unicentric retrospective observational study analyzing the diagnostic utility and best cut-off values of time to positivity (TTP) and differential time to positivity (DTP) to identify catheter-related PAE-BSI and the association of TTP with 30-day mortality.

RESULTS

1177 PAE-BSI cases TTP were included in the study. TTP was available in all episodes whereas DTP was available in 355 episodes. Breakthrough bacteremia disregarding the TTP, more than one positive blood culture or > 7 days with a catheter in place and both a TTP < 13h and a DTP > 2h were independently associated to catheter-related PAE-BSI. Secondly, lower TTP were significantly associated with higher 30-day mortality rates in both catheter-related and non-catheter-related PAE-BSI. For catheter-related infections, TTP < 14h exacerbated mortality among patients among patients in whom the catheter was not removed within 48h (OR 2.9[1.04-8]); whereas for other sources TTP < 16h increased mortality (OR 1.6[1.1-2.4]) particularly when the empiric antibiotic therapy was not active (OR 3.8[1.5-10]).

CONCLUSION

These findings advocate for the routine use of TTP over DTP as a diagnostic tool to guide timely interventions such as catheter removal, thereby potentially improving patient outcomes in PAE-BSI. Moreover, lower TTP have also prognostic implications in both catheter-related and non-catheter-related infections.

Time to positivity of blood cultures in paediatric patients

AIM

Continuous monitoring of blood culture (BC) systems allows rapid detection of microbial growth. We aimed to determine differences in time to positivity (TTP) in BACTEC BC between organisms and whether a 36-h period was sufficient to detect all relevant pathogenic bacteria for children admitted to a tertiary care paediatric hospital.

METHODS

This was a retrospective audit of positive aerobic (AE) and anaerobic (AN) BC from paediatric inpatients with available TTP from 1 August 2016 to 2 January 2019. First positive BC per bacteraemia episode was analysed.

RESULTS

Overall, 649 BC were positive, of which 480 first positive BC were analysed: 246 AE (51.3%) only, 216 paired (45%) (108 AE and 108 AN) and 18 AN (3.8%) only. There were 372 episodes of bacteraemia in 340 patients. Median age was 19 months (interquartile range (IQR): 1.25-60). Median TTP for AE and AN cultures was 13.20 (IQR: 9.84-18.48) and 13.92 h (IQR: 10.32-17.04), respectively. Organisms were GNR 49.7%, GPC 29.6%, contaminants 14.5%, mixed 3.0%, other 2.4% and yeast 0.8%. Streptococcus agalactiae had the fastest median TTP in AE and AN cultures, followed by Escherichia coli (AE 8.88 vs. 10.20 h). For paired AE and AN cultures, TTP was faster for AE versus AN cultures (13.36 vs. 14.52 h, P = 0.001). A 36-h cut-off time captured 97.7% AE BC and 99.1% AN BC with pathogens, and 86.5% AE BC and 91.7% AN BC with contaminants, respectively.

CONCLUSIONS

GNR were the commonest pathogens in paediatric BC and faster growth was detected in AE versus AN cultures. By 36 h, >97.7% of BC were positive for pathogens versus 86.5% for contaminants.

Diagnostic accuracy of neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio, and neutrophil-lymphocyte-to-platelet ratio biomarkers in predicting bacteremia and sepsis in immunosuppressive patients with cancer: literature review

Background

This literature review explores the role of neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and neutrophil-lymphocyte-to-platelet ratio (NLPR) biomarkers, as potential indicators for predicting bacteremia and sepsis in patients with cancer.

Objective

Tracing the evolution of interest in this area since 2001, the aim of this review was to report a comprehensive overview of current knowledge and gaps, particularly in patients undergoing immunosuppression.

Summary of Findings

The literature research indicates the potential of NLR, PLR, and other biomarkers in diagnosing and predicting sepsis, with some studies emphasizing their value in mortality prediction. A specific focus on bacteremia shows the effectiveness of NLR and PLR as early indicators and prognostic tools, though mostly in noncancer patient populations. While NLR and PLR are promising in general cancer patient populations, the review addresses the challenges in applying these biomarkers to patients with neutropenic and lymphopenic cancer. The NLPR could be considered a significant biomarker for inflammation and mortality risk in various medical conditions, yet its diagnostic accuracy in patients with immunosuppressed cancer is not extensively validated.

Conclusion

This review offers a snapshot of the current research on biomarkers in patients with immunocompromised cancer in the sepsis and bacteremia area. More focused research on their application is necessary. This gap underscores an opportunity for future studies to enhance diagnostic and prognostic capabilities in this high-risk group.

Short turnaround time of seven to nine hours from sample collection until informed decision for sepsis treatment using nanopore sequencing

Bloodstream infections (BSIs) and sepsis are major health problems, annually claiming millions of lives. Traditional blood culture techniques, employed to identify sepsis-causing pathogens and assess antibiotic susceptibility, usually take 2-4 days. Early and accurate antibiotic prescription is vital in sepsis to mitigate mortality and antibiotic resistance. This study aimed to reduce the wait time for sepsis diagnosis by employing shorter blood culture incubation times for BD BACTEC™ bottles using standard laboratory incubators, followed by real-time nanopore sequencing and data analysis. The method was tested on nine blood samples spiked with clinical isolates from the six most prevalent sepsis-causing pathogens. The results showed that pathogen identification was possible at as low as 102-104 CFU/mL, achieved after just 2 h of incubation and within 40 min of nanopore sequencing. Moreover, all the antimicrobial resistance genes were identified at 103-107 CFU/mL, achieved after incubation for 5 h and only 10 min to 3 h of sequencing. Therefore, the total turnaround time from sample collection to the information required for an informed decision on the right antibiotic treatment was between 7 and 9 h. These results hold significant promise for better clinical management of sepsis compared with current culture-based methods.

Time to positivity of blood cultures in bloodstream infections with Streptococcus dysgalactiae and association with outcome

PURPOSE

Invasive infections with Streptococcus dysgalactiae predominantly occur in persons of older age with substantial morbidity and mortality. Time to positivity from blood cultures (TTP) has been shown to be a prognostic indicator in bloodstream infections caused by other beta-haemolytic streptococci. This study aimed to determine any possible association between TTP and outcome in invasive infections due to S. dysgalactiae.

MATERIALS AND METHODS

Episodes of S. dysgalactiae bacteraemia, that occurred during 2015-2018 in the Region of Skåne, Sweden, were identified through the laboratory database and retrospectively studied. Any association with TTP and the primary outcome, death within 30 days and the development of sepsis or disease deterioration within 48 hours from blood culturing as secondary outcomes were investigated.

