Defining the epidemiology of bloodstream infections: the 'gold standard' of population-based assessment

Mitochondria sense bacterial lactate and drive release of neutrophil extracellular traps

Neutrophils induce oxidative stress, creating a harsh phagosomal environment. However, Staphylococcus aureus can survive these conditions, requiring neutrophils to deploy mechanisms that sense bacterial persistence. We find that staphylococcal lactate is a metabolic danger signal that triggers neutrophil extracellular trap release (NETosis). Neutrophils coordinate mitochondria in proximity to S. aureus-containing phagosomes, allowing transfer of staphylococcal lactate to mitochondria where it is rapidly converted into pyruvate and causes mitochondrial reactive oxygen species, a precursor to NETosis. Similar results were observed in response to phylogenetically distinct bacteria, implicating lactate accumulation as a broad signal triggering NETosis. Furthermore, patients with systemic lupus erythematosus (SLE) are more susceptible to bacterial infections. We find that SLE neutrophils cannot sense bacterial lactate impairing their capacity to undergo NETosis upon S. aureus infection but initiate aberrant NETosis triggered by apoptotic debris. Thus, neutrophils adapt mitochondria as sensory organelles that detect bacterial metabolic activity and dictate downstream antibacterial processes.

Community-onset bloodstream infection among people with opioid use disorders: a twenty-year population-based cohort study in Queensland, Australia

BACKGROUND

Few studies have examined infection risk related to opioid misuse in non-selected populations.

OBJECTIVES

We sought to identify clinical factors and outcomes among adults with opioid use disorder-associated bloodstream infections (BSI)in Queensland, Australia.

METHODS

All Queensland residents aged ≥20 years with incident community-onset BSI hospitalised within the public healthcare system during 2000-2019 were included. Patients with opioid use disorders were identified and clinical and outcome information obtained using state-wide databases.

RESULTS

77,392 community-onset BSIs occurred among 66,424 individuals of which 828 (1.3%) patients were diagnosed with an opioid use disorder. Subjects with opioid use disorders were younger and less likely to have healthcare-associated infections. While the prevalence of nearly all co-morbidities evaluated was higher among subjects without opioid use disorders, patients with opioid use disorders were six times more likely to have liver disease. Endocarditis was eight times more likely among subjects with opioid use disorders, and these patients were more likely to be infected with Staphylococcus aureus and/or yeasts, and less likely Escherichia coli as compared to those without opioid use disorders. The median hospital stays were 18 and 8 days and crude all cause 30-day case-fatality was 5.1% versus 11.4% for those with and without opioid use disorders, respectively (p < 0.001 for each). After adjusting for confounding variables, an opioid use disorder was not associated with increased risk for death (adjusted odds ratio; 1.0; 95% confidence interval, 0.7-1.4; p = 0.9).

CONCLUSION

Opioid use disorders are potentially modifiable conditions that are associated with a major burden of BSI-related disease.

Incidence and resistance rates of Pseudomonas aeruginosa bloodstream infections in Switzerland: a nationwide surveillance study (2010-2022)

PURPOSE

Bloodstream infections (BSIs) cause significant morbidity and mortality worldwide. Pseudomonas aeruginosa is an important microorganism in BSIs. The aim of this study was to analyze recent trends in the incidence and resistance rates of P. aeruginosa BSIs in Switzerland and its different linguistic regions.

METHODS

This retrospective, nationwide observational study analyzed the incidence (using Poisson regression models) and antimicrobial resistance (using logistic regression models) of P. aeruginosa BSIs in Switzerland from 2010 to 2022.

RESULTS

The annual incidence of P. aeruginosa BSIs in Switzerland increased from 5.5 BSIs per 100,000 inhabitants in 2010 to 7.6 BSIs per 100,000 inhabitants in 2022 (p < 0.001). The incidence was higher in the French-speaking region than in the German-speaking region. The resistance rates increased significantly for cefepime (2.4% in 2010, 8.8% in 2022; p < 0.001), ceftazidime (5.6% in 2010, 9.4% in 2022; p = 0.014), ciprofloxacin (3.3% in 2010, 6.5% in 2022; p = 0.014), and piperacillin-tazobactam (6.4% in 2010, 11.2% in 2022; p = 0.002). No significant trends were observed for carbapenem-, aminoglycoside-, or multidrug-resistant P. aeruginosa. A high incidence was observed in patients ≥ 80 years, whereas resistance rates were high in young patients.

CONCLUSION

The increase in the incidence of P. aeruginosa BSIs emphasizes the importance of monitoring resistant and susceptible P. aeruginosa BSIs. Compared to the population-weighted mean resistance rates in Europe in 2022, those in Switzerland were lower, but an increase was observed for most antibiotics. The high resistance rates in young patients require further investigation.

The Etiology of Bloodstream Infections at an Italian Pediatric Tertiary Care Hospital: A 17-Year-Long Series

Knowledge of epidemiology is essential for guiding correct antibiotic prescription, reducing bacteremia-associated mortality, and implementing targeted infection control programs. However, only a few studies have reported on the epidemiology of bloodstream infections (BSIs) in pediatrics. We performed a retrospective analysis of all BSIs (excluding those caused by common skin contaminants) diagnosed from 2006 to 2022 in patients younger than 18 years who were treated at an Italian pediatric tertiary care hospital. Overall, 2395 BSIs were recorded, including 2207 (92.15%) due to bacteria and 188 (7.85%) due to fungi. The incidence rate (BSIs/10,000 hospital discharges, IR) of bacterial BSIs significantly increased during the study period. In particular, BSIs caused by S. aureus (including MRSA), Enterobacterales (including ESBL and AmpC producers), Enterococcus spp., and P. aeruginosa became more common. The frequency of carbapenem-resistant strains was <1% and stable over time. Conversely, there was a significant reduction in the incidence of BSIs due to S. pneumoniae. The BSIs were stratified by patient age, and S. aureus was the most frequent cause of BSIs in all age groups, while E. coli was the most frequent in the Enterobacterales family. S. agalactiae was the third most frequent cause of neonatal early-onset BSIs. The prevalence of Enterococcus spp. increased in the subgroups from 8 days to 5 years of age, while P. aeruginosa became more prevalent in children over 5 years of age. S. aureus was also the most frequent isolate in both community- and hospital-onset BSIs, followed by E. coli. The prevalence of multidrug-resistant (MDR) pathogens was very low. It was <5% for both Gram-positive (i.e., MRSA and VRE) and Gram-negative (ESBL, AmpC, and carbapenem-resistant) pathogens, and MDR pathogens were almost exclusively detected in hospital-onset BSIs. Fungi accounted for just under 8% of BSIs. C. albicans was the most frequently isolated strain, followed by C. parapsilosis. Notably, the IR of fungemia did not change significantly during the study period, in spite of an increase in the absolute number of events. The continuous monitoring of local epidemiology is essential to identify changes in the IRs of pathogens and antibiotic susceptibility and to guide antibiotic treatments, especially in the phase when antibiograms are not yet available.

The scope of the antimicrobial resistance challenge

Each year, an estimated 7·7 million deaths are attributed to bacterial infections, of which 4.95 million are associated with drug-resistant pathogens, and 1·27 million are caused by bacterial pathogens resistant to the antibiotics available. Access to effective antibiotics when indicated prolongs life, reduces disability, reduces health-care expenses, and enables access to other life-saving medical innovations. Antimicrobial resistance undoes these benefits and is a major barrier to attainment of the Sustainable Development Goals, including targets for newborn survival, progress on healthy ageing, and alleviation of poverty. Adverse consequences from antimicrobial resistance are seen across the human life course in both health-care-associated and community-associated infections, as well as in animals and the food chain. The small set of effective antibiotics has narrowed, especially in resource-poor settings, and people who are very young, very old, and severely ill are particularly susceptible to resistant infections. This paper, the first in a Series on the challenge of antimicrobial resistance, considers the global scope of the problem and how it should be measured. Robust and actionable data are needed to drive changes and inform effective interventions to contain resistance. Surveillance must cover all geographical regions, minimise biases towards hospital-derived data, and include non-human niches.

