A multicenter trial to compare blood culture with polymerase chain reaction in severe human sepsis

Accuracy of LightCycler(®) SeptiFast for the detection and identification of pathogens in the blood of patients with suspected sepsis: a systematic review and meta-analysis

PURPOSE

There is an urgent need to develop diagnostic tests to improve the detection of pathogens causing life-threatening infection (sepsis). SeptiFast is a CE-marked multi-pathogen real-time PCR system capable of detecting DNA sequences of bacteria and fungi present in blood samples within a few hours. We report here a systematic review and meta-analysis of diagnostic accuracy studies of SeptiFast in the setting of suspected sepsis.

METHODS

A comprehensive search strategy was developed to identify studies that compared SeptiFast with blood culture in suspected sepsis. Methodological quality was assessed using QUADAS. Heterogeneity of studies was investigated using a coupled forest plot of sensitivity and specificity and a scatter plot in receiver operator characteristic space. Bivariate model method was used to estimate summary sensitivity and specificity.

RESULTS

From 41 phase III diagnostic accuracy studies, summary sensitivity and specificity for SeptiFast compared with blood culture were 0.68 (95 % CI 0.63-0.73) and 0.86 (95 % CI 0.84-0.89) respectively. Study quality was judged to be variable with important deficiencies overall in design and reporting that could impact on derived diagnostic accuracy metrics.

CONCLUSIONS

SeptiFast appears to have higher specificity than sensitivity, but deficiencies in study quality are likely to render this body of work unreliable. Based on the evidence presented here, it remains difficult to make firm recommendations about the likely clinical utility of SeptiFast in the setting of suspected sepsis.

Monitoring infection: from blood culture to polymerase chain reaction (PCR)

In patients with sepsis, diagnosis of blood stream infection (BSI) is a key concern to the therapist. Direct verification of pathogens in the blood stream executed by blood cultures (BC) still is regarded as the gold standard up to date. The quickest possible initiation of an appropriate antimicrobial therapy is a cornerstone of an effective therapy. Moreover, in this view BC can also serve to identify antimicrobial agents to target the pathogen. However, when employing BC the time needed until microbiological results are available ranges from 24 up to 72 h. Moreover, infections caused by multiple pathogens often remain undetected and concurrent antibiotic therapy may lower the overall sensitivity. Alternative pathogen characterization can be performed by polymerase chain reaction (PCR) based amplification methods. Results using PCR can be obtained within 6-8 h. Therefore, the time delay until an appropriate therapy can be reduced enormously. Moreover, these methods have the potential to enhance the sensitivity in the diagnosis of blood stream infections. Therefore, PCR based methods might be a valuable adjunct to present procedures of diagnosing bacteraemia.

Quantitative data from the SeptiFast real-time PCR is associated with disease severity in patients with sepsis

Background

The commercial test, SeptiFast, is designed to detect DNA from bacterial and fungal pathogens in whole blood. The method has been found to be specific with a high rule-in value for the early detection of septic patients. The software automatically provides information about the identified pathogen, without quantification of the pathogen. However, it is possible to manually derive Crossing point (Cp) values, i.e. the PCR cycle at which DNA is significantly amplified. The aim of this study was to find out whether Cp values correlate to disease severity.

Methods

We used a study cohort of patients with positive results from SeptiFast tests for bacteria from a recent study which included patients with suspected sepsis in the Emergency department. Cp values were compared with disease severity, classified as severe sepsis/septic shock or non-severe sepsis, according to the criteria of the American College of Chest Physicians/Society of Critical Care Medicine.

Results

Ninety-four patients were included. The prevalence of severe sepsis/septic shock in the study was 29%. SeptiFast positive tests from patients with severe sepsis/septic shock had significantly lower Cp values compared with those from patients with non-severe sepsis, median 16.9 (range: 7.3 - 24.3) versus 20.9 (range: 8.5 - 25.0), p < 0.001. Positive predictive values from the SeptiFast test for identifying severe sepsis/septic shock were 34% at Cp cut-off <25.0, 35% at Cp cut-off <22.5, 50% at Cp cut-off <20.0, and 73% at Cp cut-off <17.5. Patients with a positive Septifast test with a Cp value <17.5 had significantly more severe sepsis/septic shock (73% versus 15%, p < 0.001), were more often admitted to the Intensive Care Unit (23% versus 4%, p = 0.016), had positive blood culture (BC) more frequently (100% versus 32%, p < 0.001) and had longer hospital stays (median 19.5 [range: 4 - 78] days versus 5 [range: 0 - 75] days, p < 0.001) compared with those with a Cp value >17.5.

Conclusions

Our results suggest that introducing quantitative data to the SeptiFast test could be of value in assessing sepsis severity. Moreover, such data might also be useful in predicting a positive BC result.

Molecular diagnosis of sepsis: New aspects and recent developments

By shortening the time to pathogen identification and allowing for detection of organisms missed by blood culture, new molecular methods may provide clinical benefits for the management of patients with sepsis. While a number of reviews on the diagnosis of sepsis have recently been published we here present up-to-date new developments including multiplex PCR, mass spectrometry and array techniques. We focus on those techniques that are commercially available and for which clinical studies have been performed and published.

Rapid diagnosis of sepsis

Fast and appropriate therapy is the cornerstone in the therapy of sepsis. However, the discrimination of sepsis from non-infectious causes of inflammation may be difficult. Biomarkers have been suggested to aid physicians in this decision. There is currently no biochemical technique available which alone allows a rapid and reliable discrimination between sepsis and non-infectious inflammation. Procalcitonin (PCT) is currently the most investigated biomarker for this purpose. C-reactive protein and interleukin 6 perform inferior to PCT in most studies and their value in diagnosing sepsis is not defined. All biomarkers including PCT are also released after various non-infectious inflammatory impacts. This shortcoming needs to be taken into account when biomarkers are used to aid the physician in the diagnosis of sepsis. Polymerase chain reaction (PCR) based pathogen detection may improve time to adequate therapy but cannot rule out the presence of infection when negative.