RESULTS

Among the 287 episodes of S. dysgalactiae bacteraemia, 30-day mortality rate was 10% (n = 30). Median TTP was 9.3 h (interquartile range 8.0-10.3 h). Median TTP was statistically significantly shorter in patients who died within 30 days compared to surviving patients (7.7 vs 9.3 h, p = .001, Mann-Whitney U test). Short TTP(≤ 7.9 h) was still associated with 30-day mortality when adjusting for age, (OR 4.4, 95% CI 1.6-12.2, p = .004). Associations between secondary outcomes and levels of TTP were not observed.

CONCLUSION

TTP may be an important prognostic indicator for 30-day mortality in patients with bloodstream infections due to S. dysgalactiae.

Time to Positivity Facilitates an Early Differential Diagnosis of Candida tropicalis from Other Candida species

Background

Candidemia caused by Candida tropicalis has more serious adverse consequences and an even higher mortality. Time to positivity (TTP) has been widely used to identify microbial species, resistant microorganisms and distinguish real pathogens and pollutants. However, few studies have demonstrated TTP as a presumptive diagnosis of C. tropicalis in patients with candidemia.

Patients and Methods

A retrospective study of 136 episodes of candidemia and simulated blood cultures with 314 episodes of confirmed Candida strains were applied to explore the role of TTPs in diagnosing C. tropicalis. TTPs were recorded as the shorter one if both aerobic and anaerobic vials were positive. Lastly, relationships were tested between TTPs and resistance and initial inocula concentration.

Results

For the retrospective study, the mean of TTPs for C. tropicalis from 136 patients with candidemia was significantly shorter than other Candida species. The area under the receiver operating characteristics (ROC) curve was 0.8896 ± 0.030 with a sensitivity of 92.86% and a specificity of 77.87%, respectively, indicating TTPs with a cut-off value of <25.50 h had a strong diagnostic power for C. tropicalis in patients with candidemia. Moreover, TTPs from 314 simulated blood cultures showed similar results as the retrospective study, demonstrating TTP is a powerful diagnostic tool in early diagnosing C. tropicalis in patients with candidemia. Additionally, our results showed no statistical significance between TTPs and initial inocula concentration and resistance of Candida species, suggesting initial inocula concentration does not impact TTPs, and TTPs may not be promising in predicting the resistance of all Candida species.

Conclusion

TTP can be employed to early distinguish C. tropicalis from other Candida species in patients with candidemia, which is extremely helpful to initiate empiric antifungal treatments to improve clinical outcomes.

Clinical Impact of Time-to-Positivity of Blood Cultures on Mortality in Patients with Pseudomonas aeruginosa Bacteremia

OBJECTIVES

To investigate the impact of the time-to-positivity of blood cultures (TTP) on 30-day mortality in patients with Pseudomonas aeruginosa (PA) bacteremia.

METHODS

All non-duplicated episodes of PA monomicrobial bacteremia in adult patients from January 2013 to February 2020 were analysed. Epidemiological and clinical data were collected. TTP for PA isolates was automatically recorded. Multivariate analysis identified factors predicting 30-day overall mortality.

RESULTS

A total of 328 patients were identified. The median TTP for PA isolates was 15 h (IQR 12-18 h). All MDR/XDR episodes were positive within the first 36 h. The 30-day mortality rate was 32.3%. The best cut-off value of the TTP for predicting mortality was 16 h (AUC 0.62, 95% CI 0.56-0.67, P=0.001). The 30-day mortality rate was significantly higher in the TTP ≤16 h group (41.0% versus 19.5%, P<0.001). In a multivariate analysis, severe neutropenia (aOR 2.67, 95% CI 1.4-5.09, P=0.002), septic shock (aOR 3.21, 95% CI 1.57-5.89, P<0.001), respiratory source (aOR 4.37, 95% CI 2.24-8.52, P<0.001), nosocomial acquisition (aOR 1.99, 95% CI 1.06-3.71, P=0.030), TTP≤ 16 h (aOR 2.27, 95% CI 2.12-4.25, P=0.010) and MDR/XDR phenotype (aOR 2.54, 95% CI 1.38-4.67, P=0.002) were independently associated with 30-day mortality.

CONCLUSIONS

A short TTP (≤16 h) was independently associated with increased 30-day mortality. After local validation, this routinely microbiological parameter might be useful for guiding empirical antipseudomonal therapies and supporting the close monitoring of patients with PA bacteremia.

Considerations in evaluating equipment-free blood culture bottles: A short protocol for use in low-resource settings

Use of equipment-free, “manual” blood cultures is still widespread in low-resource settings, as requirements for implementation of automated systems are often not met. Quality of manual blood culture bottles currently on the market, however, is usually unknown. An acceptable quality in terms of yield and speed of growth can be ensured by evaluating the bottles using simulated blood cultures. In these experiments, bottles from different systems are inoculated in parallel with blood and a known quantity of bacteria. Based on literature review and personal experiences, we propose a short and practical protocol for an efficient evaluation of manual blood culture bottles, aimed at research or reference laboratories in low-resource settings. Recommendations include: (1) practical equivalence of horse blood and human blood; (2) a diverse selection of 10 to 20 micro-organisms to be tested (both slow- and fast-growing reference organisms); (3) evaluation of both adult and pediatric bottle formulations and blood volumes; (4) a minimum sample size of 120 bottles per bottle type; (5) a formal assessment of usability. Different testing scenarios for increasing levels of reliability are provided, along with practical tools such as worksheets and surveys that can be used by laboratories wishing to evaluate manual blood culture bottles.

Short time to positivity of blood culture predicts mortality and septic shock in bacteremic patients: a systematic review and meta-analysis

Background

The value of time to positivity (TTP) on diagnosis for catheter-related bloodstream infection and distinguishment on bacteria group and infection source has been investigated. However, the relationship between TTP and patient outcome requires verification, and we performed a systematic review and meta-analysis.

Methods

We searched PubMed, EMBASE, CINAHL, Cochrane Library, Web of Science for publications associated with the topic. We included studies that researched the TTP on predicting patient mortality and septic shock. Quality assessment is performed with Critical Appraisal Skills Programme (CASP). The analysis is performed using Review Manager Version 5.0.24. on articles available for data extraction on the exact population of each outcome group. The existence of publication bias was assessed by funnel plots. Statistical heterogeneity was evaluated using the Cochran Q and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${I}^{2}$$\end{document}I2 statistics. The outcome is reported as an odds ratio. PROSPERO registration: CRD42021272286.