A Simple Bacteremia Score for Predicting Bacteremia in Patients with Suspected Infection in the Emergency Department: A Cohort Study

Bacteremia is a life-threatening condition that has increased in prevalence over the past two decades. Prompt recognition of bacteremia is important; however, identification of bacteremia requires 1 to 2 days. This retrospective cohort study, conducted from 10 November 2014 to November 2019, among patients with suspected infection who visited the emergency department (ED), aimed to develop and validate a simple tool for predicting bacteremia. The study population was randomly divided into derivation and development cohorts. Predictors of bacteremia based on the literature and logistic regression were assessed. A weighted value was assigned to predictors to develop a prediction model for bacteremia using the derivation cohort; discrimination was then assessed using the area under the receiver operating characteristic curve (AUC). Among the 22,519 patients enrolled, 18,015 were assigned to the derivation group and 4504 to the validation group. Sixteen candidate variables were selected, and all sixteen were used as significant predictors of bacteremia (model 1). Among the sixteen variables, the top five with higher odds ratio, including procalcitonin, neutrophil-lymphocyte ratio (NLR), lactate level, platelet count, and body temperature, were used for the simple bacteremia score (model 2). The proportion of bacteremia increased according to the simple bacteremia score in both cohorts. The AUC for model 1 was 0.805 (95% confidence interval [CI] 0.785-0.824) and model 2 was 0.791 (95% CI 0.772-0.810). The simple bacteremia prediction score using only five variables demonstrated a comparable performance with the model including sixteen variables using all laboratory results and vital signs. This simple score is useful for predicting bacteremia-assisted clinical decisions.

Significant clinical differences but not outcomes between Klebsiella aerogenes and Enterobacter cloacae bloodstream infections: a comparative cohort study

PURPOSE

Although Klebsiella aerogenes (formerly Enterobacter aerogenes) and Enterobacter cloacae share many phenotypic characteristics, controversy exists as to whether they cause clinically distinguishable infections. The objective of this study was to determine the comparative incidence, determinants, and outcomes of K. aerogenes and E. cloacae bloodstream infections (BSI).

METHODS

Population-based surveillance was conducted among residents aged ≥ 15 years of Queensland, Australia during 2000-2019.

RESULTS

Overall 695 and 2879 incident K. aerogenes and E. cloacae BSIs were identified for incidence rates of 1.1 and 4.4 per 100,000 population, respectively. There was a marked increase in incidence associated with older age and with males with both species. Patients with K. aerogenes BSIs were older, were more likely male, to have community-associated disease, and to have a genitourinary source of infection. In contrast, E. cloacae were more likely to have co-morbid diagnoses of liver disease and malignancy and be associated with antimicrobial resistance. Enterobacter cloacae were significantly more likely to have repeat episodes of BSI as compared to K. aerogenes. However, no differences in length of stay or all cause 30-day case-fatality were observed.

CONCLUSION

Although significant demographic and clinical differences exist between K. aerogenes and E. cloacae BSI, they share similar outcomes.

The emergence of multidrug-resistant Gram-positive bloodstream infections in India - a single center prospective cohort study

Introduction

Gram-positive bloodstream infections (BSIs) are an emerging health concern, especially in resource-limited settings. There is a paucity of data regarding the antimicrobial resistance (AMR) pattern of Gram-positive BSIs. The rise in multidrug-resistant infections further convoluted antibiotic selection. We aimed to assess the incidence, clinical and microbiological profile, antimicrobial resistance (AMR) and outcome in Gram-positive BSIs.

Methods

This was a single-center prospective study conducted at a tertiary care hospital in Western India. All patients (age ≥18 years) with culture-proven Gram-positive BSIs were included. Data were collected on all patients' demography, risk factors, AMR and clinical outcome.

Results

A total of 210 clinically significant isolates were grown from July 2020 to December 2021. The incidence of Gram-positive BSIs was 29% (n=61); 55.9% of cases were healthcare-associated, while 44.1% were community-acquired. Coagulase-negative staphylococci (CoNS) were the major isolates (36.1%), followed by Enterococcus spp. (27.9%), methicillin-susceptible Staphylococcus aureus (MSSA) (18%) and methicillin-resistant Staphylococcus aureus (MRSA) (14.7%). The proportion of vancomycin and teicoplanin-resistant CoNS isolates was 13.6% and 19%. Among Enterococcus isolates, the proportion of vancomycin-resistant enterococci (VRE) and linezolid-resistant enterococci (LRE) were 11.8% and 5.9%. The overall mortality in Gram-positive BSIs was 42.6%. Older age, MRSA infection, septic shock, and high NLR were significantly associated with mortality. On the Cox regression model, age ≥65 years (HR: 2.5; 95%CI: 1.1-5.8; p=0.024) and MRSA infection (HR: 3.6; 95%CI: 1.5-8.5; p=0.021) were found as independent predictors of 30-day mortality.

Conclusions

This study found substantial mortality with Gram-positive BSIs, especially MRSA infections. Moreover, the emergence of VRE and LRE is also alarming. Active surveillance of AMR and evaluation of mortality predictors may help overcome the therapeutic challenges in managing BSIs.

Incidence, aetiology and temporal trend of bloodstream infections in southern Sweden from 2006 to 2019: a population-based study

BackgroundBloodstream infections (BSI) are a public health concern, and infections caused by resistant bacteria further increase the overall BSI burden on healthcare.AimTo provide a population-based estimate of BSI incidence and relate this to the forthcoming demographic ageing western population change.MethodsWe retrieved positive blood cultures taken from patients in the Skåne region, southern Sweden, 2006-2019 from the Clinical Microbiology Department database and estimated incidence rates (IR), stratified by age (0-49, 50-64, 65-79, ≥ 80 years), sex, year, and species and described antimicrobial susceptibility for Enterobacterales.ResultsWe identified 944,375 blood culture sets, and 129,274 (13.7%) were positive. After deduplication and removal of contaminants, 54,498 separate BSI episodes remained. In total, 30,003 BSI episodes (55%) occurred in men. The overall IR of BSI was 307/100,000 person-years, with an average annual increase of 3.0%. Persons ≥ 80 years had the highest IR, 1781/100,000 person-years, as well as the largest increase. Escherichia coli (27%) and Staphylococcus aureus (13%) were the most frequent findings. The proportion of Enterobacterales isolates resistant to fluoroquinolones and third generation cephalosporins increased from 8.4% to 13.6%, and 4.9% to 7.3%, (p for trend < 0.001), with the largest increase in the oldest age group.ConclusionWe report among the highest BSI IRs to date worldwide, with a higher proportion among elderly persons and males, including resistant isolates. Given expected demographic changes, these results indicate a possible substantial future BSI burden, for which preventive measures are needed.

Achromobacter Species: An Emerging Cause of Community-Onset Bloodstream Infections

Background: Case reports and small series indicate that Achromobacter species bloodstream infection (BSI) is most commonly a complication of hospitalization among patients with chronic lung disease. The aim of the present study was to determine the incidence, risk factors, and outcomes of Achromobacter sp. BSI in an Australian population. Methods: Retrospective, laboratory-based surveillance was conducted in Queensland, Australia (population ≈ 5 million) during 2000–2019. Clinical and outcome data were obtained by linkage to state hospital admissions and vital statistics databases. BSI diagnosed within the community or within the first two calendar days of stay in hospital were classified as community-onset. Community-onset BSIs were grouped into community-associated and healthcare-associated. Results: During more than 86 million person-years of surveillance, 210 incidents of Achromobacter sp. BSI occurred among 195 individuals for an overall age-and sex-standardized annual incidence of 2.6 per million residents. Older individuals and males were at highest risk (2.9 vs. 2.0 per million, IRR for males 1.5; 95% CI, 1.1–1.9; p = 0.008). Most (153; 73%) cases were of community-onset of which 100 (48%) and 53 (25%) were healthcare- and community-associated, respectively. An increasing proportion of community-onset cases were observed during twenty years of surveillance. Underlying medical illnesses were common with median (interquartile range) Charlson Comorbidity Index (CCI) scores of 3 (1–5). CCI scores of 0, 1, 2, and 3+ were observed in 37 (18%), 27 (13%), 40 (19%), and 105 (50%) of cases, respectively. All but one of the cases were admitted to hospital for a median (interquartile range) length of stay of 12 (5–34) days. All-cause case–fatality rates in hospital by day 30 and by day 90 were 30 (14%), 28 (13%), and 42 (20%), respectively. The 90-day case–fatality rate increased with increasing comorbidity and was 3% (1/37), 11% (3/27), 25% (10/40), and 27% (28/105) among those with Charlson Comorbidity Indices of 0, 1, 2, and 3+, respectively (p = 0.004). Conclusions: Although comorbidity is an important determinant of risk, most Achromobacter sp. BSI are of community-onset and one-fifth of cases occur in patients without significant underlying chronic co-morbidities. This study highlights the value of population-based methodologies to define the epidemiology of an infectious disease.

