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

Emerging Technologies for Molecular Diagnosis of Sepsis

Rapid and accurate profiling of infection-causing pathogens remains a significant challenge in modern health care. Despite advances in molecular diagnostic techniques, blood culture analysis remains the gold standard for diagnosing sepsis. However, this method is too slow and cumbersome to significantly influence the initial management of patients. The swift initiation of precise and targeted antibiotic therapies depends on the ability of a sepsis diagnostic test to capture clinically relevant organisms along with antimicrobial resistance within 1 to 3 h. The administration of appropriate, narrow-spectrum antibiotics demands that such a test be extremely sensitive with a high negative predictive value. In addition, it should utilize small sample volumes and detect polymicrobial infections and contaminants. All of this must be accomplished with a platform that is easily integrated into the clinical workflow. In this review, we outline the limitations of routine blood culture testing and discuss how emerging sepsis technologies are converging on the characteristics of the ideal sepsis diagnostic test. We include seven molecular technologies that have been validated on clinical blood specimens or mock samples using human blood. In addition, we discuss advances in machine learning technologies that use electronic medical record data to provide contextual evaluation support for clinical decision-making.

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.

Diagnostic accuracy of SeptiFast multi-pathogen real-time PCR in the setting of suspected healthcare-associated bloodstream infection

PURPOSE

SeptiFast is a real-time PCR assay which targets ribosomal DNA sequences of bacteria and fungi, enabling detection and identification of the commonest pathogens in blood within a few hours, including those acquired in healthcare settings. We report here the first detailed assessment of SeptiFast that focuses on healthcare-associated bloodstream infections which develop during routine critical care.

METHODS

This was a prospective multicentre study designed to compare the clinical diagnostic accuracy of SeptiFast versus microbiological culture and independent clinical adjudication. This Phase III diagnostic study was performed in an adequately sized cohort of adult patients who developed new signs of suspected bloodstream infection while receiving routine critical care.

RESULTS

Of 1,006 new episodes of suspected bloodstream infection in 853 patients, 922 (92 %) of these episodes in 795 patients met the inclusion criteria of the study. Patients had been exposed to a median of 8 days (interquartile range 4-16) of hospital care and had received high levels of organ support and recent antibiotic exposure. The SeptiFast test, when compared with bloodstream infection at the species/genus level, had a greater specificity [0.86, 95 % confidence interval (CI) 0.83-0.88] than sensitivity (0.50, 95 % CI 0.39-0.61). There was a low prevalence of blood culture-proven pathogens (9.2 %, 95 % CI 7.4-11.2 %), and the post-test probabilities of both a positive (26.3 %, 95 % CI 19.8-33.7 %) and a negative SeptiFast test (5.6 %, 95 % CI 4.1-7.4 %) indicated potential limitations of this technology in diagnosing bloodstream infection.

CONCLUSION

When compared with blood culture, SeptiFast is likely to have limited utility for the diagnosis of healthcare-associated bloodstream infection in critical care patients despite its potential to deliver results more rapidly.

[Indocyanine green elimination for the evaluation of liver function: prognostic value in patients with community-acquired sepsis]

BACKGROUND

The aim of our clinical study was to correlate liver function measured by indocyanine green (ICG) elimination and clinical outcomes in patients with an early stage of community-acquired sepsis (CAS).

MATERIALS AND METHODS

A total of 341 patients (≥ 18 years) presenting with suspicion of CAS or evidence of an infection and fulfillment of ≥ 2 systemic inflammatory response syndrome (SIRS) criteria were included in the observational study"Prognosis of early sepsis 2" (Prognose der frühen Sepsis 2, ProFS 2). Patients who had been hospitalized within the last 7 days were excluded. In a subgroup of these patients (n = 72) who were transferred to an intensive or intermediate care unit according to the clinical judgment of the treating physicians, ICG elimination (plasma disappearance rate, ICG-PDR; 15 min retention rate, ICG-R15) was assessed by using a noninvasive monitoring system (LiMON, PULSION Medical Systems, Germany). ICG-PDR and -R15 were determined on the day of admission (n = 72) and after 96 h (n = 34). The primary end point of the study was defined as death within 30 days. Secondary endpoints were need for renal replacement therapy, requirement for invasive mechanical ventilation, and length of stay in an intermediate or intensive care unit.