Results

Twenty-four eligible studies were included in our study. Twenty-four in the mortality group and six in the septic shock group. Mortality is significantly associated with the short time to positivity group with an odds ratio of 2.98 (95% CI: 2.25–3.96, p-value < 0.001). The odds ratio for developing septic shock in the short TTP group is 4.06 (95% CI: 2.41–6.84, p-value < 0.001). Subgroup analysis revealed short TTP as a significant predictor of mortality and septic shock in Gram's positive and Gram's negative related bloodstream infections. TTP is not associated with mortality among patients with candidaemia.

Conclusions

Short time to positivity is a reliable marker for patient outcome in certain bacterial species. Studies concerning confounding factors such as the delay in bottle loading and other confounding factors are needed to enhance external validity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-022-07098-8.

Time to blood, respiratory and urine culture positivity in the intensive care unit: Implications for de-escalation

Objectives

Concern for late detection of bacterial pathogens is a barrier to early de-escalation efforts. The purpose of this study was to assess blood, respiratory and urine culture results at 72 h to test the hypothesis that early negative culture results have a clinically meaningful negative predictive value.

Methods

We retrospectively reviewed all patients admitted to the medical intensive care unit between March 2012 and July 2018 with blood cultures obtained. Blood, respiratory and urine culture results were assessed for time to positivity, defined as the time between culture collection and preliminary species identification. The primary outcome was the negative predictive value of negative blood culture results at 72 h. Secondary outcomes included sensitivity, specificity, positive predictive value and negative predictive value of blood, respiratory and urine culture results.

Results

The analysis included 1567 blood, 514 respiratory and 1059 urine cultures. Of the blood, respiratory and urine cultures ultimately positive, 90.3%, 76.2% and 90.4% were positive at 72 h. The negative predictive value of negative 72-h blood, respiratory and urine cultures were 0.99, 0.82 and 0.97, respectively. Antibiotic de-escalation had good specificity, positive predictive value and negative predictive value for finalized negative cultures.

Conclusion

Negative blood and urine culture results at 72 h had a high negative predictive value. These findings have important ramifications for antimicrobial stewardship efforts and support protocolized re-evaluation of empiric antibiotic therapy at 72 h. Caution should be used in patients with clinically suspected pneumonia, since negative respiratory culture results at 72 h were weakly predictive of finalized negative cultures.

Prognostic Value of the Time-to-Positivity in Blood Cultures from Septic Shock Patients with Bacteremia Receiving Protocol-Driven Resuscitation Bundle Therapy: A Retrospective Cohort Study

Introduction: To evaluate the prognostic value of the time-to-positivity in patients with culture-positive septic shock. Methods: Retrospective study using a prospective data registry was performed at the emergency department of a tertiary hospital. Consecutive adult patients with septic shock (N = 2499) were enrolled between 2014 and 2018. Bacteremia was defined using blood cultures, and viral and fungal pathogens were excluded. The primary outcome was the 28-day mortality. Results: In 803 (46.7%) septic shock patients with bacteremia, median TTP was 10.1 h. The most prevalent isolated bacterial pathogens were Escherichia coli (40.8%) and Klebsiella (23.4%). Although the TTP correlated with a higher sequential organ failure assessment score (Spearman’s rho = −0.12, p < 0.01), it showed no significant difference between the 28-day survivors and non-survivors (10.2 vs. 9.4 days, p = 0.35). In subgroup analysis of the Escherichia coli and Klebsiella bacteremia cases, a shorter TTP showed prognostic value for predicting the 28-day mortality. The optimal TTP cut-off for Escherichia coli and Klebsiella was 10 h and 8 h, respectively. Conclusions: The prognostic value of the TTP in septic shock patients receiving bundle therapy may be limited and its clinical interpretation should only be made on a pathogen-specific basis.

Time to positivity as a prognostic factor in bloodstream infections with Enterococcus spp

Time to positivity (TTP) is the delay of time from incubation to blood culture positivity. Short TTP can predict mortality and source of infection. The aim of this study was to investigate the value of TTP of patients with bloodstream infections with enterococci (E-BSI).In a single centre retrospective cohort study in Germany, the data of 244 patients with monomicrobial E-BSI were analyzed with hospital mortality as the primary outcome of interest from January 1 2014 to December 31 2016. Mortality rate of patients with bloodstream infections (BSI) with E. faecalis was 16.7%, Vancomycin sensitive E. faecium (VSEfm) 26.7% and Vancomycin resistant E. faecium (VREfm) 38.2%. Cut-offs showed a significantly higher mortality rate when compared to longer TTP (E. faecalis: P=0.047; VSEfm: P=0.02), but were not risk factors in survival analysis (E.faecalis: HR (hazard ratio): 2.73; P=0.17; VSEfm: HR: 1.63; P=0.15; VREfm: HR: 1.24; P=0.63). TTP≤10.5 hours with E. faecalis BSI was a discriminator for cardiovascular source of infection (AUC: 0.75). A short TTP could predict mortality rates and source of infection but was not an independent parameter for risk of death in survival analysis.

How do I manage a patient with enterococcal bacteraemia?

BACKGROUND

Enterococcal bacteraemia (EB) is common, particularly in the nosocomial setting, and its management poses a challenge for clinicians and microbiologists.

OBJECTIVES

The aim was to summarize the more relevant features of EB and to provide a practical state-of-the-art on the topics that more directly affect its management.

SOURCES

Pubmed articles from inception to 31 May 2020.

CONTENT

The following topics are covered: epidemiological, clinical and microbiological characteristics and factors associated with prognosis of EB; diagnosis and work-up, including the use of echocardiography to rule out endocarditis; antibiotic management with special focus on antimicrobial resistance and complicated EB; and the role of infectious disease consultation and the use of bundles in EB. In addition, three clinical vignettes are presented to illustrate the practical application of the guidance provided, and major gaps in the current evidence supporting EB management are discussed.

IMPLICATIONS

EB is associated with large burdens of morbidity and mortality, particularly among fragile and immunosuppressed patients presenting complicated bacteraemia due to multidrug-resistant enterococci. Most cases of EB are caused by Enterococcus faecalis, followed by E. faecium. EB often presents as polymicrobial bacteraemia. Rapidly identifying patients at risk of EB is crucial for timely application of diagnostic techniques and empiric therapy. Early alert systems and rapid diagnostic techniques, such as matrix-assisted desorption ionization-time of flight mass spectrometry, especially if used together with infectious disease consultation within bundles, appear to improve management and prognosis of EB. Echocardiography is also key in the work-up of EB and should probably be more extensively used, although its exact indications in EB are still debated. Multidisciplinary approaches are warranted due to the complexity and severity of EB.