Thyroid function and risk of bloodstream infections: Results from the Norwegian prospective population-based HUNT Study

OBJECTIVE

Previous studies on thyroid function and risk of infection is conflicting and often stem from intensive care cohorts were nonthyroidal illness syndrome (NTIS) may be present. The objective of this study was to identify the risk of bloodstream infections (BSI) and BSI-related mortality with thyroid-stimulating hormone (TSH) levels within the reference range in a general population.

DESIGN

Prospective follow-up.

PARTICIPANTS

The HUNT2 (1995-97) included 34,619 participants with information on TSH levels.

MEASUREMENTS

Hazard ratios (HRs) with 95% confidence interval (CI) confirmed BSIs and BSI-related mortality until 2011.

RESULTS

During a median follow-up of 14.5 years, 1179 experienced at least one episode of BSI and 208 died within 30 days after a BSI. TSH levels within the reference range of 0.5-4.5 mU/L were not associated with the risk of first-time BSI, with an HR of 0.97 (95% CI: 0.90-1.04) per mU/L. Stratified by baseline age < or ≥65 years, TSH was inversely associated with the risk of BSI (HR: 0.88; 95% CI: 0.78-1.00 per mU/L) in the youngest age group only. Persons with any baseline thyroid disease had a 30% risk and the hyperthyroid subgroup a 57%, and hypothyroidism a 20% increased risk of BSI. TSH levels were not clearly associated with BSI mortality, but the HRs were imprecise due to few BSI-related deaths.

CONCLUSION

There was some evidence of a weak inverse association between TSH levels and the risk of BSI in persons below 65 years of age. The increased risk seen in persons with thyroid illness is probably explained by confounding by concurrent ill health.

Explaining sex differences in risk of bloodstream infections using mediation analysis in the population-based HUNT study in Norway

Previous studies indicate sex differences in incidence and severity of bloodstream infections (BSI). We examined the effect of sex on risk of BSI, BSI mortality, and BSI caused by the most common infecting bacteria. Using causal mediation analyses, we assessed if this effect is mediated by health behaviours (smoking, alcohol consumption), education, cardiovascular risk factors (systolic blood pressure, non-HDL cholesterol, body mass index) and selected comorbidities. This prospective study included 64,040 participants (46.8% men) in the population-based HUNT2 Survey (1995-1997) linked with hospital records in incident BSI. During median follow-up of 15.2 years, 1840 (2.9%) participants (51.3% men) experienced a BSI and 396 (0.6%) died (56.6% men). Men had 41% higher risk of first-time BSI (95% confidence interval (CI), 28-54%) than women. Together, health behaviours, education, cardiovascular risk factors and comorbidities mediated 34% of the excess risk of BSI observed in men. The HR of BSI mortality was 1.87 (95% CI 1.53-2.28), for BSI due to S. aureus 2.09 (1.28-2.54), S. pneumoniae 1.36 (1.05-1.76), E. coli 0.97 (0.84-1.13) in men vs women. This study shows that men have higher risk of BSI and BSI mortality than women. One-third of this effect was mediated by potential modifiable risk factors for incident BSI.

Sphingomonas paucimobilis bloodstream infection is a predominantly community-onset disease with significant lethality

BACKGROUND

Small case series and reports suggest that Sphingomonas paucimobilis is predominantly a cause of nosocomial bloodstream infections (BSI) with very low associated mortality. Our objective was to describe the epidemiology and outcome of Sphingomonas species BSI in a large Australian population.

METHODS

All residents of Queensland Australia with BSI due to Sphingomonas species identified within the publicly funded system during 2000-2019 were included.

RESULTS

A total of 282 incident episodes of Sphingomonas species BSI were identified for an age- and sex-adjusted incidence of 3.2 per million population annually. Incidence rates were highest in the tropical regions of the state. Most (94%) of the isolates were confirmed as Sphingomonas paucimobilis. Seventy-seven percent of the infections were of community-onset of which 48% were community-associated and 30% were healthcare-associated. The very young and old and males were at highest risk. Patients with community-associated disease were on average younger, had fewer co-morbidities, and were less likely to have polymicrobial infections. At least one comorbidity was identified in 62% with malignancy, diabetes, and lung disease most prevalent. The overall all cause 30-day case-fatality rate was 6%.

CONCLUSION

Sphingomonas paucimobilis BSI is a predominantly community-onset disease associated with a significant risk for death.

Increased Dietary Manganese Impairs Neutrophil Extracellular Trap Formation Rendering Neutrophils Ineffective at Combating Staphylococcus aureus

Dietary metals can modify the risk to infection. Previously, we demonstrated that heightened dietary manganese (Mn) during systemic Staphylococcus aureus infection increases S. aureus virulence. However, immune cells also operate in these same environments and the effect of dietary Mn on neutrophil function in vivo has not been assessed. This study reveals that increased concentrations of Mn impairs mitochondrial respiration and superoxide production in neutrophils responding to S. aureus. As a result, high Mn accelerates primary degranulation, while impairing suicidal neutrophil extracellular trap (NET) formation, which decreases bactericidal activity. In vivo, elevated dietary Mn accumulated extracellularly in the heart, indicating that excess Mn may be more bioavailable in the heart. Coinciding with this phenotype, neutrophil function in the heart was most impacted by a high Mn diet, as neutrophils produced lower levels of mitochondrial superoxide and underwent less suicidal NET formation. Consistent with an ineffective neutrophil response when mice are on a high Mn diet, S. aureus burdens were increased in the heart and mice were more susceptible to systemic infection. Therefore, elevated dietary Mn not only affects S. aureus but also renders neutrophils less capable of restricting staphylococcal infection.

Fingerprints of Element Concentrations in Infective Endocarditis Obtained by Mass Spectrometric Imaging and t-Distributed Stochastic Neighbor Embedding

Staphylococcus aureus-induced infective endocarditis (IE) is a life-threatening disease. Differences in virulence between distinct S. aureus strains, which are partly based on the molecular mechanisms during bacterial adhesion, are not fully understood. Yet, distinct molecular or elemental patterns, occurring during specific steps in the adhesion process, may help to identify novel targets for accelerated diagnosis or improved treatment. Here, we use laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) of post-mortem tissue slices of an established mouse model of IE to obtain fingerprints of element distributions in infected aortic valve tissue. Three S. aureus strains with different virulence due to deficiency in distinct adhesion molecules (fibronectin-binding protein A and staphylococcal protein A) were used to assess strain-specific patterns. Data analysis was performed by t-distributed stochastic neighbor embedding (t-SNE) of mass spectrometry imaging data, using manual reference tissue classification in histological specimens. This procedure allowed for obtaining distinct element patterns in infected tissue for all three bacterial strains and for comparing those to patterns observed in healthy mice or after sterile inflammation of the valve. In tissue from infected mice, increased concentrations of calcium, zinc, and magnesium were observed compared to noninfected mice. Between S. aureus strains, pronounced variations were observed for manganese. The presented approach is sensitive for detection of S. aureus infection. For strain-specific tissue characterization, however, further improvements such as establishing a database with elemental fingerprints may be required.