Use of a multiplex polymerase chain reaction system for enhanced bloodstream pathogen detection in thoracic transplantation

BACKGROUND

Bloodstream infections (BSIs) constitute a frequent post-transplant complication in thoracic allograft recipients, especially during the early post-surgical period when patients are under intense immunosuppression. Thus, early and accurate identification of the responsible pathogens is of critical importance for patient survival. In this study we investigated the potential clinical utility of a multiplex real-time polymerase chain reaction (PCR) technology (SeptiFast; Roche Diagnostics) for the detection of BSIs in a cohort of thoracic allograft recipients.

METHODS

Our observational study included analysis of 130 blood samples from 30 thoracic allograft recipients (23 heart and 7 lung) using SeptiFast in parallel with blood culture. Samples were drawn when there were clinical and laboratory signs of BSI. The applied molecular assay has been designed to allow direct detection of a wide panel of Gram-positive and Gram-negative bacteria and fungi in blood samples.

RESULTS

Real-time PCR yielded concurrent negative and positive results with blood culture methodology in 113 (86.9%) and 5 (3.9%) samples, respectively, with 100% concordance in species identification. SeptiFast identified microorganisms in 9 (6.9%) additional samples that were negative by blood culture. The combined use of SeptiFast and blood culture during the early post-transplant period (<2 months) significantly increased the number of positive samples detected to 17.9% (14 of 78) from 7.7% (6 of 78) detected by blood culture alone (p < 0.05). SeptiFast results were available, on average, within 6 hours from sample collection.

CONCLUSIONS

The PCR-based SeptiFast test is a valuable addition to the traditional blood culture method for rapid etiologic diagnosis of BSIs in thoracic transplant recipients, especially during the early post-transplant period.

Unrevealing culture-negative severe sepsis

Sepsis involves a wide array of sources and microorganisms, only a fraction of which are microbiologically documented. Culture-negative sepsis poses special diagnostic challenges to both clinicians and microbiologists and further questions the validity of sepsis definitions.

Proximal bacterial lysis and detection in nanoliter wells using electrochemistry

Rapid and direct genetic analysis of low numbers of bacteria using chip-based sensors is limited by the slow diffusion of mRNA molecules. Long incubation times are required in dilute solutions in order to collect a sufficient number of molecules at the sensor surface to generate a detectable signal. To overcome this barrier here we present an integrated device that leverages electrochemistry-driven lysis less than 50 μm away from electrochemical nucleic acid sensors to overcome this barrier. Released intracellular mRNA can diffuse the short distance to the sensors within minutes, enabling rapid and sensitive detection. We validate this strategy through direct lysis and detection of E. coli mRNA at concentrations as low as 0.4 CFU/μL in 2 min, a clinically relevant combination of speed and sensitivity for a sample-to-answer molecular analysis approach.

The potential for PCR based testing to improve diagnosis and treatment of sepsis

Early and appropriate antibiotic use is critical for the treatment of sepsis. In practice, however, early antibiotic administration is hampered by diagnostic uncertainty with regard to both early diagnosis of disease and delayed or absent microbiological results. The diagnostic uncertainty often persists into the later stages of sepsis when clinical response to antibiotic treatment is assessed. Blood culture, the current "gold standard" test for diagnosis of sepsis, is inadequate due to low sensitivity and delayed results. However, despite this, the technology remains entrenched in microbiology laboratories due to decades of accumulated experience with the technique. However, in recent years there has been increasing experience with testing based on polymerase chain reaction (PCR). As the technology continues to improve, PCR testing is becoming faster and more sensitive. Moreover, PCR technologies that quantify bacterial load may enable monitoring of response to treatment and susceptibility testing.

Characteristics and outcomes of culture-negative versus culture-positive severe sepsis

INTRODUCTION

Culture-negative sepsis is a common but relatively understudied condition. The aim of this study was to compare the characteristics and outcomes of culture-negative versus culture-positive severe sepsis.

METHODS

This was a prospective observational cohort study of 1001 patients who were admitted to the medical intensive care unit (ICU) of a university hospital from 2004 to 2009 with severe sepsis. Patients with documented fungal, viral, and parasitic infections were excluded.

RESULTS

There were 415 culture-negative patients (41.5%) and 586 culture-positive patients (58.5%). Gram-positive bacteria were isolated in 257 patients, and gram-negative bacteria in 390 patients. Culture-negative patients were more often women and had fewer comorbidities, less tachycardia, higher blood pressure, lower procalcitonin levels, lower Acute Physiology and Chronic Health Evaluation II (median 25.0 (interquartile range 19.0 to 32.0) versus 27.0 (21.0 to 33.0), P = 0.001) and Sequential Organ Failure Assessment scores, less cardiovascular, central nervous system, and coagulation failures, and less need for vasoactive agents than culture-positive patients. The lungs were a more common site of infection, while urinary tract, soft tissue and skin infections, infective endocarditis and primary bacteremia were less common in culture-negative than in culture-positive patients. Culture-negative patients had a shorter duration of hospital stay (12 days (7.0 to 21.0) versus 15.0 (7.0 to27.0), P = 0.02) and lower ICU mortality than culture-positive patients. Hospital mortality was lower in the culture-negative group (35.9%) than in the culture-positive group (44.0%, P = 0.01), the culture-positive subgroup, which received early appropriate antibiotics (41.9%, P = 0.11), and the culture-positive subgroup, which did not (55.5%, P < 0.001). After adjusting for covariates, culture positivity was not independently associated with mortality on multivariable analysis.

CONCLUSIONS

Significant differences between culture-negative and culture-positive sepsis are identified, with the former group having fewer comorbidities, milder severity of illness, shorter hospitalizations, and lower mortality.

Biomarkers of sepsis

Sepsis is an unusual systemic reaction to what is sometimes an otherwise ordinary infection, and it probably represents a pattern of response by the immune system to injury. A hyper-inflammatory response is followed by an immunosuppressive phase during which multiple organ dysfunction is present and the patient is susceptible to nosocomial infection. Biomarkers to diagnose sepsis may allow early intervention which, although primarily supportive, can reduce the risk of death. Although lactate is currently the most commonly used biomarker to identify sepsis, other biomarkers may help to enhance lactate’s effectiveness; these include markers of the hyper-inflammatory phase of sepsis, such as pro-inflammatory cytokines and chemokines; proteins such as C-reactive protein and procalcitonin which are synthesized in response to infection and inflammation; and markers of neutrophil and monocyte activation. Recently, markers of the immunosuppressive phase of sepsis, such as anti-inflammatory cytokines, and alterations of the cell surface markers of monocytes and lymphocytes have been examined. Combinations of pro- and anti-inflammatory biomarkers in a multi-marker panel may help identify patients who are developing severe sepsis before organ dysfunction has advanced too far. Combined with innovative approaches to treatment that target the immunosuppressive phase, these biomarkers may help to reduce the mortality rate associated with severe sepsis which, despite advances in supportive measures, remains high.