Time to positivity of blood cultures among a veteran population: How long to wait before discontinuing antimicrobial therapy when suspicion of infection is low

Time to positivity (TTP) of blood cultures can guide antimicrobial therapy. This single-center retrospective cohort study aimed to determine the yield of clinically significant organisms from blood cultures that were initially negative at 24 hours. Clinically significant organisms were uncommon after 24 hours (1.5%) and more common in intensive care unit settings.

Time to positive culture can differentiate post-neurosurgical coagulase-negative Staphylococci other than S epidermidis meningitis from contamination: A case-control observational study

Objective

To explore the characteristics of coagulase‐negative Staphylococci other than Staphylococci epidermidis (Nse‐CoNS) meningitis and to apply cerebrospinal fluid (CSF) times to positivity culture (TTPC) for the precise differentiation of meningitis from contamination.

Methods

We conducted a case‐control study to accomplish the following: First, we retrospectively reviewed records of post‐neurosurgical patients’ CSF that yielded Nse‐CoNS from January to October 2019 at the Beijing Tiantan Hospital; 17 clinical and 12 laboratory characteristics were reviewed. Second, we investigated the TTPC of the Nse‐CoNS, the cutoffs, and corresponding parameters to differentiate Nse‐CoNS meningitis from contamination.

Results

In this study, a total of 146 patients with Nse‐CoNS CSF culture positive were enrolled. The average TTPC in the Nse‐CoNS meningitis group was significantly shorter than in the contamination group (20.2 ± 5.0 hours and 30.2 ± 12.6 hours, respectively, P < .05). The area under curve (AUC) of the model was 0.802. A TTPC of 20.0 hours had 94.3% sensitivity and a negative value of 90.2% for predicting Nse‐CoNS meningitis.

Conclusions

Nse‐CoNS meningitis often causes confusion in clinical diagnosis. In this study, we evaluated the clinical predictive factors of Nse‐CoNS meningitis and confirmed that the median TTPC in the Nse‐CoNS meningitis group was significantly shorter than in the contamination group. A TTPC shorter than 20.0 hours was associated with Nse‐CoNS meningitis, while a TTPC longer than 20.0 hours was associated with Nse‐CoNS contamination. This information will be helpful for the rapid diagnosis of Nse‐CoNS meningitis.

Performance of differential time to positivity as a routine diagnostic test for catheter-related bloodstream infections: a single-centre experience

OBJECTIVE

To assess the performance of differential time to positivity (DTP) for the diagnosis of catheter-related bloodstream infections (CRBSI).

METHODS

From all episodes of bloodstream infections (BSI) diagnosed during a 15-year period (2003-17) those in which a paired set of blood cultures drawn from a catheter and a peripheral vein were positive for the same microorganism and had a clinically and/or microbiologically defined source were selected. To assess diagnostic discrimination ability and accuracy of DTP for CRBSI, area under the receiver operating characteristic curves (AUC) and performance characteristics of a DTP ≥2 h were computed.

RESULTS

A total of 512 BSI were included, of which 302 (59%) were CRBSI. Discrimination ability of DTP was low for Staphylococcus aureus (AUC 0.656 ± 0.06), coagulase-negative staphylococci (AUC 0.618 ± 0.081), enterococci (AUC 0.554 ± 0.117) and non-AmpC-producing Enterobacteriaceae (AUC 0.653 ± 0.053); moderate for Pseudomonas aeruginosa (AUC 0.841 ± 0.073), and high for AmpC-producing Enterobacteriaceae (AUC 0.944 ± 0.039). For the entire sample, DTP had a low-to-moderate discrimination ability (AUC 0.698 ± 0.024). A DTP ≥2 h has a low sensitivity for coagulase-negative staphylococci (60%) and very low for S. aureus (34%), enterococci (40%) and non-AmpC-producing Enterobacteriaceae (42%). A DTP cut-off of 1 h improved sensitivity (90%) for AmpC-producing Enterobacteriaceae.

CONCLUSIONS

Differential time to positivity performs well for diagnosing CRBSI only when AmpC-producing Enterobacteriaceae and P. aeruginosa are involved. Performance is low for common Gram-positive organisms and non-AmpC-producing enteric bacilli; a negative test should not be used to rule out CRBSI due to these microorganisms. A DTP ≥1 h may improve accuracy for AmpC-producing Enterobacteriaceae, particularly Enterobacter spp.

Time to positivity of blood cultures supports early re-evaluation of empiric broad-spectrum antimicrobial therapy

BACKGROUND

Blood cultures are considered the gold standard to distinguish bacteremia from non-bacteremic systemic inflammation. In current clinical practice, bacteraemia is considered unlikely if blood cultures have been negative for 48-72 hours. Modern BC systems have reduced this time-to-positivity (TTP), questioning whether the time frame of 48-72 hrs is still valid. This study investigates the distribution of TTP, the probability of blood culture positivity after 24 hours, and identifies clinical predictors of prolonged TTP.

METHODS

Adult patients with monomicrobial bacteremia in an academic hospital were included retrospectively over a three-year period. Clinical data were retrieved from the medical records. Predictors of TTP >24 hours were determined by uni- and multivariate analyses. The residual probability of bacteremia was estimated for the scenario of negative BCs at 24 hours after bedside collection.

RESULTS

The cohort consisted of 801 patients, accounting for 897 episodes of bacteremia. Mean age was 65 years (IQR 54-73), 534 (59.5%) patients were male. Median TTP was 15.7 (IQR 13.5-19.3) hours. TTP was ≤24 hours in 85.3% of episodes. Antibiotic pre-treatment (adjusted OR 1.77; 95%CI 1.14-2.74, p<0.01) was independently associated with prolonged TTP. The probability of bacteremia, if BC had remained negative for 24 hours, was 1.8% (95% CI 1.46-2.14).

CONCLUSION

With adequate hospital logistics, the probability of positive blood cultures after 24 hours of negative cultures was low. Combined with clinical reassessment, knowledge of this low probability may contribute to prioritization of the differential diagnosis and decisions on antimicrobial therapy. As a potential antibiotic stewardship tool, this strategy warrants further prospective investigation.

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.

METHODS

BSI episodes were prospectively collected (2003-2017). When a patient experienced more than one BSI, only one episode was randomly chosen. Time elapsed from the beginning of incubation to a positive reading was observed; TTP was recorded when the first bottle had a positive result.