Pasteurella species bloodstream infections in Queensland, Australia, 2000-2019

Pasteurella species are infrequent but potentially severe causes of bloodstream infection (BSI). The objective of this study was to determine the incidence, risk factors, and outcomes of Pasteurella species BSI in a large Australian population. Retrospective, laboratory-based surveillance was conducted in Queensland, Australia (population ≈ 5 million) during 2000–2019, and clinical and outcome information was established by linkage to state hospital admissions and vital statistics databases. During more than 86 million person-years of surveillance, 272 incident Pasteurella species BSI occurred for an overall age- and sex-standardized annual incidence of 3.3 per million residents. The incidence of Pasteurella species BSI was highest in recent years and older individuals were at greatest risk. The median (interquartile range) Charlson Comorbidity Index was 2 (0–4) with scores of zero, 1, 2, and 3 + observed in 81 (30%), 37 (14%), 44 (16%), and 110 (40%) of cases. The 30-day all-cause case fatality was 9% (24/272) and patients who died had more comorbidities and were less likely to have community-associated disease. Although Pasteurella species are infrequent causes of BSI, older individuals and those with comorbidities are at highest risk. The burden of this disease may be expected to increase with an aging and more comorbid population.

Altered Mitochondrial Homeostasis during Systemic Lupus Erythematosus Impairs Neutrophil Extracellular Trap Formation Rendering Neutrophils Ineffective at Combating Staphylococcus aureus

Inflammation involves a delicate balance between pathogen clearance and limiting host tissue damage, and perturbations in this equilibrium promote disease. Patients suffering from autoimmune diseases, such as systemic lupus erythematosus (SLE), have higher levels of serum S100A9 protein and increased risk for infection. S100A9 is highly abundant within neutrophils and modulates antimicrobial activity in response to bacterial pathogens. We reasoned that increased serum S100A9 in SLE patients reflects accumulation of S100A9 protein in neutrophils and may indicate altered neutrophil function. In this study, we demonstrate elevated S100A9 protein within neutrophils from SLE patients, and MRL/lpr mice associates with lower mitochondrial superoxide, decreased suicidal neutrophil extracellular trap formation, and increased susceptibility to Staphylococcus aureus infection. Furthermore, increasing mitochondrial superoxide production restored the antibacterial activity of MRL/lpr neutrophils in response to S. aureus These results demonstrate that accumulation of intracellular S100A9 associates with impaired mitochondrial homeostasis, thereby rendering SLE neutrophils inherently less bactericidal.

Excess Burden of Critical Illness Related to Inflammatory Bowel Disease

BACKGROUND

Although inflammatory bowel disease (IBD) is associated with major morbidity and mortality, few studies have evaluated its associated burden of critical illness.

AIMS

We sought to examine the epidemiology and outcome of ICU admission among patients with IBD in north Brisbane, Australia.

METHODS

A population-based cohort design was utilized. All admissions to ICUs serving the Metro North Hospital and Health Service among adult residents during 2017-2019 were included. Data were obtained from ICU clinical information systems with linkages to statewide admissions and death registries.

RESULTS

Among 9,011 ICU admissions, 101 (1.1%) were among patients with IBD of which 57 (0.6%) and 44 (0.5%) had UC and CD, respectively. The incidence of ICU admission was 379, 1,336, 1,514, and 1,429 per 100,000 annually among those without IBD, CD, UC and IBD, respectively. Patients with IBD were at excess risk for admission across all age groups with women at highest risk under age 50 and men thereafter. The all cause 90-day case-fatality rates following ICU admission were not significantly different among patient groups and were 18%, 12%, 15%, and 12% for CD, UC, IBD, and non-IBD, respectively. However, as compared to non-IBD patients, those with CD (151.8 vs. 39.4 per 100,000; RR 3.85; 95% CI, 1.25-9.02; p=0.013); UC (159.4 vs 39.4 per 100,000; RR 4.05; 95% CI, 1.48-8.84; p=0.005), and IBD 155.6 vs 39.4 per 100,000; RR 3.95; 95% CI, 1.96-7.10; p=0.002) were at significantly higher risk for mortality.

CONCLUSIONS

Patients with IBD suffer a major burden of critical illness. This article is protected by copyright. All rights reserved.

Mitochondrial calcium uniporter affects neutrophil bactericidal activity during Staphylococcus aureus infection

Neutrophils simultaneously restrict Staphylococcus aureus dissemination and facilitate bactericidal activity during infection through the formation of neutrophil extracellular traps (NETs). Neutrophils that produce higher levels of mitochondrial superoxide undergo enhanced terminal NET formation (suicidal NETosis) in response to S. aureus; however, mechanisms regulating mitochondrial homeostasis upstream of neutrophil antibacterial processes are not fully resolved. Here, we demonstrate that mitochondrial calcium uptake 1 (MICU1)-deficient (MICU1^-/-) neutrophils accumulate higher levels of calcium and iron within the mitochondria in a mitochondrial calcium uniporter (MCU)-dependent manner. Corresponding with increased ion flux through the MCU, mitochondrial superoxide production is elevated, thereby increasing the propensity for MICU1^-/- neutrophils to undergo suicidal NETosis rather than primary degranulation in response to S. aureus. Increased NET formation augments macrophage killing of bacterial pathogens. Similarly, MICU1^-/- neutrophils alone are not more antibacterial towards S. aureus, but rather enhanced suicidal NETosis by MICU1^-/- neutrophils facilitates increased bactericidal activity in the presence of macrophages. Similarly, mice with a deficiency in MICU1 restricted to cells expressing LysM exhibit lower bacterial burdens in the heart with increased survival during systemic S. aureus infection. Coinciding with the decrease in S. aureus burdens, MICU1^-/- neutrophils in the heart produced higher levels of mitochondrial superoxide and undergo enhanced suicidal NETosis. These results demonstrate that ion flux by the MCU affects the antibacterial function of neutrophils during S. aureus infection.

Population-Based Study of Bloodstream Infection Incidence and Mortality Rates, Finland, 2004-2018

A 2-fold increase in incidence and death during this period emphasizes the need for additional prevention efforts.

We evaluated the incidence, outcomes, and causative agents of bloodstream infections (BSI) in Finland during 2004–2018 by using data from the national registries. We identified a total of 173,715 BSIs; annual incidence increased from 150 to 309 cases/100,000 population. BSI incidence rose most sharply among persons >80 years of age. The 1-month case-fatality rate decreased from 13.0% to 12.6%, but the 1-month all-cause mortality rate rose from 20 to 39 deaths/100,000 population. BSIs caused by Escherichia coli increased from 26% to 30% of all BSIs. BSIs caused by multidrug-resistant microbes rose from 0.4% to 2.8%, mostly caused by extended-spectrum β-lactamase-producing E. coli. We observed an increase in community-acquired BSIs, from 67% to 78%. The proportion of patients with severe underlying conditions rose from 14% to 23%. Additional public health and healthcare prevention efforts are needed to curb the increasing trend in community-acquired BSIs and antimicrobial drug–resistant E. coli.

Escherichia coli bloodstream infections in the western interior of British Columbia, Canada: a population-based cohort study

Our population-based study objectives were to describe characteristics and outcomes of Escherichia coli bloodstream infections (BSIs), and to evaluate factors associated with outcomes. We included incident E. coli BSIs from western interior residents (British Columbia, Canada; 04/2010–03/2020). We obtained data including patient demographics, location of onset, infection focus, Charlson comorbidity index (CCI), antimicrobial resistance, 30-day all-cause mortality and length of hospital stay (LOS). Using multivariable logistic regression models fitted with generalised estimating equations, we estimated factors associated with 30-day mortality and long post-infection LOS (>75th percentile). We identified 1080 incident E. coli BSIs in 1009 patients. The crude incidence and 30-day mortality rates were 59.1 BSIs and 6.8 deaths/100 000 person-years, respectively. The 30-day case fatality risk was 11.5%. Compared to community-acquired E. coli BSIs, either healthcare-associated or nosocomial cases had higher odds of 30-day mortality. Older cases, non-urogenital BSI foci and CCI ⩾ 3 had higher odds of 30-day mortality compared to younger cases, urogenital foci and CCI < 3. In patients that survived to discharge, those with extended-spectrum β-lactamase (ESBL)-producing E. coli BSIs, nosocomial BSIs, and CCI ⩾ 3 had higher odds of long post-infection LOS compared to those with non-ESBL-producing, community-acquired and healthcare-associated, and CCI < 3. There is a substantial disease burden from E. coli BSIs.