Comparison of pathogen DNA isolation methods from large volumes of whole blood to improve molecular diagnosis of bloodstream infections

For patients suffering from bloodstream infections (BSI) molecular diagnostics from whole blood holds promise to provide fast and adequate treatment. However, this approach is hampered by the need of large blood volumes. Three methods for pathogen DNA isolation from whole blood were compared, i.e. an enzymatic method (MolYsis, 1-5 ml), the novel non-enzymatic procedure (Polaris, 1-5 ml), and a method that does not entail removal of human DNA (Triton-Tris-EDTA EasyMAG, 200 µl). These methods were evaluated by processing blood spiked with 0-1000 CFU/ml of Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans. Downstream detection was performed with real-time PCR assays. Polaris and MolYsis processing followed by real-time PCRs enabled pathogen detection at clinically relevant concentrations of 1-10 CFU/ml blood. By increasing sample volumes, concurrent lower cycle threshold (Ct) values were obtained at clinically relevant pathogen concentrations, demonstrating the benefit of using larger blood volumes. A 100% detection rate at a concentration of 10 CFU/ml for all tested pathogens was obtained with the Polaris enrichment, whereas comparatively lower detection rates were measured for MolYsis (50-67%) and EasyMAG (58-79%). For the samples with a concentration of 1 CFU/ml Polaris resulted in most optimal detection rates of 70-75% (MolYsis 17-50% and TTE-EasyMAG 20-36%). The Polaris method was more reproducible, less labour intensive, and faster (45 minutes (including Qiagen DNA extraction) vs. 2 hours (MolYsis)). In conclusion, Polaris and MolYsis enrichment followed by DNA isolation and real-time PCR enables reliable and sensitive detection of bacteria and fungi from 5 ml blood. With Polaris results are available within 3 hours, showing potential for improved BSI diagnostics.

Commercial multiplex technologies for the microbiological diagnosis of sepsis

In patients with suspected sepsis, rapid and accurate diagnosis of the causative infectious agent is critical. Although clinicians often use empiric antimicrobial therapy until the blood cultures are available to potentially adjust treatment, this approach is often not optimum for patient care. Recently, several commercial molecular multiplex technologies have shown promise for fast and comprehensive diagnosis of microorganisms and their antimicrobial resistance signatures. While one class of multiplex technologies is directed at improving the speed and diagnostic information obtained from positive blood cultures, the other identifies the causative microorganisms directly from clinical blood samples. This review provides an overview of these molecular technologies and describes their performance capabilities compared to standard blood cultures and in some cases to each other. We discuss the current clinical impact, limitations, and likely futures advances these multiplex technologies may have in guiding the management of patients with sepsis.

Multiplex PCR system for rapid detection of pathogens in patients with presumed sepsis - a systemic review and meta-analysis

BACKGROUND

Blood culture is viewed as the golden standard for the diagnosis of sepsis but suffers from low sensitivity and long turnaround time. LightCycler SeptiFast (LC-SF) is a real-time multiplex polymerase chain reaction test able to detect 25 common pathogens responsible for bloodstream infections within hours. We aim to assess the accuracy of LC-SF by systematically reviewing the published studies.

METHOD

Related literature on Medline, Embase, and Cochrane databases was searched up to October 2012 for studies utilizing LC-SF to diagnose suspected sepsis and that provided sufficient data to construct two-by-two tables.

RESULTS

A total of 34 studies enrolling 6012 patients of suspected sepsis were included. The overall sensitivity and specificity for LC-SF to detect bacteremia or fungemia was 0·75 (95% CI: 0·65-0·83) and 0·92 (95%CI:0·90-0·95), respectively. LC-SF had a high positive likelihood ratio (10·10) and a moderate negative likelihood ratio (0·27). Specifically, LC-SF had a sensitivity of 0·80 (95%CI: 0·70-0·88) and a specificity of 0·95(95%CI: 0·93-0·97) for the bacteremia outcome, and a sensitivity of 0·61 (95%CI: 0·48-0·72) and a specificity of 0·99 (95%CI: 0·99-0·99) for the fungemia outcome. High heterogeneity was found in the bacteremia outcome subgroup but not in the fungemia outcome subgroup.

CONCLUSION

LC-SF is of high rule-in value for early detection of septic patients. In a population with low pretest probability, LC-SF test can still provide valuable information for ruling out bacteremia or fungemia.

Cytokines and chemokines as biomarkers of community-acquired bacterial infection

Routinely used biomarkers of bacterial etiology of infection, such as C-reactive protein and procalcitonin, have limited usefulness for evaluation of infections since their expression is enhanced by a number of different conditions. Therefore, several inflammatory cytokines and chemokines were analyzed with sera from patients hospitalized for moderate bacterial and viral infectious diseases. In total, 57 subjects were enrolled: 21 patients with community-acquired bacterial infections, 26 patients with viral infections, and 10 healthy subjects (control cohorts). The laboratory analyses were performed using Luminex technology, and the following molecules were examined: IL-1Ra, IL-2, IL-4, IL-6, IL-8, TNF-α, INF-γ, MIP-1β, and MCP-1. Bacterial etiology of infection was associated with significantly (P < 0.001) elevated serum concentrations of IL-1Ra, IL-2, IL-6, and TNF-α in comparison to levels observed in the sera of patients with viral infections. In the patients with bacterial infections, IL-1Ra and IL-8 demonstrated positive correlation with C-reactive protein, whereas, IL-1Ra, TNF-α, and MCP-1 correlated with procalcitonin. Furthermore, elevated levels of IL-1Ra, IL-6, and TNF-α decreased within 3 days of antibiotic therapy to levels observed in control subjects. The results show IL-1Ra as a potential useful biomarker of community-acquired bacterial infection.