RESULTS AND CONCLUSION

In contrast to patients with sepsis or severe sepsis, ICG elimination was found to be significantly impaired in patients with septic shock. Furthermore, a significant predictive value of ICG-PDR and -R15 on the day of admission for the need for subsequent renal replacement therapy (n = 12) was observed. In addition, reduced ICG elimination was associated with a longer stay in an intermediate or intensive care unit. However, ICG elimination on admission could not predict 30-day mortality (n = 14) or requirement of mechanical ventilation (n = 20).

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.

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.

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.

APACHE II scoring to predict outcome in post-cardiac arrest

INTRODUCTION

Despite advancements in management of cardiac arrest, mortality remains high and few severity of illness scoring systems have been calibrated in this population. The goal of the current investigation was to assess the Acute Physiology and Chronic Health Evaluation II score in post-cardiac arrest.

MEASUREMENTS

This is a prospective observational study of adult post-cardiac arrest patients at a tertiary-care center. The primary outcome variable was in-hospital mortality and secondary outcome variable was neurologic outcome. APACHE II scores were used to predict outcomes using logistic modeling.

MAIN RESULTS

A total of 228 subjects were included in the analysis. The median age of the cohort was 70 (IQR: 64-71) and 32% (72/228) of the patients were female. The median downtime was 15 min (IQR: 7-27) and initial lactate 5.9 mmol/L (IQR: 3.5-8.4). 71 (57%) of deaths occurred prior to the 72-h follow-up and overall in-hospital mortality was 55% (125/228). Discrimination of APACHE II score in all cardiac arrest patients increased in stepwise fashion from 0-h to 72-h follow-up (AUC: 0-h: 0.62; 24-h: 0.75; 48-h: 0.82; 72-h: 0.86).

CONCLUSIONS

APACHE II score is a poor predictor of outcome at time zero for out-of-hospital cardiac arrest (OHCA) post-arrest patients consistent with the original development of the score in the critically ill. For in-hospital cardiac arrest (IHCA) at time zero and for both IHCA and OHCA at 24h and beyond, the APACHE II score was a modest indicator of illness severity and predictor of mortality/neurologic morbidity.

Outcome prediction using clinical scores and biomarkers in patients with presumed severe infection in the emergency department

BACKGROUND

Severe infections play an important role in the emergency department (ED) and early risk stratification is essential. We compared the prognostic value of APACHE II, SOFA, and MEDS scores, and the biomarkers C-reactive protein (CRP), procalcitonin (PCT), and interleukin 6 (IL-6).

METHODS

We performed a prospective observational study. Patients aged 18 years or older with a severe infection, from whom blood cultures were taken, were included.

RESULTS

Two hundred and eleven patients were included. The 30-day mortality rate was 8.5%. All scores and biomarkers showed significant area under the curve (AUC) values of receiver operating characteristic curve analysis for death within 30 days: 0.801 for APACHE II, 0.785 for MEDS, 0.708 for SOFA, 0.693 for CRP, 0.651 for PCT, and 0.716 for IL-6. For treatment in an ICU and need for mechanical ventilation, these parameters had significant AUC values, too. For renal replacement therapy, only APACHE II, SOFA, and PCT showed significant AUC values. According to the trend observed, the AUC values were highest for the APACHE II score.

CONCLUSIONS

All investigated parameters have a predictive value in patients with an infection in the ED. According to the trend observed, the APACHE II score seems to have the best discriminative power. Use of the APACHE II score already at the time of admission to the ED may be useful for stratifying patients at risk for ICU treatment, thereby using the same score in the ED and the ICU.