Spatially Targeted Proteomics of the Host-Pathogen Interface during Staphylococcal Abscess Formation

Staphylococcus aureus is a common cause of invasive and life-threatening infections that are often multidrug resistant. To develop novel treatment approaches, a detailed understanding of the complex host-pathogen interactions during infection is essential. This is particularly true for the molecular processes that govern the formation of tissue abscesses, as these heterogeneous structures are important contributors to staphylococcal pathogenicity. To fully characterize the developmental process leading to mature abscesses, temporal and spatial analytical approaches are required. Spatially targeted proteomic technologies such as micro-liquid extraction surface analysis offer insight into complex biological systems including detection of bacterial proteins and their abundance in the host environment. By analyzing the proteomic constituents of different abscess regions across the course of infection, we defined the immune response and bacterial contribution to abscess development through spatial and temporal proteomic assessment. The information gathered was mapped to biochemical pathways to characterize the metabolic processes and immune strategies employed by the host. These data provide insights into the physiological state of bacteria within abscesses and elucidate pathogenic processes at the host-pathogen interface.

Burden of bloodstream infection in older persons: a population-based study

BACKGROUND

Advancing age is a major risk factor for developing and dying from bloodstream infections (BSI). However, there is a paucity of population-based studies investigating the epidemiology of BSI in older persons.

OBJECTIVE

To define the incidence, clinical determinants, and risk factors for death among those aged 65 years and older with BSI.

METHODS

Population-based surveillance was conducted in the western interior of British Columbia, Canada, between April 1, 2010 and March 31, 2020. Chart reviews were conducted for clinical details and all cause case-fatality was established at 30-days follow-up.

RESULTS

A total of 1854 incident BSI were identified among 1657 individuals aged 65 and older for an annual incidence of 533.9 per 100,000 population; the incidence for those aged 65-74, 75-84, and ≥85 years was 375.3, 678.9, and 1046.6 per 100,000 population, respectively. Males were at significantly increased risk as compared to females (incidence rate ratio, IRR 1.44; 95% confidence interval, CI, 1.32-1.59; p<0.0001). The crude annual incidence increased by 50% during the study. However, this was related to shift in population demographics with no increase evident following age- and sex-standardization. Older patients were more likely to have healthcare-associated infections and genitourinary sources and less likely to have bone/joint or soft tissue infections. The proportion of patients with underlying congestive heart failure, stroke, and dementia increased, whereas diabetes and liver disease decreased with older age. The overall 30-day all cause case-fatality rate was 22.0% (364/1657). After adjustment for clinical focus, onset of infection, etiology, and co-morbidity in a logistic model, those aged 75-84 years (odds ratio, OR, 1.66; 95% CI, 1.25-2.21) and ≥ 85 years (OR, 1.98; 95% CI, 1.41-2.77) were at significantly increased risk for death as compared to those aged 65-74 years.

CONCLUSION

Bloodstream infection is common in older persons and is a major cause of death. Countries with aging populations worldwide should expect an increase burden associated with BSI in the coming years.

Occurrence and determinants of enterococcal bloodstream infections: a population-based study

Background: Although enterococci are common causes of bloodstream infections (BSIs), few studies have examined their epidemiology in non-selected populations.Objective: To examine the incidence and risk factors for development of enterococcal BSI.Methods: Surveillance for incident enterococcal BSI was conducted among all residents of the western interior of British Columbia, Canada during 2011-2018.Results: The overall annual incidence was 10.0 per 100,000 and was 6.6 and 2.7 per 100,000 for E. faecalis and E. faecium, respectively. Among the overall cohort of 145 incident cases of enterococcal BSI, 22 (15.2%) were community-associated, 63 (43.5%) were healthcare associated and 60 (41.4%) were hospital-onset. Enterococcal BSI was predominantly a disease of older adults with rare cases occurring among those aged less than 40 years. Males showed significantly increased risk compared to females (14.3 vs. 5.6 per 100,000; incidence rate ratio; IRR; 2.6; 95% confidence interval; CI; 1.8-3.8; p < .0001) and this was most pronounced with advanced age. Several co-morbid illnesses were associated with increased risk (IRR; 95% CI) for development of enterococcal BSI most importantly cancer (8.8; 6.0-12.9; p < .0001), congestive heart failure (5.7; 3.1-9.7; p < .0001), diabetes mellitus (4.4; 3.0-6.3; p < .0001) and stroke (3.7; 1.9-6.5; .0001). As compared to patients with E. faecalis, patients with E. faecium BSI were more likely to be of hospital-onset, more likely to have an intra-abdominal/pelvic focus, and trended towards higher 30-day case-fatality rate.Conclusions: Enterococci are relatively common causes of BSI. Although E faecalis and E faecium share commonalities they are epidemiologically distinguishable on several criteria.

High Burden of Extended-Spectrum β-Lactamase-Producing Escherichia coli and Klebsiella pneumoniae Bacteremia in Older Adults: A Seven-Year Study in Two Rural Thai Provinces

Bloodstream infection surveillance conducted from 2008 to 2014 in all 20 hospitals in Sa Kaeo and Nakhon Phanom provinces, Thailand, allowed us to look at disease burden, antibiotic susceptibilities, and recurrent infections caused by extended-spectrum β-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae. Of 97,832 blood specimens, 3,338 were positive for E. coli and 1,086 for K. pneumoniae. The proportion of E. coli isolates producing ESBL significantly increased from 19% to 22% in 2008-2010 to approximately 30% from 2011 to 2014 (P-value for trend = 0.02), whereas ESBL production among K. pneumoniae cases was 27.4% with no significant trend over time. Incidence of community-onset ESBL-producing E. coli increased from 5.4 per 100,000 population in 2008 to 12.8 in 2014, with the highest rates among persons aged ≥ 70 years at 79 cases per 100,000 persons in 2014. From 2008 to 2014, community-onset ESBL-producing K. pneumoniae incidence was 2.7 per 100,000, with a rate of 12.9 among those aged ≥ 70 years. Although most (93.6% of E. coli and 87.6% of K. pneumoniae) infections were community-onset, hospital-onset infections were twice as likely to be ESBL. Population-based surveillance, as described, is vital to accurately monitor emergence and trends in antimicrobial resistance, and in guiding the development of rational antimicrobial therapy recommendations.

Population-based risk factors for community-onset bloodstream infections

Although a number of comorbidities have been associated with development of bloodstream infection, actual risk factors have not been well defined and quantified in nonselected populations. We sought to quantify population-based risk factors for development of community-onset bloodstream infection (COBSI). Surveillance was conducted among all residents of the Western Interior of British Columbia, Canada, during 2011-2018. Risks were expressed as incidence rate ratios (IRR) with 95% confidence intervals (CI). The annual incidence was 147.1 per 100,000 and older individuals, and males were at overall higher risk. The median Charlson score was 2 (IQR, 0-3), and this was higher among those with healthcare-associated (2; IQR, 1-4) as compared to community-associated (1; IQR, 0-2; P < 0.0001) COBSI. Risk factors for development of COBSI included (IRR; 95% CI): HIV infection (8.89; 5.17-14.27), cancer (6.80; 6.13-7.54), congestive heart failure (4.68; 4.00-5.46), dementia (3.31; 2.82-3.87), diabetes mellitus (3.10; 2.80-3.42), cerebrovascular accident (2.79; 2.34-3.31), renal dysfunction (2.75; 2.33-3.22), chronic lung disease (2.03; 1.79-2.28), peripheral vascular disease (1.68; 1.39-2.01), and rheumatic disease (1.44; 1.14-1.79). Patients with multiple comorbid illnesses were older, more likely to be male, and have healthcare-associated BSI, higher rates of antimicrobial resistance, and different clinical foci of infection. A number of demographic and comorbid conditions significantly increase the risk for development of COBSI.