Comparison of three different commercial PCR assays for the detection of pathogens in critically ill sepsis patients

INTRODUCTION

The high mortality rate associated with sepsis necessitates a timely identification of the causative organism in order to optimize antimicrobial therapy. PCR assays are increasingly being used for this purpose. The aim of this study was to compare three commercially available PCR systems for the diagnosis of systemic infections.

PATIENTS AND METHODS

In a prospective observational study, a broad-range (SepsiTest®; Molzym, Bremen, Germany) and two multiplex PCR assays (VYOO®; SIRS-Lab, Jena, Germany and LightCycler® SeptiFast; Roche, Mannheim, Germany) were compared to blood cultures with respect to the clinical course of 50 critically ill patients with sepsis, severe sepsis or septic shock.

RESULTS

Pathogens were detected by PCR in 12 % (SepsiTest®), 10 % (VYOO®) and 14 % (LightCycler® SeptiFast) of samples and in 26 % by blood culture. Negative results were obtained using all four methods in 32 samples (64 %) and 3 (6 %) samples were positive in all tests. Upon consideration of additional diagnostic findings and the clinical course, eight (16 %) of the positive blood culture results were deemed clinically relevant. All three PCR assays could also identify the causative organism (or a specific gene thereof) in three of these eight positive blood cultures, whereas for five of the eight, all three PCR assays were negative. In one patient with a negative blood culture, the SepsiTest®, VYOO® and LightCycler® SeptiFast assays were positive for Streptococcus species. The PCR assays appeared to be less susceptible than blood cultures to false-positive results arising from contamination with coagulase-negative staphylococcal organisms.

CONCLUSION

There was some variability between the three PCR assays tested and the corresponding blood cultures with regards to the type of pathogen detected. The three PCR assays appeared to be less susceptible to false-positive results than blood cultures.

Diagnostic performance and therapeutic impact of LightCycler SeptiFast assay in patients with suspected sepsis

Rapid and reliable identification of pathogens is very important in the management of septic patients. We retrospectively evaluated the diagnostic accuracy and clinical utility of a multiplex real-time polymerase chain reaction (PCR) assay (SeptiFast (SF)) in patients with suspected sepsis in a tertiary care hospital in Tallinn, Estonia. A total of 160 blood samples from 144 patients were included in the study. SF results were compared with corresponding blood culture (BC) results. The concordance between SF and BC was 78.8%. The rate of positive results was significantly higher in SF than in BC (33.7% vs. 21.2%, respectively; p < 0.001). A total of 27 samples were found positive by both SF and BC, 27 by SF only, and seven by BC only. Of a total of 83 microorganisms detected SF identified 71, and BC 42 (p < 0.001). SF detected markedly more patients with candidemia: 11 patients were detected by SF compared to four patients by BC. Antimicrobial treatment was changed in 21 (38.9%) of 54 SF positive cases. In conclusion, our results demonstrated the high diagnostic accuracy of SF in detection of sepsis pathogens. In conjunction with its impact on therapeutic decisions, SF proved to be a useful adjunct to conventional blood culture in the diagnosis of sepsis etiology.

New approaches to sepsis: molecular diagnostics and biomarkers

Sepsis is among the most common causes of death in hospitals. It arises from the host response to infection. Currently, diagnosis relies on nonspecific physiological criteria and culture-based pathogen detection. This results in diagnostic uncertainty, therapeutic delays, the mis- and overuse of antibiotics, and the failure to identify patients who might benefit from immunomodulatory therapies. There is a need for new sepsis biomarkers that can aid in therapeutic decision making and add information about screening, diagnosis, risk stratification, and monitoring of the response to therapy. The host response involves hundreds of mediators and single molecules, many of which have been proposed as biomarkers. It is, however, unlikely that one single biomarker is able to satisfy all the needs and expectations for sepsis research and management. Among biomarkers that are measurable by assays approved for clinical use, procalcitonin (PCT) has shown some usefulness as an infection marker and for antibiotic stewardship. Other possible new approaches consist of molecular strategies to improve pathogen detection and molecular diagnostics and prognostics based on transcriptomic, proteomic, or metabolic profiling. Novel approaches to sepsis promise to transform sepsis from a physiologic syndrome into a group of distinct biochemical disorders and help in the development of better diagnostic tools and effective adjunctive sepsis therapies.

Interpretation and Relevance of Advanced Technique Results

Advanced techniques in the field of diagnostic microbiology have made amazing progress over the past two decades due largely to a technological revolution in the molecular aspects of microbiology [1, 2]. In particular, rapid molecular methods for nucleic acid amplification and characterization combined with automation and user-friendly software have significantly broadened the diagnostic capabilities of modern clinical microbiology laboratories. Molecular methods such as nucleic acid amplification tests (NAATs) rapidly are being developed and introduced in the clinical laboratory setting. Indeed, every section of the clinical microbiology laboratory, including bacteriology, mycology, mycobacteriology, parasitology, and virology, have benefited from these advanced techniques. Because of the rapid development and adaptation of these molecular techniques, the interpretation and relevance of the results produced by such molecular methods has lagged somewhat behind. The purpose of this chapter is to review and discuss the interpretation and relevance of results produced by these advanced molecular techniques. Moreover, this chapter will address the “myths” of NAATs, as these myths can markedly influence the interpretation and relevance of these results.

Screening for bacteremia in sepsis and renal failure using hemofilters for renal replacement therapy

BACKGROUND

In patients with sepsis and renal failure, extracorporeal blood flow during renal replacement therapy may lead to the deposition of bacteria on artificial membranous surfaces, which might be suitable for the detection of pathogens. We studied whether discarded dialysis hemofilters can be used for the detection of bacteremia in patients with sepsis and renal failure.

METHODS

Hemofilters of 16 ICU patients with sepsis were sampled. The hemofilters were incubated with soy broth and dehisced under sterile conditions. Samples were plated on blood agar and analyzed. Patient's characteristics were assessed.

