Source of infection and other factors associated with case fatality in community-acquired bacteremia—a Danish population-based cohort study from 1992 to 1997

Antimicrobial resistance trends of Escherichia coli bloodstream isolates: a population-based study, 1998-2007

BACKGROUND

There have been contradictory results regarding temporal changes in the antimicrobial resistance of Escherichia coli from tertiary care centres. Therefore, we performed a population-based investigation to examine in vitro antimicrobial resistance trends of E. coli bloodstream isolates.

METHODS

In this retrospective population-based incidence study, we identified 461 unique patients with first episodes of E. coli bloodstream infection (BSI) from 1 January 1998 to 31 December 2007 through microbiology records at the two laboratories in Olmsted County, Minnesota. Logistic regression was used to examine temporal changes in antimicrobial resistance and Poisson regression for changes in incidence rates.

RESULTS

The median age of patients with E. coli BSI was 69 years; 306 (66.4%) were female. The age-adjusted incidence rate of E. coli BSI per 100 000 person-years was 48.0 (95% CI: 42.5-53.4) in females and 34.0 (95% CI: 28.6-39.6) in males. The urinary tract was the most common primary source of infection (79.8%). During the study period, resistance rates of E. coli bloodstream isolates increased from 32% to 53% for ampicillin, from 23% to 45% for ampicillin/sulbactam, from 9% to 28% for trimethoprim/sulfamethoxazole and from 0% to 12% for ciprofloxacin. Resistance rates to carbapenems, cephalosporins and piperacillin/tazobactam remained low and stable.

CONCLUSIONS

To our knowledge, this is the first population-based study on antimicrobial resistance trends of E. coli bloodstream isolates in the USA. We demonstrated linear trends of increasing resistance among these isolates to three different classes of antimicrobial over the past decade.

Escherichia coli phylogenetic groups are associated with site of infection and level of antibiotic resistance in community-acquired bacteraemia: a 10 year population-based study in Denmark

OBJECTIVES

The aim of this study was to assess whether Escherichia coli phylogenetic groups were associated with the site of infection and the level of antibiotic resistance in community-acquired bacteraemia (CAB).

METHODS

The population-based cohort study included 1533 unique isolates of E. coli from Danish patients with CAB during a 10 year period. Triplex PCR was used to classify the phylogenetic groups, and susceptibility testing was performed by disc diffusion. Data were analysed using contingency tables and logistic regression.

RESULTS

Overall, 65.9% of the 1533 E. coli isolates belonged to phylogroup B2, 16.6% to D, 13.1% to A and 4.4% to B1. B2 was the most prevalent group for all sites of infection, ranging from 69.9% in cases with a urinary tract site of infection to 54.8% in cases with a hepatobiliary tract site of infection. Antibiotic resistance to one and more than three antibiotics, respectively, was most frequent in group D (11.4%/33.9%), followed by A (5.5%/26.9%), B1 (5.9%/19.1%) and B2 (6.7%/7.5%). Regression analysis, with group B2 as reference, confirmed that groups A and B1 were associated with a site of infection other than the urinary tract and that groups A and D were associated with resistance to antibiotics including ampicillin, sulphonamide, trimethoprim, gentamicin and quinolones.

CONCLUSIONS

Phylogenetic group B2 was predominant in E. coli CAB. This was the least resistant of the four groups. Phylogroups A and B1 were associated with sites of infection other than the urinary tract, and resistance to multiple antibiotics was most prevalent for groups A and D.

Potential clinical benefit of the in situ hybridization method for the diagnosis of sepsis

Despite the significant development of antibiotics, sepsis is still associated with high morbidity and mortality rates. The identification of pathologic organisms at an early stage of sepsis is critical to improve the outcome, but this is difficult to achieve with the conventional method of blood culture (BC). It has been demonstrated that the genes of pathogenic organisms surviving in neutrophils were detectable with in situ hybridization (ISH) and this method was useful for the accurate and rapid diagnosis of sepsis. In this study, we applied ISH to blood smears 60 patients with suspected sepsis. BC was also carried out using the same blood samples to investigate the diagnostic value of ISH. The number of positive results obtained by ISH was approximately four times higher than that obtained by BC (ISH, 25 [41.7%]; BC, 7 [11.7%]). The positive rate in the 21 patients given antibiotics was 61.9% by ISH (13 patients) and 4.7% by BC (1 patient). The antibiotic treatments targeting the organisms detected by either procedure showed a beneficial clinical outcome. Positive results by ISH were obtained earlier than those with BC (ISH, within 1 day; BC, several days). We conclude that ISH is a useful method for the rapid diagnosis of sepsis.

The changing burden of pediatric bloodstream infections in Calgary, Canada, 2000-2006

BACKGROUND

The epidemiology of pediatric bloodstream infection has not been well defined in general populations. The primary objective of this study was to describe the burden of illness of pediatric bloodstream infections in a large Canadian region and secondarily to assess the effect of implementation of universal infant immunization with 7-valent pneumococcal conjugate vaccine (PCV7) in 2002.