Occurrence and determinants of Klebsiella species bloodstream infection in the western interior of British Columbia, Canada

Background

Klebsiella species are among the most common causes of bloodstream infection (BSI). However, few studies have evaluated their epidemiology in non-selected populations. The objective was to define the incidence of, risk factors for, and outcomes from Klebsiella species BSI among residents of the western interior of British Columbia, Canada.

Methods

Population-based surveillance was conducted between April 1, 2010 and March 31, 2017.

Results

151 episodes were identified for an incidence of 12.1 per 100,000 population per year; the incidences of K. pneumoniae and K. oxytoca were 9.1 and 2.9 per 100,000 per year, respectively. Overall 24 (16%) were hospital-onset, 90 (60%) were healthcare-associated, and 37 (25%) were community-associated. The median patient age was 71.4 (interquartile range, 58.8–80.9) years and 88 (58%) cases were males. Episodes were uncommon among patients aged < 40 years old and no cases were observed among those aged < 10 years. A number of co-morbid medical illnesses were identified as significant risks and included (incidence rate ratio; 95% confidence interval) cerebrovascular accident (5.9; 3.3–9.9), renal disease 4.3; 2.5–7.0), cancer (3.8; 2.6–5.5), congestive heart failure (3.5; 1.6–6.6), dementia (2.9; 1.5–5.2), diabetes mellitus (2.6; 1.7–3.9), and chronic obstructive pulmonary disease (2.3; 1.5–3.5). Of the 141 (93%) patients admitted to hospital, the median hospital length stay was 8 days (interquartile range, 4–17). The in-hospital and 30-day all cause case-fatality rates were 24/141 (17%) and 27/151 (18%), respectively.

Conclusions

Klebsiella species BSI is associated with a significant burden of illness particularly among those with chronic co-morbid illnesses.

Bloodstream infection due to β-hemolytic streptococci: a population-based comparative analysis

PURPOSE

Although the burden of illness due to Streptococcus pyogenes is widely recognized, other β-hemolytic streptococci are also important causes of invasive infections. The objective of this study was to compare the population-based epidemiology of groups A, B, and C/G β-hemolytic streptococcal bloodstream infection (BSI).

METHODS

Population-based surveillance was conducted in the western interior of British Columbia, Canada, 2011-2018.

RESULTS

A total of 210 episodes were identified for an incidence of 14.4 per 100,000; the incidences of groups A, B and C/G streptococcal BSI were 4.2, 4.7, and 5.5 per 100,000, respectively. There was an increasing annual incidence of β-hemolytic streptococcal BSI from 2011 through to a peak incidence in 2016 that decreased thereafter. Fifty-two percent (110) of BSIs were community associated, 43% (91) were healthcare associated, and 4% (9) were hospital onset. Patients with group A were younger, more likely to be female, and have fewer co-morbidities than patients with groups B and C/G streptococcal BSI. The most common focus of infection was soft tissue (109/52%), followed by primary (33; 16%), and bone and joint (20; 10%) and these varied by streptococcal species (p < 0.001). The 30-day all-cause case fatality rate was 11% (24/210) and did not significantly vary by group (p = 0.7).

CONCLUSION

Although the determinants vary, the overall burden of disease related to BSI is similar amongst groups A, B and C/G β-hemolytic streptococci.

Inhospital death is a biased measure of fatal outcome from bloodstream infection

Purpose

Inhospital death is commonly used as an outcome measure. However, it may be a biased measure of overall fatal outcome. The objective of this study was to evaluate inhospital death as a measure of all-cause 30-day case fatality in patients with bloodstream infection (BSI).

Patients and methods

A population-based surveillance cohort study was conducted, and patients who died in hospital within 30 days (30-day inhospital death) were compared with those who died in any location by day 30 post BSI diagnosis (30-day all-cause case fatality).

Results

A total of 1,773 residents had first incident episodes of BSI. Overall, 299 patients died for a 30-day all-cause case fatality rate of 16.9%. Most (1,587; 89.5%) of the patients were admitted to hospital, and ten (5.4%) of the 186 patients not admitted to hospital died. Of the 1,587 admitted patients, 242 died for a 30-day inhospital death rate of 15.2%. A further 47 patients admitted to hospital died after discharge but within 30 days of BSI diagnosis for a 30-day case fatality rate among admitted patients of 18.2%. Patients who died following discharge within 30 days were older and more likely to have dementia.

Conclusion

The use of inhospital death is a biased measure of true case fatality.

Bacterial Distribution and Risk Factors of Nosocomial Blood Stream Infection in Neurologic Patients in the Intensive Care Unit

OBJECTIVE

To investigate the risk factors and analyze the distribution of pathogens to provide a basis for the prevention of nosocomial blood stream infections (BSI) and reduce the incidence and mortality of nosocomial BSI in neurologic patients.

PATIENTS AND METHODS

A retrospective chart review of neurologic patients admitted to an adult intensive care unit from January 2012 to December 2017 was conducted. Every positive blood culture, clinical demographic, microbiologic and laboratory result, as well as 28-day outcome data, were compiled on a data collection sheet. The clinical significance of each isolate was determined; in addition, the antimicrobial susceptibilities of causative pathogens and the most likely source were recorded.

RESULTS

During the five-year study period, there were 121 nosocomial BSI yielding 151 isolates in 404 neurologic patients. Eighty-one percent of nosocomial BSI were monomicrobial. Gram-positive organisms caused 67.9% of these BSI, gram-negative organisms caused 32.1%, and fungi caused 0.8%. The crude incidence rate was approximately 29.9%, and the mortality of nosocomial BSI was as high as 29.8%. Intravascular lines were the most common source of nosocomial BSI (79.3%). The most common organisms causing BSI were coagulase-negative staphylococci (CoNS; 44.6% of isolates), Staphylococcus aureus (17.4%), Klebsiella species (11.5%), and Acinetobacter spp. (11.5%). Multivariable regression analysis revealed that the use of antibiotic agents in the 90 days prior (odds ratio [OR], 5.81; 95% confidence interval [CI], 3.18-10.62; p = 0.001), brain trauma (OR, 0.28; 95% CI, 0.15-0.51; p = 0.001), and transfusion (OR, 3.02; 95% CI, 1.45-6.29; p = 0.001) were significant predictors of nosocomial BSI.

CONCLUSIONS

The incidence and mortality of nosocomial BSI were high in our neurologic patients. Strictly aseptic operations, hand hygiene, and reasonable use of transfusions and antibiotic agents are effective measures to prevent nosocomial BSI.

Machine learning for fast identification of bacteraemia in SIRS patients treated on standard care wards: a cohort study

Bacteraemia is a life-threating condition requiring immediate diagnostic and therapeutic actions. Blood culture (BC) analyses often result in a low true positive result rate, indicating its improper usage. A predictive model might assist clinicians in deciding for whom to conduct or to avoid BC analysis in patients having a relevant bacteraemia risk. Predictive models were established by using linear and non-linear machine learning methods. To obtain proper data, a unique data set was collected prior to model estimation in a prospective cohort study, screening 3,370 standard care patients with suspected bacteraemia. Data from 466 patients fulfilling two or more systemic inflammatory response syndrome criteria (bacteraemia rate: 28.8%) were finally used. A 29 parameter panel of clinical data, cytokine expression levels and standard laboratory markers was used for model training. Model tuning was performed in a ten-fold cross validation and tuned models were validated in a test set (80:20 random split). The random forest strategy presented the best result in the test set validation (ROC-AUC: 0.729, 95%CI: 0.679–0.779). However, procalcitonin (PCT), as the best individual variable, yielded a similar ROC-AUC (0.729, 95%CI: 0.679–0.779). Thus, machine learning methods failed to improve the moderate diagnostic accuracy of PCT.