RESULTS

Of the 850 patient-unique episodes, 323 (38%) occurred in acute leukaemia, 185 (21.8%) in non-Hodgkin's lymphoma and 144 (16.9%) in solid neoplasms. Coagulase-negative staphylococci (225; 26.5%), Escherichia coli (207; 26.1%), Pseudomonas aeruginosa (136; 16%), Enterococcus spp. (81; 9.5%) and Klebsiella pneumoniae (67; 7.9%), were the most frequent microorganisms isolated. MDR-GNB were documented in 126 (14.8%) episodes. Median TTP was 12 h (interquartile range 9-16.5 h). Within the first 24 h, 92.1% of blood cultures were positive (783/850). No MDR-GNB was positive over 24 h. Of the 67 (7.9%) episodes with a TTP ≥24 h, 25 (37.3%) occurred in patients who were already receiving active antibiotics against the isolated pathogen. Most common isolations with TTP ≥24 h were coagulase-negative staphylococci, candidaemia and a group of anaerobic GNB.

CONCLUSIONS

Currently, the vast majority of BSI in individuals with onco-haematological diseases with febrile neutropenia have a TTP <24 h, including all episodes caused by MDR-GNB. Our results support reassessing empiric antibiotic treatment in neutropenic patients at 24 h, to apply antibiotic stewardship de-escalation strategies.

Influence of empirical double-active combination antimicrobial therapy compared with active monotherapy on mortality in patients with septic shock: a propensity score-adjusted and matched analysis

Objectives

To evaluate the influence on mortality of empirical double-active combination antimicrobial therapy (DACT) compared with active monotherapy (AM) in septic shock patients.

Methods

A retrospective study was performed of monomicrobial septic shock patients admitted to a university centre during 2010-15. A propensity score (PS) was calculated using a logistic regression model taking the assigned therapy as the dependent variable, and used as a covariate in multivariate analysis predicting 7, 15 and 30 day mortality and for matching patients who received DACT or AM. Multivariate models comprising the assigned therapy group and the PS were built for specific patient subgroups.

Results

Five-hundred and seventy-six patients with monomicrobial septic shock who received active empirical antimicrobial therapy were included. Of these, 340 received AM and 236 DACT. No difference in 7, 15 and 30 day all-cause mortality was found between groups either in the PS-adjusted multivariate logistic regression analysis or in the PS-matched cohorts. However, in patients with neutropenia, DACT was independently associated with a better outcome at 15 (OR 0.29, 95% CI 0.09-0.92) and 30 (OR 0.25, 95% CI 0.08-0.79) days, while in patients with Pseudomonas aeruginosa infection DACT was associated with lower 7 (OR 0.12, 95% CI 0.02-0.7) and 30 day (OR 0.26, 95% CI 0.08-0.92) mortality.

Conclusions

All-cause mortality at 7, 15 and 30 days was similar in patients with monomicrobial septic shock receiving empirical double-active combination therapy and active monotherapy. However, a beneficial influence of empirical double-active combination on mortality in patients with neutropenia and those with P. aeruginosa infection is worthy of further study.

Distribution and clinical determinants of time-to-positivity of blood cultures in patients with neutropenia

OBJECTIVES

Blood cultures (BCs) are essential in the evaluation of neutropenic fever. Modern BC systems have significantly reduced the time-to-positivity (TTP) of BC. This study explores the probability of bacteraemia when BCs have remained negative for different periods of time.

METHODS

All adult patients with neutropenia and bacteraemia were included (January 2012-February 2016). Predictive clinical factors for short (≤16 hours) and long (>24 hours) TTP were determined. The residual probability of bacteraemia was estimated for the scenario of negative BC 24 hours after collection.

RESULTS

The cohort consisted of 154 patients, accounting for 190 episodes of bacteraemia. Median age of 61 years, 60.5% were male. In 123 (64.7%) episodes, BC yielded a single Gram-positive micro-organism and in 49 (25.8%) a Gram-negative micro-organism (median TTP 16.7, 14.5 hours respectively, P < .01). TTP was ≤24 hours in 91.6% of episodes. Central line-associated bacteraemia was associated with long TTP. The probability of bacteraemia if BC had remained negative for 24 hours was 1%-3%.

CONCLUSIONS

The expected TTP offers guidance in the management of patients with neutropenia and suspected bacteraemia. The knowledge of negative BC can support a change in working diagnosis, and impact clinical decisions as soon as 24 hours after BC collection.

Time to blood culture positivity as a predictor of clinical outcomes and severity in adults with bacteremic pneumococcal pneumonia

OBJECTIVES

We aimed to investigate the association between the time to positivity of blood culture (TTP) with clinical outcome and severity of pneumococcal bacteremic pneumonia.

METHODS

Prospective observational study carried out in 278 hospitalized adult CAP patients with positive blood culture for Streptococcus pneumonia (2003-2015).

RESULTS

A total of 278 cases of bacteremic pneumococcal pneumonia were analyzed, median age 62 (46; 79) years. Fifty-one percent of the cases had PSI IV-V. Twenty-one (8%) died within 30-days after admission. The analysis of the TTP showed that the first quartile of the TTP (9.2h) was the best cut-off for differentiating 2 groups of patients at risk, early (TTP <9.2 h) and late (TTP ≥9.2 h) detection groups (AUC 0.66 [95% CI 0.53 to 0.79]). Early TTP was associated with a statistically significant risk of invasive mechanical ventilation (18% vs. 6%, p = 0.007), longer length of hospital stay (12 days vs. 8 days, p<0.001), higher in-hospital mortality (15% vs. 4%, p = 0.010), and 30-day mortality (15% vs. 5%, p = 0.018). After adjustment for potential confounders, regression analyses revealed early TTP as independently associated with high risk of invasive mechanical ventilation (OR 4.60, 95% CI 1.63 to 13.03), longer length of hospital stay (β 5.20, 95% CI 1.81 to 8.52), higher in-hospital mortality (OR 5.35, 95% CI 1.55 to 18.53), and a trend to higher 30-day mortality (OR 2.47, 95% CI 0.85 to 7.21) to be a contributing factor.

CONCLUSION

Our results demonstrate that TTP is an easy to obtain surrogate marker of the severity of pneumococcal pneumonia and a good predictor of its outcome.