METHODS

Surveillance for all bloodstream infections was conducted among pediatric (<18 years) residents of the Calgary Health Region during 2000-2006.

RESULTS

Nine hundred ninety-five episodes of bloodstream infection occurred for an overall annual incidence of 53.7 per 100,000. Forty-eight percent were community-acquired, 27% were nosocomial-acquired, and 26% were healthcare-associated community onset. The risk for bloodstream infection was highest in neonates. The annual incidence of bloodstream infection changed significantly (P < 0.001) and was attributed to a decreasing incidence of community (P = 0.001) acquired disease. The most common species isolated were Streptococcus pneumoniae, Staphylococcus aureus, and Escherichia coli. Overall rates of pneumococcal infection decreased significantly in the post-PCV7 era (2004-2006) as compared with pre-PCV7 era (2000-2001) (4.6 vs. 13.6 per 100,000; P < 0.0001). This was even more pronounced in the subset with community-acquired disease (3.0 vs. 11.3 per 100,000; P < 0.0001) especially in the age group between 1 and 23 months of age (7.3 vs. 58.9 per 100,000; P < 0.0001). The overall mortality rate was 2 per 100,000/yr.

CONCLUSIONS

Bloodstream infections are an important cause of disease in children. Implementation of PCV7 has been associated with a significant reduction in the overall burden of disease.

Short-term mortality in relation to age and comorbidity in older adults with community-acquired bacteremia: a population-based cohort study

OBJECTIVES

To assess 30-day mortality from bacteremia in relation to age and comorbidity and the association between age and mortality with increasing comorbidity.

DESIGN

Population-based cohort study.

SETTING

North Jutland County, Denmark.

PARTICIPANTS

Adults in medical wards with community-acquired bacteremia, 1995 to 2004.

MEASUREMENTS

Smoothed mortality curves and computed mortality rate ratios (MRRs) using Cox regression analysis.

RESULTS

Two thousand eight hundred fifty-one patients, 851 aged 15 to 64, 1,092 aged 65 to 79, and 909 aged 80 and older were included. Mortality increased linearly with age. Compared with patients younger than 65, adjusted MRRs in patients aged 65 to 79 and 80 and older were 1.5 (95% confidence interval (CI)=1.2-2.0) and 1.8 (95% CI=1.4-2.3), respectively. Mortality also increased with level of comorbidity. Compared with patients with low comorbidity, adjusted MRRs in patients with medium and high comorbidity were 1.5 (95% CI=1.2-1.8) and 1.7 (95% CI=1.4-2.2), respectively. Regardless of the level of comorbidity, MRRs were consistently higher in older than in younger patients.

CONCLUSION

Older age and greater comorbidity predicted mortality, and increasing age-related comorbidity did not explain the effect of age.

Escherichia coli bacteraemia in Canberra: incidence and clinical features

OBJECTIVE

To determine the population incidence and clinical features of Escherichia coli bacteraemia in Canberra, Australia.

DESIGN, SETTING AND PARTICIPANTS

Canberra (including the nearby local government areas of Queanbeyan and Yarrowlumla) has a geographically isolated population of about 366 000 people. Its six hospitals also provide tertiary medical services for the surrounding region. Confining our analysis (by residential postcodes) to Canberra residents only, we used microbiology laboratory records and population statistics to calculate the population incidence of E. coli bacteraemia from January 2000 to December 2004. Clinical data were also collected prospectively on episodes occurring within three of the hospitals.

MAIN OUTCOME MEASURES

Population incidence of E. coli bacteraemia; place of acquisition of infection; focus of infection within body; recovery, new morbidity or death at 7 days.

RESULTS

During the 5-year period, 515 episodes of E. coli bacteraemia occurred in Canberra residents, an incidence of 28 per 100 000 population per year. The highest rate was in men aged > or = 80 years (463 per 100 000). Overall, E. coli bacteraemia occurred in equal numbers in males and females, but incidence was higher in males aged < 1 year and > or = 60 years. Most episodes occurred in people aged > or = 60 years (316/511 [62%]) and most were community-associated (347/511 [68%]). Half the infections (257/511) had a genitourinary focus and 28% (141/511) a gastrointestinal focus. The 7-day case-fatality rate was 5%. Prostate biopsies and urinary catheters were notable preventable foci of health care-associated bacteraemia. Resistance of isolates to gentamicin (2.1%), ciprofloxacin (1.8%) and cefotaxime (0.4%) was low.

CONCLUSIONS

E. coli is the most common cause of bacteraemia in Canberra, and incidence increases with age. Most cases have a community onset, but many episodes are related to health care procedures. Ongoing surveillance is important for identifying risk factors that may be modified to reduce disease.