RESULTS

Despite the use of antibiotics in 87.5 % (14/16), a true positive detection rate of 31.3 % (5/16) for bacteremia was found by using cultures from hemofilters. The overall true positive rate of blood cultures was significantly lower (10.7 %, 8/75, p = 0.048). Bacteria detected in hemofilters were similar to those found in blood cultures or by cultures from other sources of infection in 80 % (4/5).

CONCLUSIONS

Cultures from used hemofilters of patients with sepsis and renal failure provide the opportunity to identify pathogenic microorganisms as an add-on approach. Further studies should investigate whether this method is applicable in clinical practice to enhance the sensitivity of microbiological diagnostics.

Microbial diagnostics in patients with presumed severe infection in the emergency department

INTRODUCTION

Sepsis in the early stage is a common disease in emergency medicine, and rapid diagnosis is essential. Our aim was to compare pathogen diagnosis using blood cultures (BC) and the multiplex polymerase chain reaction (PCR) test.Methods. At total of 211 patients admitted to the multidisciplinary emergency department of our university hospital between 2006 and 2009 with suspected severe infection from any origin were studied. Blood samples for BC (aerobic and anaerobic) and multiplex PCR were taken for identification of infectious microorganisms immediately after hospital admission. Results of the BC and PCR correlated with procalcitonin concentration (PCT) and clinical diagnosis of sepsis (≥2 positive SIRS criteria) as well as with severity of disease at admission and with clinical outcome measures.

RESULTS

Results of the BC were available in 200 patients (94.8%) and PCR were available in 119 patients (56.3%), respectively. In total, 87 BC (43.5%) were positive and identified 94 pathogens. In 45 positive PCRs, 47 pathogens (37.8%) were found. Identical results were obtained in 81.4%. In addition, BC identified 9 Gram-positive and 3 Gram-negative bacteria, while PCR added 5 Gram-negative pathogens. Coagulase-negative staphylococci were detected in blood cultures only (n=20, 21.3%), whereas PCR identified significantly more Gram-negative bacteria than BC. In patients with positive PCR results, the PCT level was significantly higher than in patients with negative PCR (15.0±23.3 vs. 8.8±32.8 ng/ml, p<0.001). This difference was not observed for BC (10.6±25.7 vs. 11.6±44.9 ng/ml, p=0.075). The APACHE II score correlated with PCR (19.2±9.1 vs. 15.8±8.9, p<0.05) and was also higher in positive BC (18.7±8.7 vs. 14.4±8.0, p<0.01). Positive PCR and BC were correlated with negative clinical outcomes (e.g., transfer to ICU, mechanical ventilation, renal replacement therapy, death).

CONCLUSION

In patients admitted with suspected severe infection, a high percentage of positive BC and PCR were observed. Positive findings in the PCR correlate with elevated levels of PCT and high APACHE II scores.

Routine use of a real-time polymerase chain reaction method for detection of bloodstream infections in neutropaenic patients

We examined the performance of a real-time polymerase chain reaction (PCR) test (SeptiFast) for early detection of bloodstream infection in febrile neutropaenic patients. Blood samples from 201 patients were screened for pathogens by blood culture and by PCR on the first day of fever. PCR results were available earlier (median 3 days for bacteria, 5 days fungal pathogens; P ≤ 0.01). The sensitivity (0.74) and specificity (0.96) of the PCR test were acceptable for Gram negatives when culture was considered the gold standard, but sensitivity of the test was poorer for Gram-positive organisms (0.39). The PCR assay also led to 22.9% of invalid results. SeptiFast speeds the microbiological diagnosis of bloodstream infection in neutropaenic patients. However, the frequent failure of instrumental control procedures, the relatively poor sensitivity of the test, and the lack of phenotypic data on antimicrobial susceptibility associated with its high costs suggest that this assay cannot replace the blood cultures.

Antimicrobial use in the ICU: indications and accuracy--an observational trial

BACKGROUND

In intensive care unit (ICU) patients, signs of infection and inflammation are similar, making diagnosis of bacterial infections difficult. Antimicrobials may therefore be overused, contributing to development of antimicrobial-resistant bacteria.

OBJECTIVES

To measure the accuracy of clinician decisions to start antimicrobials; to correlate clinician certainty with the presence of infection; and to examine whether physiological variables correlate with clinician certainty.

DESIGN

Prospective observational study.

SETTING AND PATIENTS

Patients staying >48 hours in a general ICU of a tertiary care hospital.

MEASUREMENTS

The ICU clinician's certainty for the presence of infection was recorded when starting antimicrobials. An independent infectious diseases (ID) specialist determined if antimicrobials were required and if infection was present. Clinician antibiotic start decisions were tested for accuracy according to the ID determination for the presence of infection.

RESULTS

Empirical antimicrobial therapy was justified by the presence of infection on 67/125 (54%) occasions. Clinician certainty for infection correlated well with the presence of defined infection (r(2) = 0.78), however, infection was defined on 6/19 (31%) occasions when ICU clinician certainty was low (≤2), and antimicrobials were prescribed even when clinician certainty was minimal. Antimicrobial course length was similar whether infection was defined or not (11.5 ± 9.2 vs 10.7 ± 9.1 days; P = 0.65). Physiological variables were not associated with clinician certainty of infection.

CONCLUSIONS

Antimicrobial therapy is probably overused in the ICU, possibly resulting from difficulties in diagnosis and the perceived greater risk of untreated infection when compared to the risks of potentially unnecessary antimicrobial therapy. Efforts to improve antimicrobial-related decision-making should be mandatory.

Evaluation of a polymerase chain reaction assay for pathogen detection in septic patients under routine condition: an observational study

Background

Treatment of septic shock relies on appropriate antimicrobial therapy. Current culture based methods deliver final results after days, which may delay potentially lifesaving adjustments in antimicrobial therapy. This study was undertaken to compare PCR with blood culture results under routine conditions regarding 1. impact on antimicrobial therapy, and 2. time to result, in patients with presumed sepsis.