Rapid Diagnosis of Staphylococcal Catheter-Related Bacteraemia in Direct Blood Samples by Real-Time PCR

Catheter-related bacteremia (CRB) is an important cause of morbidity and mortality among hospitalized patients, being staphylococci the main etiologic agents. The objective of this study was to assess the use of a PCR-based assay for detection of staphylococci directly from blood obtained through the catheter to diagnose CRB caused by these microorganisms and to perform a cost-effectiveness analysis. A total of 92 patients with suspected CRB were included in the study. Samples were obtained through the catheter. Paired blood cultures were processed by standard culture methods and 4 ml blood samples were processed by GeneXpert-MRSA assay for the detection of methicillin-susceptible (MSSA) or methicillin-resistant (MRSA) Staphylococcus aureus, and methicillin-resistant coagulase-negative staphylococci (MR-CoNS). Sixteen CRB caused by staphylococci were diagnosed among 92 suspected patients. GeneXpert detected 14 out of 16 cases (87.5%), including 4 MSSA and 10 MR-CoNS in approximately 1 hour after specimen receipt. The sensitivity and specificity of GeneXpert were 87.5% (CI 95%: 60.4-97.8) and 92.1% (CI 95%: 83-96.7), respectively, compared with standard culture methods. The sensitivity of GeneXpert for S. aureus was 100%. Regarding a cost-effectiveness analysis, the incremental cost of using GeneXpert was of 31.1€ per patient while the incremental cost-effectiveness ratio of GeneXpert compared with blood culture alones was about 180€ per life year gained. In conclusion, GeneXpert can be used directly with blood samples obtained through infected catheters to detect S. aureus and MR-CoNS in approximately 1h after sampling. In addition, it is cost-effective especially in areas with high prevalence of staphylococcal CRB.

Rapid Time to Positivity of Cerebrospinal Fluid Culture with Coagulase-Negative Staphylococcus Is More Likely to Reflect a True Infection Than Contamination

OBJECTIVE

Cerebrospinal fluid (CSF) culture is the gold standard for diagnosing postoperative central nervous system infection. The time to positivity (TTP) of an automated continuous blood culture system may indicate the original concentration of the organism. Coagulase-negative Staphylococcus (CoNS), the common organism recovered in CSF, poses difficulty in differentiating infection from contamination. This study investigated the TTP of CSF culture with CoNS and its relationship to clinical parameters and prognosis.

METHODS

Adult neurosurgical patients with CoNS who recovered via the use of CSF culture in BacT/ALERT Pediatric FAN blood culture bottles and were admitted from September 2013 to July 2015 were enrolled. The demographics, clinical and microbiological data, and treatment were reviewed, and the TTP of each culture was retrieved.

RESULTS

Thirty-nine adult patients with CoNS recovered from CSF culture were included. The TTP ranged from 7.68 to 57.36 hours. A univariate logistic regression analysis indicated patients with rapid TTP (<21.5 hours) compared with those with longer TTP were more likely to be female, show an effective response to antibiotic therapy within 7 days, have clean-contaminated surgical incisions, and show CSF leak. A multivariate logistic regression analysis indicated that being female, an effective antibiotic therapy within 7 days, and clean-contaminated surgical incisions were independent predictors of rapid TTP.

CONCLUSIONS

Targeted antibiotic therapy was more likely to be beneficial to patients with a rapid TTP within 7 days, which suggested that CoNS with a rapid TTP represents the pathogen of central nervous system infection rather than contamination in neurosurgical patients.

Time to positivity of blood culture and its prognostic value in bloodstream infection

The purpose of this study was to investigate the relationship between the time to positivity (TTP) of blood cultures and outcome in patients with bloodstream infections (BSIs). Between January 1st, 2011 and December 31st, 2013, the blood cultures of inpatients with BSI or catheter-related BSI were collected at Peking University Third Hospital. The TTP of different isolates was analyzed, and the relationship between the TTP of isolates and outcome of patients with Enterobacter BSI was retrospectively analyzed. We analyzed the TTP of 886 isolates. Escherichia coli has the shortest (11.97 ± 10.06 h) and Candida has the longest first TTP (61.62 ± 42.77 h). 68.01 % of isolates reached positivity within 24 h and 88.33 % within 48 h. Over 90 % of E. coli isolates reached positivity within 24 h. Over 50 % of Candida isolates reached positivity within 48 h. The TTP differed significantly between cultures that were single or double positive for coagulase-negative staphylococci isolates, Enterobacteriaceae, and Pseudomonas aeruginosa, and between aerobic and anaerobic cultures of E. coli (p < 0.05). However, the TTP did not differ significantly between coagulase-negative staphylococci (double positivity) and Staphylococcus aureus. The best TTP threshold for prediction of mortality from Enterobacter species BSI was 16.3 h [area under the curve (AUC) 0.730, 95 % confidence interval (CI) 0.557, 0.864, sensitivity 100 %, specificity 44.4 %]. The TTP of clinical isolates may represent a valuable marker of the clinical significance of BSIs. Laboratories and clinics should consider using the TTP to predict the prognosis of patients with BSI by bacteria, including Enterobacter and other species.

Serum procalcitonin levels in combination with (1)H NMR spectroscopy: A rapid indicator for differentiation of urosepsis

BACKGROUND

Urosepsis, a severe form of sepsis requires immediate medical attention for prognosis. It is clinically diagnosed by estimating serum procalcitonin (PCT) levels along with time taking urine and blood cultures. We explored NMR based profiling, deriving metabolites that could potentially aid diagnosis.

METHODS

The proton NMR of serum and urine samples of healthy control subjects (n=32) and urosepsis cases (n=35) based on PCT levels, were analyzed. Four clinically identified non-urosepsis cases with high PCT levels were also differentiated through principal component analysis (PCA) of the serum samples.

RESULTS

Quantification of serum and urine through Discriminant Function Analysis (DFA) afforded 93.7% and 91.7% correct classification respectively, along with identification of malonate and urea as potential biomarkers for the disease in both urine and serum samples. The partial least square discriminant analysis (PLS-DA) showed an R(2) value of 0.97 in both biofluids with Q(2)=0.87 and 0.85 for serum and urine respectively. The training set of serum samples provided precise prediction of the test set in a small cohort through random re-sampling method, while in urine samples, the predictions were inconclusive.

CONCLUSIONS

Our pilot study reveals that (1)H NMR of serum metabolic profiling in combination with PCT levels may provide a rapid method for differentiation of urosepsis.

Time-to-positivity of blood culture: An independent prognostic factor of monomicrobial Pseudomonas aeruginosa bacteremia

BACKGROUND/PURPOSE

Pseudomonas aeruginosa bacteremia is an important cause of nosocomial infections with high morbidity and mortality. Time-to-positivity (TTP) of blood cultures is considered to be a predictor of the clinical outcome for bacteremia. The aim of the study is to investigate the relationship between TTP and clinical outcomes in patients with monomicrobial P. aeruginosa bacteremia.