Antimicrobial Nonsusceptibility of Gram-Negative Bloodstream Isolates, Veterans Health Administration System, United States, 2003-20131

Bacteremia caused by gram-negative bacteria is associated with serious illness and death, and emergence of antimicrobial drug resistance in these bacteria is a major concern. Using national microbiology and patient data for 2003–2013 from the US Veterans Health Administration, we characterized nonsusceptibility trends of community-acquired, community-onset; healthcare-associated, community-onset; and hospital-onset bacteremia for selected gram-negative bacteria (Escherichia coli, Klebsiella spp., Pseudomonas aeruginosa, and Acinetobacter spp.). For 47,746 episodes of bacteremia, the incidence rate was 6.37 episodes/10,000 person-years for community-onset bacteremia and 4.53 episodes/10,000 patient-days for hospital-onset bacteremia. For Klebsiella spp., P. aeruginosa, and Acinetobacter spp., we observed a decreasing proportion of nonsusceptibility across nearly all antimicrobial drug classes for patients with healthcare exposure; trends for community-acquired, community-onset isolates were stable or increasing. The role of infection control and antimicrobial stewardship efforts in inpatient settings in the decrease in drug resistance rates for hospital-onset isolates needs to be determined.

Are we missing the Staphylococcus aureus bacteraemia forest for the MRSA trees?

In this edition of the journal, Jokinen et al. report on a population based study of Staphylococcus aureus bacteraemia (SAB) in Finland. They observe increasing incidence of cases over time that are associated with an increase in blood culture sampling. As compared to methicillin-sensitive SAB that increases during the study period, the incidence of methicillin-resistant SAB increases and then decreases. The proportion of cases with penicillin-sensitive SAB markedly increases in the study representing 43% of isolates in the most recent year of surveillance. While much attention and focus is typically placed on methicillin-resistant SAB, the major part of the burden of illness associated with SAB is from methicillin-sensitive and penicillin-sensitive strains. A narrow focus on prevention of methicillin-resistant Staphylococcus aureus will only have a limited impact on the overall burden of disease due to SAB.

Staphylococcus aureus bacteraemia and endocarditis - epidemiology and outcome: a review

PURPOSE

To review the epidemiology of Staphylococcus aureus bacteraemia (SAB) and endocarditis (SAE), and discuss the short- and long-term outcome.  Materials and methods: A literature review of the epidemiology of SAB and SAE.

RESULTS

The reported incidence of SAB in Western countries is 16-41/100,000 person-years. Increasing incidence has been observed in many regions, in Iceland by 27% during 1995-2008. The increase is believed to depend on changes in population risk factors and possibly better and more frequent utilization of diagnostic procedures. S. aureus is now the leading causes of infective endocarditis (IE) in many regions of the world. It accounts for 15-40% of all IE cases, and the majority of cases in people who inject drugs (PWID). Recently, the incidence of SAE in PWID in Stockholm, Sweden, was found to be 2.5/1000 person-years, with an in-hospital mortality of 2.5% in PWID as compared to 15% in non-drug users. The 30-day mortality associated with SAB amounts to 15-25% among adults in Western countries, but is lower in children (0-9%). Mortality associated with SAE is high (generally 20-30% in-hospital mortality), and symptomatic cerebral embolizations are common (12-35%). The 1-year mortality reported after SAB and SAE is 19-62% and reflects deaths from underlying diseases and complications caused by the infection. In a subset of SAE cases, valvular heart surgery is needed (15-45%), but active intravenous drug use seems to be a reason to refrain from surgery. Despite its importance, there are insufficient data on the optimal management of SAB and SAE, especially on the required duration of antibiotic therapy.  Conclusions: The epidemiology of SAB and SAE has been changing in the past decades. They still carry a substantial morbidity and mortality. Intensified studies on treatment are warranted for improving patient outcome.

Burden of bloodstream infection in an area of Mid-Norway 2002-2013: a prospective population-based observational study

BACKGROUND

Studies from several countries indicate that the incidence and mortality of bloodstream infection (BSI) have been increasing over time.

METHODS

We studied the burden of disease and death related to BSI in a defined geographical area of Mid-Norway, where BSI episodes were prospectively recorded by the same microbiological department during 12 consecutive years. Death from BSI was defined as death within 30 days of BSI detection. Age and sex standardized incidence and mortality rates and case fatality rates were calculated.

RESULTS

Between 2002 and 2013, 1995 episodes of BSI in 1719 patients aged 16 to 99 years were included. The overall incidence of BSI was 215 per 100,000 person-years. The incidence increased exponentially with age, particularly in males. The incidence increased from 205 to 223 per 100,000 person-years from 2002-07 to 2008-13. Escherichia coli was the most frequently isolated infective agent, followed by Streptococcus pneumoniae and Staphylococcus aureus. The rate of S. pneumoniae BSI decreased over time in males (on average by 9.2% annually), but not in females. The total rate of BSI microbes with acquired resistance increased slightly over time, but did not exceed 2 episodes per 100,000 person-years. The mortality of BSI was 32 per 100,000 person-years, higher in males than in females (36 vs. 28 per 100,000 person-years) and was significantly higher in old age, particularly in males. The total BSI mortality was similar in the first and second halves of the study period, but the mortality of S. pneumoniae BSI decreased in males (15.0% annually). The crude case fatality decreased from the first to the second half of the study period (17.2% to 13.1%; p = 0.014). The rate of blood culture sampling increased more than twofold during the study period.

CONCLUSIONS

The mortality of BSI remained stable during 2002-2013. At the same time, BSI incidence increased and case fatality rate decreased, perhaps because an increased rate of blood culture sampling may have led to improved detection of milder BSI episodes. Very low, yet slightly increasing rates of microbes with acquired resistance were observed.

Burden of community-onset bloodstream infections, Western Interior, British Columbia, Canada

Although community-onset bloodstream infection (BSI) is recognized as a major cause of morbidity and mortality, its epidemiology has not been well defined in non-selected populations. We conducted population-based surveillance in the Interior Health West region of British Columbia, Canada in order to determine the burden associated with community-onset BSI. A total of 1088 episodes were identified for an overall annual incidence of 117·8/100 000 of which 639 (58·7%) were healthcare-associated (HA) and 449 (41·3%) were community-associated (CA) BSIs for incidences of 69·2 and 48·6/100 000, respectively. The incidence of community-onset BSI varied by age and gender and elderly males were at the highest risk. Overall 964 (88·6%) episodes resulted in hospital admission for a median length of stay of 8 days; the total days of acute hospitalization associated with community-onset BSI was 13 530 days or 1465 days/100 000 population per year. The in-hospital mortality rate was 10·6% (102/964) and this was higher for HA-BSI (72/569, 12·7%) compared to CA-BSI (30/395, 7·6%, P = 0·014) episodes. Community-onset BSI, especially HA-BSI, is associated with a major burden of illness.

Bloodstream infections, antibiotic resistance and the practice of blood culture sampling in Germany: study design of a Thuringia-wide prospective population-based study (AlertsNet)

INTRODUCTION

Bloodstream infections are a major cause of death worldwide; blood culture (BC) sampling remains the most important tool for their diagnosis. Current data suggest that BC rates in German hospitals are considerably lower than recommended; this points to shortfalls in the application of microbiological analyses. Since early and appropriate BC diagnostics are associated with reduced case fatality rates and a shorter duration of antimicrobial therapy, a multicomponent study for the improvement of BC diagnostics was developed.

METHODS AND ANALYSIS

An electronic BC registry established for the German Federal state of Thuringia is the structural basis of this study. The registry includes individual patient data (microbiological results and clinical data) and institutional information for all clinically relevant positive BCs at the participating centres. First, classic result quality indicators for bloodstream infections (eg, sepsis rates) will be studied using Poisson regression models (adjusted for institutional characteristics) in order to derive relative ranks for feedback to clinical institutions. Second, a target value will be established for the process indicator BC rate. On the basis of this target value, recommendations will be made for a given combination of institutional characteristics as a reference for future use in quality control. An interventional study aiming at the improvement of BC rates will be conducted thereafter. On the basis of the results of a survey in the participating institutions, a targeted educational intervention will be developed. The success of the educational intervention will be measured by changes in the process indicator and the result indicators over time using a pre-post design.