Methodology/Principal Findings

This was an observational study in a 50 beds ICU of a university hospital. In 245 patients with suspected sepsis, 311 concomitant blood cultures and blood for multiplex PCR (VYOO®) were obtained. 45 of 311 blood cultures (14.5%) and 94 of 311 PCRs (30.1%) were positive. However, blood culture or microbiological sampling from the presumed site of infection rarely confirmed PCR results and vice versa. Median time to positivity and interquartile range were 24.2 (18.0, 27.5) hours for the PCR and 68 (52.2, 88.5) hours for BC (p<0.01). PCR median time to result was dependent on technician availability (53.5 hours on Saturdays, 7.2 hours under optimal logistic conditions). PCR results showed good correlation with procalcitonin (p<0.001). In 34% of patients with positive PCRs antimicrobial therapy was considered inadequate according to assessment of clinical arbitrators including 5 patients with vancomycin-resistant enterococci (VRE), 3 cases with multiresistant staphylococci, and 4 patients with fungi.

Conclusions

The results of this observational study support the hypothesis that PCR results are available faster, are more frequently positive, and may result in earlier adjustment of antimicrobial therapy. However, shorter time to result can only be fully exploited when the laboratory is adequately staffed for a 24 hour/7 day service, or when point of care/automated assay systems become available.

Attributable costs of patients with candidemia and potential implications of polymerase chain reaction-based pathogen detection on antifungal therapy in patients with sepsis

PURPOSE

The purposes of this study were to calculate attributable costs of candidemia in patients with severe sepsis and to obtain preliminary data regarding the potential effects of polymerase chain reaction-based pathogen detection on antifungal therapy for these patients.

METHODS

Patients treated between 2004 and 2010 because of severe sepsis were included into this retrospective analysis. The hospital management provided annual fixed costs per patient-day; data for variable intensive care unit costs were taken from the literature. Multiplex polymerase chain reaction (PCR) was used (VYOO, SIRS-Lab, Jena, Germany) for pathogen detection in the blood.

RESULTS

Thirty-two patients with candidemia were identified. Of 874 patients with sepsis, propensity score matching found 32 corresponding patients with sepsis but without candida infection but similar risk factors for developing candidemia. Attributable costs of candidemia were 7713.79 Euro (cost increase, 19.4%). Initiation of antifungal therapy was reduced from 67.5 (52.4, 90) hours in the group, where candida infection was determined by blood culture, to 31.0 (28.0, 37.5; P < .01) hours after detection by multiplex PCR.

CONCLUSIONS

Candidemia increases costs of care in patients with septic shock. Polymerase chain reaction-based pathogen detection significantly reduces the time to initiation of antifungal therapy. This might impact on the clinical course of the disease but need to be confirmed in further trials.

Predictors of survival in sepsis: what is the best inflammatory marker to measure?

PURPOSE OF REVIEW

Sepsis is relevant due to its high morbidity and mortality. For both sepsis diagnosis and outcome prediction many biomarkers have been described in the literature. Most of these markers are objects of scientific interest rather than being introduced into daily clinical practice. However, due to their unspecific character and their insufficient predictive value for the individual person, research focus is still on new aspects in sepsis-related biomarkers.

RECENT FINDINGS

Beyond the widely used acute-phase proteins C-reactive protein (CRP) and procalcitonin (PCT), many new molecules have been studied deriving from different organs or cells affected, due to the systemic nature of sepsis. Cytokines, coagulation factors/characteristics, vasoactive hormones, and several others have been recently proved to be relevant in sepsis syndrome and probably useful for outcome prediction. However, single time point measurements may be less predictive than consideration of the time-dependent course of parameters. Clinical decision just based on a biomarker is still not feasible because of the huge inter-individual differences in the inflammatory response.

SUMMARY

Many biomarkers display relevant correlation with the clinical outcome of patients with severe sepsis and septic shock. Consideration of their time courses may be more reliable than absolute levels. Clinical decision should not be based only on biomarkers but organ dysfunctions, for example, should also be taken into account.

Diagnostic utility of LightCycler SeptiFast and procalcitonin assays in the diagnosis of bloodstream infection in immunocompromised patients

Sepsis is an increasingly prevalent cause of death, and management in the early stage is a critical issue. However, microbiological findings are generally obtained late during the course of the disease. In this study, we evaluated the clinical utility of procalcitonin (PCT) in improving the diagnosis of bloodstream infections and the potential utility of the SeptiFast (SF) test, a multiplex pathogen detection system, in the etiological diagnosis of immunocompromised patients. Seventy-nine hospitalized immunocompromised patients were included in this study. Our results demonstrate that while the PCT value correlates highly with sepsis, the results do not discriminate adequately enough to justify its independent use as a diagnostic tool. The SF test, combined with blood cultures, improves microbiological data in immunocompromised patients, especially in cases of previous antibiotic therapy and invasive fungal infection.

Would earlier microbe identification alter antibiotic therapy in bacteremic emergency department patients?

BACKGROUND

Although debate exists about the treatment of sepsis, few disagree about the benefits of early, appropriately targeted antibiotic administration.

STUDY OBJECTIVES

To determine the appropriateness of empiric antimicrobial therapy and the extent to which therapy would be altered if the causative organism for sepsis was known at the time of administration.

METHODS

This was a retrospective cohort study, conducted in an academic Emergency Department (ED), on consecutive positive blood cultures between November 1, 2008 and February 1, 2009. Blood cultures and the appropriateness of administered antimicrobial therapy were evaluated. Therapy choices were categorized based on whether or not a physician, complying with antimicrobial guidelines, would have made changes to empiric antibiotic therapy had the causative organism initially been known.

RESULTS

There were 90 positive blood cultures obtained from 84 patients. Of these, 21.1% (n=19) were considered contaminants. The final categorization of empiric antibiotics given in the ED for the remaining blood culture results were: 1) therapy would be changed to narrower-spectrum antibiotics (n=34, 55.7%); 2) therapy would be changed because the organism was not covered (n=13, 21.3%); and 3) therapy would remain the same (n=14, 23.0%). There was 90.2% inter-rater agreement for these classifications (p<0.0001), with a kappa of 0.84. Polymerase chain reaction analysis had a statistically significant advantage (p<0.0001) over Infectious Disease Society of America protocols in facilitating accurate antimicrobial therapies.

CONCLUSION

This study confirms the need for more rapid and accurate laboratory methods for bloodstream pathogen identification.