METHODS

From January 2013 to June 2014, a retrospective cohort study was conducted in a 1200-bed tertiary care hospital. The cases of monomicrobial P. aeruginosa bacteremia were studied. TTP and clinical parameters were determined and analyzed.

RESULTS

In 139 cases of P. aeruginosa bacteremia, TTP ≤ 13 hours was associated with higher Pitt bacteremia scores (5.3 ± 4.2 vs. 2.3 ± 2.8, p < 0.001), severe sepsis (66.1% vs. 35.0%, p < 0.001), higher 30-day mortality rate (54.2% vs. 15.0%, p < 0.001), longer hospitalization in the survivors (25.6 ± 48.5 days vs. 16.3 ± 15.3 days, p = 0.16), and more admission to intensive care unit (27.2% vs. 16.3%, p = 0.14). Risk factors for 30-day mortality in the univariate analysis included corticosteroid exposure, primary bacteremia, concurrent pneumonia, a high Pitt bacteremia score, severe sepsis, and TTP ≤ 13 hours. In the multivariate analysis, primary bacteremia, a pulmonary origin of bacteremia, severe sepsis, and TTP ≤ 13 hours were independent risk factors for 30-day mortality.

CONCLUSION

In cases of monomicrobial P. aeruginosa bacteremia, a short TTP (≤ 13 hours) provides prognostic information, in addition to clinical parameters.

Time to positivity in blood cultures of adults with nontyphoidal Salmonella bacteremia

BACKGROUND

Nontyphoidal Salmonella (NTS) is an important bacterial etiology of diarrheal disease, and it causes invasive diseases in immunocompromised hosts. For bacteremia from some species, blood culture with a rapid time to positivity (TTP) is associated with greater mortality. This study investigated TTP of NTS bacteremia and its relationship to clinical parameters and prognosis.

METHODS

Adult patients with NTS bacteremia who were admitted to a tertiary care facility in northern Taiwan from January 2010 to December 2012 were enrolled. Demographics, clinical and microbiological characteristics, and treatment response were reviewed. The TTP for each patient was retrieved from the automated machine.

RESULTS

Sixty-six adult patients (mean age, 66.1 years; range, 27-96 years) with NTS bacteremia were identified by the following serogroup distributions: serogroup B (23.4%), serogroup C1 (1.6%), serogroup C2 (6.3%), and serogroup D (68.8%). The in-hospital mortality, 14-day mortality, and 30-day mortality were 15.2%, 7.6%, and 12.1%, respectively. The TTP ranged 6.5-41.7 hours (median: 11.5 hours). Patients with rapid TTP (less than 10 hours), compared to patients without rapid TTP, were more likely to have liver cirrhosis (31.6% vs. 6.4%, p = 0.013), endovascular lesions (21.1% vs. 4.3%, p = 0.05), higher bacteremia score, intensive care unit admission (57.9% vs. 25.5%, p = 0.021), and septic shock (63.2% vs. 12.8%, p < 0.001). There were no significant differences in the in-hospital mortality and 14-day mortality between patients with TTP <10 hours and patients with TTP ≥10 hours.

CONCLUSION

The TTP of blood cultures, interpreted with a cut-off point of <10 hours, in patients with NTS bacteremia may provide useful diagnostic and prognostic information.

Time to positivity and detection of growth in anaerobic blood culture vials predict the presence of Candida glabrata in candidemia: a two-center European cohort study

This study shows the accuracy of exclusive or earlier growth in anaerobic vials to predict Candida glabrata in a large series of candidemic patients from two European hospitals using the Bactec 9240 system. Alternatively, C. glabrata can be predicted by a time to positivity cutoff value, which should be determined for each setting.

Rapid identification of pneumococci, enterococci, beta-haemolytic streptococci and S. aureus from positive blood cultures enabling early reports

Background

The aim of this study was to evaluate diagnostic tests in order to introduce a diagnostic strategy to identify the most common gram-positive bacteria (pneumococci, enterococci, β-haemolytic streptococci and S. aureus) found in blood cultures within 6 hours after signalling growth.

Methods

The tube coagulase test was optimized and several latex agglutination tests were compared and evaluated before a validation period of 11 months was performed on consecutive positive blood culture patient samples from Kalmar County Hospital, Sweden.

Results

During the validation period 150 (91%) of a total of 166 gram-positive cocci (119 in clusters, 45 in chains or pairs and 2 undefined morphology) were correctly identified as S. aureus, CoNS, Pneumococci, Enterococci or group A streptococci (GAS), group B streptococci (GBS), group G streptococci (GGS) within 6 hours with a minimal increase in work-load and costs. The remaining samples (9%) were correctly identified during the next day. No samples were incorrectly grouped with this diagnostic strategy and no patient came to risk by early reporting.

Conclusion

A simple strategy gives reliable and cost-effective reporting of >90% of the most common gram-positive cocci within 6 hours after a blood cultures become positive. The high specificity of the tests used makes preliminary reports reliable. The reports can be used to indicate the focus of infection and not the least, support faster administration of proper antimicrobial treatment for patients with serious bacterial infections.

Time to positivity of blood cultures supports antibiotic de-escalation at 48 hours

BACKGROUND

Appropriate de-escalation of empirical antimicrobial therapy is a fundamental component of antimicrobial stewardship. Concern for the late detection of bloodstream pathogens may undermine early streamlining efforts and subject patients to protracted courses of nonessential therapy.

OBJECTIVE

To quantify the prevalence of bacterial bloodstream infection (BSI) detection after more than 48 hours of culture incubation. We also assessed the impact of antimicrobial therapy delivered prior to blood sample collection.

METHODS

We retrospectively evaluated time to blood culture positivity (TTP) in adult patients at an academic tertiary care hospital. Microbiology reports were reviewed to identify the TTP for the first positive blood culture bottle for each episode of BSI occurring from February 1, 2011, to July 31, 2011. Isolates were classified as true pathogens or contaminants. Blood culture results after 48 hours of incubation were compared with results after 120 hours of incubation.

RESULTS

The median TTP of 416 monomicrobial BSIs and 210 contamination episodes was 13.7 and 24.4 hours, respectively (P < .001). The median TTPs in those who received and did not receive prior antibiotics were 17.0 and 12.8 hours, respectively (P < .001). By 48 hours, 98% of aerobic Gram-positive and Gram-negative BSIs were detected. Culture results at 48 hours were 97% sensitive and had a negative predictive value of 99.8%.