ETHICS AND DISSEMINATION

Ethics approval was obtained from the Ethics committee of the University Hospital Jena and from the Ethics committee of the State Chamber of Physicians of Thuringia. Findings of AlertsNet will be disseminated through public media releases and publications in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

DRKS00004825.

Population-based epidemiology and microbiology of community-onset bloodstream infections

Bloodstream infection (BSI) is a major cause of infectious disease morbidity and mortality worldwide. While a positive blood culture is mandatory for establishment of the presence of a BSI, there are a number of determinants that must be considered for establishment of this entity. Community-onset BSIs are those that occur in outpatients or are first identified <48 h after admission to hospital, and they may be subclassified further as health care associated, when they occur in patients with significant prior health care exposure, or community associated, in other cases. The most common causes of community-onset BSI include Escherichia coli, Staphylococcus aureus, and Streptococcus pneumoniae. Antimicrobial-resistant organisms, including methicillin-resistant Staphylococcus aureus and extended-spectrum β-lactamase/metallo-β-lactamase/carbapenemase-producing Enterobacteriaceae, have emerged as important etiologies of community-onset BSI.

Validity of calendar day-based definitions for community-onset bloodstream infections

BACKGROUND

Community-onset (CO) bloodstream infections (BSI) are those BSI where the blood culture is drawn <48 hours from hospital admission. However, exact times of culture draw or hospital admission are not always available. We evaluated the validity of using 2- or 3- calendar day based definitions for CO-BSI by comparing to a "gold standard" 48-hour definition.

FINDINGS

Among the population-based cohort of 14,106 episodes of BSI studied, 10,543 were classified as CO based on "gold standard" 48-hour criteria. When 2-day and 3-day definitions were applied, 10,396 and 10,707 CO-BSI episodes were ascertained, respectively. All but 147 (1.4%) true CO-BSI cases were included by using the 2-day definition. When the 3-day definition was applied, all cases of CO-BSI were identified but and additional 164 (1.5%) cases of hospital-onset HO-BSI were also included. Thus the sensitivity and specificity of the 2-day definition was 98.6% and 100% and for the 3-day definition was 100% and 98.5%, respectively. Overall, only 311 (2.2%) cases were potentially miss-classifiable using either the 2- or 3-calendar day based definitions.

CONCLUSIONS

Use of either a 2- or 3-day definition is highly accurate for classifying CO-BSI.

Low mortality of Staphylococcus aureus bacteremia in Icelandic children: nationwide study on incidence and outcome

BACKGROUND

Staphylococcus aureus is a major cause of blood stream infections, but population-based studies on pediatric S. aureus bacteremia (SAB) are sparse. The objective of the study was to evaluate the incidence and mortality of SAB in Icelandic children over time, and to assess the proportions of nosocomial and health-care-associated infections.

METHODS

Children <18 years with positive blood cultures for S. aureus from January 1995 through December 2011 were identified retrospectively at the clinical microbiology laboratories performing blood cultures in Iceland. Clinical data were collected from medical records.

RESULTS

In total, 140 children had 146 distinct episodes of SAB. Bacteremia-related mortality was 0.7% (1/146), all-cause 30-day mortality, 1.4% (2/146), and 1-year mortality, 3.6% (5/140). The annual incidence of SAB was 10.9/100,000 children, decreasing by 36% from 13.1/100,000 in 1995-2003 to 8.4/100,000 in 2004-2011 (P < 0.001). At the same time the annual number of blood cultures analyzed at the main study site decreased from 1529 to 1143 (25%). SAB incidence was highest in infants (<1 year), 58.8/100,000. Of 146 episodes 50 (34%) were nosocomial, 21 (14%) health-care associated and 75 (51%) community acquired. No methicillin-resistant S. aureus isolate was identified.

CONCLUSIONS

In this nationwide study on pediatric SAB, the case fatality ratio was very low. A decreasing incidence was seen, possibly related to fewer blood cultures being collected. Nosocomial and health-care-associated infections accounted for 50% of the cases. The findings provide useful information on the epidemiology and outcome of SAB in children.

A risk prediction model for screening bacteremic patients: a cross sectional study

Background

Bacteraemia is a frequent and severe condition with a high mortality rate. Despite profound knowledge about the pre-test probability of bacteraemia, blood culture analysis often results in low rates of pathogen detection and therefore increasing diagnostic costs. To improve the cost-effectiveness of blood culture sampling, we computed a risk prediction model based on highly standardizable variables, with the ultimate goal to identify via an automated decision support tool patients with very low risk for bacteraemia.

Methods

In this retrospective hospital-wide cohort study evaluating 15,985 patients with suspected bacteraemia, 51 variables were assessed for their diagnostic potency. A derivation cohort (n = 14.699) was used for feature and model selection as well as for cut-off specification. Models were established using the A2DE classifier, a supervised Bayesian classifier. Two internally validated models were further evaluated by a validation cohort (n = 1,286).

Results

The proportion of neutrophile leukocytes in differential blood count was the best individual variable to predict bacteraemia (ROC-AUC: 0.694). Applying the A2DE classifier, two models, model 1 (20 variables) and model 2 (10 variables) were established with an area under the receiver operating characteristic curve (ROC-AUC) of 0.767 and 0.759, respectively. In the validation cohort, ROC-AUCs of 0.800 and 0.786 were achieved. Using predefined cut-off points, 16% and 12% of patients were allocated to the low risk group with a negative predictive value of more than 98.8%.

Conclusion

Applying the proposed models, more than ten percent of patients with suspected blood stream infection were identified having minimal risk for bacteraemia. Based on these data the application of this model as an automated decision support tool for physicians is conceivable leading to a potential increase in the cost-effectiveness of blood culture sampling. External prospective validation of the model's generalizability is needed for further appreciation of the usefulness of this tool.

Characteristics of hospital-acquired and community-onset blood stream infections, South-East Austria

Purpose

The objective of this study was to compare epidemiology, causative pathogens, outcome, and levels of laboratory markers of inflammation of community-onset (i.e. community-acquired and healthcare-associated) and hospital-acquired bloodstream infection (BSI) in South-East Austria.

Methods

In this prospective cohort study, 672 patients fulfilling criteria of systemic inflammatory response syndrome with positive peripheral blood cultures (277 community-onset [192 community-acquired, 85 healthcare-associated BSI], 395 hospital-acquired) were enrolled at the Medical University of Graz, Austria from 2011 throughout 2012. Clinical, microbiological, demographic as well as outcome and laboratory data was collected.

Results

Escherichia coli followed by Staphylococcus aureus were the most frequently isolated pathogens. While Streptococcus spp. and Escherichia coli were isolated more frequently in patients with community-onset BSI, Enterococcus spp., Candida spp., Pseudomonas spp., Enterobacter spp., and coagulase-negative staphylococci were isolated more frequently among those with hospital-acquired BSI. With regard to the outcome, 30-day (82/395 vs. 31/277; p = 0.001) and 90-day mortality (106/395 vs. 35/277; p<0.001) was significantly higher among patients with hospital-acquired BSI even though these patients were significantly younger. Also, hospital-acquired BSI remained a significant predictor of mortality in multivariable analysis. At the time the blood cultures were drawn, patients with community-onset BSI had significantly higher leukocyte counts, neutrophil-leucocyte ratios as well as C-reactive protein, procalcitonin, interleukin-6 and serum creatinine levels when compared to those with hospital-acquired BSI. Patients with healthcare-associated BSI presented with significantly higher PCT and creatinine levels than those with community-acquired BSI.

Conclusions

Hospital-acquired BSI was associated with significantly higher 30- and 90-day mortality rates. Hospital-acquired BSI therefore poses an important target for the most aggressive strategies for prevention and infection control.