Improvement of detection of bacterial pathogens in normally sterile body sites with a focus on orthopedic samples by use of a commercial 16S rRNA broad-range PCR and sequence analysis

A new commercially available universal 16S and 18S rRNA gene PCR test, which is followed by sequence analysis of amplicons (SepsiTest), was evaluated for rapid identification of pathogens in the diagnosis of bone and joint infections. Eighty-three orthopedic samples and 21 specimens from other normally sterile body sites collected from 84 patients were analyzed in parallel by culture and PCR for detection of bacteria and fungi. Compared to culture, the diagnostic sensitivity and specificity of PCR were 88.5% and 83.5%, respectively. The detection rate of PCR (34.6%) was higher than that of bacterial culture (25.0%) as a consequence of the presence of fastidious and noncultivable species in samples and antibiotic treatment of patients. Thirteen culture-negative infections were identified by PCR, and PCR was able to detect culture-proven polymicrobial infections. On the other hand, three samples were culture positive but PCR negative. SepsiTest was demonstrated to be a valuable supplemental tool in the rapid detection of bacteria, especially for fastidious and noncultivable organisms, allowing earlier initiation of pathogen-adapted therapy in patients with bone and joint infections.

Classification of sepsis, severe sepsis and septic shock: the impact of minor variations in data capture and definition of SIRS criteria

PURPOSE

To quantify the effects of minor variations in the definition and measurement of systemic inflammatory response syndrome (SIRS) criteria and organ failure on the observed incidences of sepsis, severe sepsis and septic shock.

METHODS

We conducted a prospective, observational study in a tertiary intensive care unit in The Netherlands between January 2009 and October 2010. A total of 1,072 consecutive adults were included. We determined the upper and lower limits of the measured incidence of sepsis by evaluating the influence of the use of an automated versus a manual method of data collection, and variations in the number of SIRS criteria, concurrency of SIRS criteria, and duration of abnormal values required to make a particular diagnosis.

RESULTS

The measured incidence of SIRS varied from 49% (most restrictive setting) to 99% (most liberal setting). Subsequently, the incidences of sepsis, severe sepsis and septic shock ranged from 22 to 31%, from 6 to 27% and from 4 to 9% for the most restrictive versus the most liberal measurement settings, respectively. In non-infected patients, 39-98% of patients had SIRS, whereas still 17-6% of patients without SIRS had an infection.

CONCLUSIONS

The apparent incidence of sepsis heavily depends on minor variations in the definition of SIRS and mode of data recording. As a consequence, the current consensus criteria do not ensure uniform recruitment of patients into sepsis trials.

Multiplex PCR for rapid and improved diagnosis of bloodstream infections in liver transplant recipients

This prospective study evaluated the utility of the SeptiFast (SF) test in detecting 25 clinically important pathogens in 225 blood samples from 170 intensive care unit (ICU) patients with suspected sepsis after liver transplantation (LTX) or after other major abdominal surgery (non-LTX). SF yielded a significantly higher positivity rate in the LTX group (52.3%) than in the non-LTX group (30.5%; P = 0.0009). SF may be a powerful tool for the early diagnosis of bloodstream infections in LTX patients.

Molecular diagnosis of sepsis

INTRODUCTION

Current management of sepsis relies on the early detection and early administration of antimicrobials. This requires detection of pathogens earlier than conventional blood cultures and recognition of the immune status of the host earlier than the conventional biomarkers. This can be achieved by molecular techniques.

AREAS COVERED

Molecular diagnosis of pathogens is based on either rapid detection of pathogens grown in blood cultures or direct use of whole blood and blood products. Molecular diagnosis of the constellation of activations and inhibitions of pathways implicated in cellular processes can be achieved by gene profiling of a large array of genes.

EXPERT OPINION

Molecular microbial diagnosis enables rapid identification and precedes results obtained by conventional culture methods. Its role can be proved more useful in sepsis caused by specific microorganisms such as fungi performed by PMA-FISH and MALDI-TOF MS. Molecular techniques using blood aim for rapid pathogen identification. However, the provided information regarding the antimicrobial susceptibility of the pathogen is limited. Gene profiling in sepsis provides individualized information for the activation or inhibition of pathways of a variety of cellular processes. The transcriptome information is difficult to interpret in everyday clinical practice particularly on how information translates to patient needs.

Current management of sepsis in critically ill adult patients

Severe sepsis is a common occurrence in critically ill patients and a major cause of morbidity and mortality in this population. Management relies on the early identification and treatment of the underlying causative infection, adequate and rapid hemodynamic resuscitation, support of associated organ failure and modulation of the immune response with drotrecogin alfa (activated) when it is not contraindicated, and corticosteroids in severe septic shock. We will review current approaches to each of these categories.

Quantitative rt-PCR holds promise as a screening tool for patients with severe sepsis

OBJECTIVE

The aim of the present study was to determine if the quantification of bacterial 16S rDNA could be clinically useful in predicting patients at increased risk of developing septic shock.

METHODS

A retrospective study of patients with positive blood cultures taken on arrival to the ED. An EDTA sample was collected simultaneously with blood cultures and assayed by polymerase chain reaction to quantitate the bacterial 16S rDNA load. Descriptive and clinical data were collected from the medical record and this was blinded to the 16S rDNA result. Subsequently, the 16S rDNA result was compared with illness severity markers including septic shock and death to determine the relationship between the 16S rDNA load and illness severity.

RESULTS

98 patients (mean age 61 ± 20 years, range 18-92) with positive blood cultures were studied, most commonly growing Escherichia coli (n= 25) and Staphylococcus aureus (n= 23). 16 (16%) died. There were 42 (43%) 16S rDNA positive patients. A high 16S rDNA load was associated with an increased risk of developing delayed septic shock (OR 21.9, 95% CI 2.5-192.6) in comparison with either a low or negative 16S rDNA load; with a mortality OR 4.6 (95% CI 0.9-23.5).

CONCLUSIONS

The quantitative assay for 16S rDNA might be a useful screening tool to detect severe sepsis in those whom it might not be clinically suspected. However, prospective studies are required to further assess the clinical usefulness of this assay.