CONCLUSION

Few true BSIs are detected after more than 48 hours of culture incubation. Clinicians may adjust empirical antibiotic coverage at this time with little risk for subsequent bacterial pathogen detection.

Risk factors for septic shock in acute obstructive pyelonephritis requiring emergency drainage of the upper urinary tract

PURPOSE

To assess the risk factors for septic shock in patients with acute obstructive pyelonephritis requiring emergency drainage of the upper urinary tract.

METHODS

We retrospectively reviewed the records of 48 patients who underwent emergency drainage of the upper urinary tract for sepsis associated with acute obstructive pyelonephritis at our institute. Univariate and multivariate analyses were performed to identify the risk factors.

RESULTS

Among 54 events of sepsis, we identified 20 events of septic shock requiring vasopressor therapy. Cases with shock were more likely than those without shock to have ureteral stone (70 vs 38%, p = 0.024) and positive blood culture results (81 vs 28%, p = 0.006). They received drainage significantly earlier than those without shock (1.0 vs 3.5 days, p < 0.001). Univariate analysis demonstrated that acute obstructive pyelonephritis by ureteral stone, rapid progression (the occurrence of symptoms to drainage ≤ 1 day), positive blood culture, leukocytopenia (<4,000/mm(3)), thrombocytopenia (<120,000/mm(3)), and prothrombin time international normalized ratio ≥ 1.20 were correlated with septic shock. Multivariate logistic regression analysis identified thrombocytopenia (p = 0.005) and positive blood culture (p = 0.040) as independent risk factors for septic shock.

CONCLUSIONS

Thrombocytopenia and positive blood culture were independent risk factors for septic shock in acute obstructive pyelonephritis requiring emergency drainage. Thrombocytopenia would be practically useful as a predictor of septic shock.

Usefulness of time-to-positivity in aerobic and anaerobic vials to predict the presence of Candida glabrata in patients with candidaemia

OBJECTIVES

To determine whether time-to-positivity (TTP) in aerobic and anaerobic blood culture vials is useful to predict the presence of Candida glabrata in patients with candidaemia.

METHODS

TTP was recorded for both aerobic and anaerobic vials for each blood culture set of monomicrobial candidaemia. We considered TTP as the shortest time registered for any positive vial. Two diagnostic criteria were evaluated: the cut-off TTP value as obtained from a receiver operating characteristic curve and the detection of growth only or with a shorter TTP in anaerobic vials.

RESULTS

A total of 157 episodes were analysed of which 19 (12.1%) were due to C. glabrata. The TTP for C. glabrata was longer than that for other species. C. glabrata grew more frequently than other species in anaerobic vials [9/19 (47%) versus 19/138 (14%); P = 0.001] and also more often exclusively or earlier in anaerobic vials [7/19 (37%) versus 5/138 (4%); P < 0.0001]. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of a TTP >56.5 h for predicting the presence of C. glabrata were 47%, 88%, 36% and 92%, respectively. Growth detection only or earlier in anaerobic flasks had a sensitivity of 37%, a specificity of 96%, a PPV of 58% and an NPV of 92%.

CONCLUSIONS

Using the BACTEC 9240 system, a TTP ≤ 56.5 h is useful to rule out C. glabrata. In addition, in settings with an ~12% prevalence of C. glabrata candidaemia, yeast detection exclusively or earlier in anaerobic vials increases the probability of the presence of C. glabrata to 58%, which may be useful for early treatment optimization.

Time to positivity as prognostic tool in patients with Pseudomonas aeruginosa bloodstream infection

OBJECTIVES

The time to positivity (TTP), measured as the time span between the start of incubation and the alert signal from the blood culture device, has been described as useful tool of prognosis in patients suffering from blood stream infection with Staphylococcus aureus, Escherichia coli and Klebsiella pneumonia. The present study investigates the relationship between TTP and in-hospital mortality in patients with monomicrobial Pseudomonas aeruginosa blood stream infection (PA-BSI).

METHODS

From 2006 until 2012 a retrospective cohort study was undertaken in 3 hospitals in the region surrounding Tübingen, Germany. Seventy-four patients with monomicrobial PA-BSI were studied. TTP and clinical parameters were determined and analyzed by receiver operating characteristic (ROC) analysis and Cox regression.

RESULTS

The in-hospital mortality of our clinical cohort was 33.78%. In multivariate Cox regression, a TTP ≤ 18 h proved to be independently associated with mortality (HR 3.83, P = 0.012) along with SAPS II score (HR 1.04, P = 0.006), cardiac disease (HR 0.33, P = 0.008) and appropriate definitive antimicrobial treatment (HR 0.21, P = 0.013).

CONCLUSIONS

TTP is an easy-to-measure laboratory tool for prognosis in patients with monomicrobial PA-BSI, providing useful information in addition to clinical parameters.

Time-to-positivity-based discrimination between Enterobacteriaceae, Pseudomonas aeruginosa and strictly anaerobic Gram-negative bacilli in aerobic and anaerobic blood culture vials

Time-to-positivity (TTP) of first positive blood cultures growing Gram-negative bacilli (GNB) was investigated. When anaerobic vials were positive first, TTP ≤ 18 h differentiated Enterobacteriaceae from strict anaerobic Gram-negative bacilli (PPV 98.8%). When the aerobic ones were first, TTP ≤ 13 h differentiated Enterobacteriaceae from Pseudomonas aeruginosa and other GNB (PPV 80.8%).

Differentiating rapid- and slow-growing mycobacteria by difference in time to growth detection in liquid media

Nontuberculous mycobacteria (NTM) are classified into 2 categories: slow-growing mycobacteria (SGM) and rapid-growing mycobacteria (RGM), based on interval to colony formation by subculture on solid media. However, little is known about the growth rate of NTM in liquid broth media. We evaluated the differences in time to growth detection (TGD) of RGM and SGM in liquid broth media according to acid-fast stain. Among the 696 NTM isolates, 201 were RGM and 495 were SGM. In acid-fast bacilli (AFB)-negative specimens, the mean TGD was 133 h for RGM and 269 h for SGM (P < 0.001). In AFB-positive specimens, the mean TGD was 112 ± 37 h for RGM and 155 ± 125 h for SGM (P = 0.063). In the AFB-negative group, a cut-off value of 6 days was most effective for distinguishing SGM from RGM; however, in the AFB-positive group, an appropriate cut-off value was hard to define with TGD only.