Performance of the LightCycler SeptiFast test Mgrade in detecting microbial pathogens in purulent fluids

The performance of the LightCycler SeptiFast (SF) assay was compared to that of culture methods in the detection of microorganisms in 43 purulent fluids from patients with pyogenic infections. The SF assay was more sensitive than the culture methods (86% versus 61%, respectively), irrespective of whether the infections were mono- or polymicrobial.

Diagnostic accuracy and potential clinical value of the LightCycler SeptiFast assay in the management of bloodstream infections occurring in neutropenic and critically ill patients

OBJECTIVES

The objectives of this study were to compare the performance of the LightCycler SeptiFast Test MGRADE and conventional blood culture in the etiological diagnosis of febrile episodes occurring in neutropenic and critically ill patients (in the intensive care unit; ICU), and to assess the potential clinical value of the SeptiFast test in patient management.

METHODS

A total of 86 febrile episodes occurring in 33 neutropenic patients and 53 ICU patients were analyzed. Blood samples for blood culture and SeptiFast testing were obtained at the onset of fever, before the implementation of empirical antimicrobial therapy.

RESULTS

The overall microorganism-to-isolate agreement between the SeptiFast test and blood culture was 69% (κ=0.37) in neutropenic patients and 75% (κ=0.56) in ICU patients. The sensitivity of the SeptiFast assay for clinically relevant episodes of bacteremia and fungemia was 62% in neutropenic patients and 70% in ICU patients. Based on SeptiFast results, empirical treatments were deemed adequate in all but one of the febrile episodes. Nevertheless, early antibiotic treatment readjustment was judged feasible in most of clinically significant episodes overall.

CONCLUSIONS

The SeptiFast assay is a valuable ancillary method for the diagnosis of bloodstream infections in neutropenic and ICU patients. In these clinical settings, results of the SeptiFast assay may lead to a more targeted antibiotic therapy early after the onset of fever.

Nosocomial methicillin-resistant Staphylococcus aureus (MRSA) pneumonia: linezolid or vancomycin? - Comparison of pharmacology and clinical efficacy

The incidence of nosocomial pneumonia involving methicillin-resistant Staphylococcus aureus strains (MRSA) is on the rise worldwide. For years, vancomycin has been used as the drug of choice in the treatment of MRSA infections and was recommended as such by clinical guidelines. There is growing evidence that vancomycin, despite low resistance rates is a suboptimal therapeutic option in critically ill patients, particularly in patients with pneumonia. Disadvantages of vancomycin are i) slow bactericide action, ii) poor penetration into pulmonary tissue, iii) the globally slowly increasing vancomycin MICs ("creep") that result in increased clinical failure despite being susceptible according to defined break points and iv) nephrotoxicity. In contrast to other novel antibiotics with MRSA activity, Linezolid is currently approved for the treatment of nosocomial pneumonia in the USA and Europe. Several studies have compared vancomycin with linezolid for nosocomial pneumonia with conflicting results. This review compares both substances regarding pharmacodynamics, resistance, safety and clinical efficacy and discusses preliminary data of the ZEPHyR study. This study compared linezolid versus vancomycin in patients with proven MRSA pneumonia and was the largest trial ever conducted in this population.

We should be measuring genomic bacterial load and virulence factors

OBJECTIVE

To describe relevant pathogen-related characteristics and their impact on sepsis pathogenesis and prognosis.

DATA SOURCE

Current literature regarding genomic bacterial load and virulence factors, with an emphasis on the impact of these factors on pathophysiology and prognosis of sepsis.

DATA EXTRACTION AND SYNTHESIS

The current paradigm on sepsis pathophysiology and management overlooks aspects concerning the nature and characteristics of the infecting pathogen. Our findings suggest that evaluation of genomic bacterial load might be useful to assess severity and predict prognosis in septic patients; its use during treatment for monitoring clinical response is another interesting potential application. Virulence factors identification might help to develop pathogen-specific therapeutic strategies for higher-risk septic patients.

CONCLUSIONS

The recognition of the importance of quantifying the pathogen has major clinical implications and will open up a new field of exploration of therapies targeted at anticipating development and appropriate treatment in severe sepsis. The improved detection and understanding of bacterial virulence factors may lead to specific therapies.

Minimally Invasive Diagnostic Strategy in Immunocompromised Patients with Pulmonary Infiltrates

Acute respiratory failure (ARF) is the main reason for ICU admission in patients with haematological malignancies. High mortality rates of up to 50% are reported in this situation, and mortality is highest when mechanical ventilation is needed. Rapid and accurate diagnostic methods are needed in these vulnerable patients to ensure the prompt initiation of effective treatment. However, the broad array of possible cause of ARF raises diagnostic challenges. In this review, we discuss the DIRECT strategy, which identifies the most plausible diagnosis in each patient based on the type of immune deficiency and clinical presentation. We will focus on non-invasive laboratory tests developed in recent years, discussing their sensitivity and specificity. We also discuss the usefulness in cancer patients with specific organ dysfunctions of biomarkers introduced over the past few years.

Conventional and molecular techniques for the early diagnosis of bacteraemia

Bloodstream infections account for 30-40% of all cases of severe sepsis and septic shock, and are major causes of morbidity and mortality. Diagnosis of bloodstream infections must be performed promptly so that adequate antimicrobial therapy can be started and patient outcome improved. An ideal diagnostic technology would identify the infecting organism(s) and their determinants of antibiotic resistance, in a timely manner, so that appropriate pathogen-driven therapy could begin promptly. Unfortunately, despite the essential information it provides, blood culture, the gold standard, largely fails in this purpose because time is lost waiting for bacterial or fungal growth. Several efforts have been made to optimise the performance of blood culture, such as the development of technologies to obtain rapid detection of microorganism(s) directly in blood samples or in a positive blood culture. The ideal molecular method would analyse a patient's blood sample and provide all the information needed to immediately direct optimal antimicrobial therapy for bacterial or fungal infections. Furthermore, it would provide data to assess the effectiveness of the therapy by measuring the clearance of microbial nucleic acids from the blood over time. None of the currently available molecular methods is sufficiently rapid, accurate or informative to achieve this. This review examines the principal advantages and limitations of some traditional and molecular methods commercially available to help the microbiologist and the clinician in the management of bloodstream infections.