Peptide nucleic acid fluorescence in situ hybridization for rapid detection of Klebsiella pneumoniae from positive blood cultures

This study evaluated a novel peptide nucleic acid (PNA) probe targeting a region of the 23S rRNA gene of Klebsiella pneumoniae by fluorescence in situ hybridization (FISH). Analytical performance was determined using 39 reference strains and other well-characterized strains of Klebsiella spp. and Enterobacter aerogenes. The probe was found to be specific for the K. pneumoniae complex (K. pneumoniae including Klebsiella ozaenae and Klebsiella variicola). The diagnostic accuracy was evaluated with 264 blood cultures containing Gram-negative rods. Using conventional identification as the reference, performance specifications were as follows: sensitivity 98.8 %, specificity 99.5 %, positive predictive value 98.8 % and negative predictive value 99.5 %. Discrepancies were resolved by PNA FISH retest and phenotypic tests. In conclusion, the K. pneumoniae probe provided an accurate diagnosis within 3 h and may supplement other methods for direct identification of Gram-negative bacteria.

Prevention of primary bacteraemia

This overview provides information on recent advances in the prevention of primary bacteraemia, commonly defined as bloodstream infection without a documented source of infection, but including those resulting from an intravenous or arterial line infection. The potential to prevent community-acquired, primary bacteraemia is still limited and may be targeted mainly at vaccines for high-risk groups. In contrast, the prevention of catheter-related bacteraemia has seen substantial progress within the last 10 years. Consequently, intravascular device-related bacteraemia has become largely preventable under routine working conditions. Independent of the use of antibiotic-coated catheters, the implementation of clinical pathways and multimodal preventive strategies directed at several risk factors of catheter-related bacteraemia is a successful strategy to reduce this potentially life-threatening infection and deserves future health services research.

[Guidelines for the diagnosis and treatment of patients with bacteriemia. Guidelines of the Sociedad Española de Enfermedades Infecciosas y Microbiología Clínica]

Bacteremia is a complex clinical syndrome in constant transformation that is an important, growing cause of morbidity and mortality. Even though there is a great deal of specific information about bacteremia, few comprehensive reviews integrate this information with a practical AIM. The main objective of these Guidelines, which target hospital physicians, is to improve the clinical care provided to patients with bacteremia by integrating blood culture results with clinical data, and optimizing the use of diagnostic procedures and antimicrobial testing. The document is structured into sections that cover the epidemiology and etiology of bacteremia, stratified according to the various patient populations, and the diagnostic work-up, therapy, and follow-up of patients with bacteremia. Diagnostic and therapeutic decisions are presented as recommendations based on the grade of available scientific evidence.

First notification of positive blood cultures and the high accuracy of the gram stain report

When blood cultures turn positive, the attending physicians are usually notified immediately about Gram stain findings. However, information on the accuracy of Gram staining is very limited. We examined the accuracy of preliminary blood culture reports provided by a regional laboratory in an observational study including the years 1996, 2000 to 2001, and 2003. We used data from computer files and technicians' laboratory notes. The study was restricted to cultures with one morphological type. Using cultural identification as a reference, we estimated the sensitivity, specificity, and positive and negative predictive values (PPV and NPV, respectively) for the following defined morphological groups: gram-positive cocci in clusters, gram-positive cocci in chains or diplococci, gram-positive rods, gram-negative cocci, gram-negative rods, and yeasts. We further evaluated the Gram stain and wet mount findings for the most frequent bacterial species/groups. We obtained 5,893 positive blood cultures and the following results for the defined groups: sensitivity, range of 91.3 to 99.7%; specificity, 98.9 to 100%; PPV, 94.6 to 100%; and NPV, 99.0 to 100%. The sensitivity for the most frequent species was in the range 91.3 to 100%, with nonhemolytic streptococci having the lowest value (sensitivity, 91.3%; 95% confidence interval, 86.2 to 94.9%). Wet mount reports were less accurate (sensitivity of 30 to 70% for species with peritrichous motility), and Enterobacteriaceae (notably Salmonella spp.) accounted for 25% of the reports stating polar motility. In conclusion, we demonstrated a high accuracy of Gram stain reports, whereas wet mount microscopy was generally less accurate.

Burden of community-onset bloodstream infection: a population-based assessment

Although community-onset bloodstream infection (BSI) is recognized to be a major cause of morbidity and mortality, there is a paucity of population-based studies defining its overall burden. We conducted population-based laboratory surveillance for all community-onset BSI in the Calgary Health Region during 2000-2004. A total of 4467 episodes of community-onset BSI were identified for an overall annual incidence of 81.6/100,000. The three species, Escherichia coli, Staphylococcus aureus, and Streptococcus pneumoniae were responsible for the majority of community-onset BSI; they occurred at annual rates of 25.8, 13.5, and 10.1/100,000, respectively. Overall 3445/4467 (77%) episodes resulted in hospital admission representing 0.7% of all admissions to major acute care hospitals. The subsequent hospital length of stay was a median of 9 (interquartile range, 5-15) days; the total days of acute hospitalization attributable to community-onset BSI was 51,146 days or 934 days/100,000 annually. Four hundred and sixty patients died in hospital for a case-fatality rate of 13%. Community-onset BSI is common and has a major patient and societal impact. These data support further efforts to reduce the burden of community-onset BSI.

Macrophage serum markers in pneumococcal bacteremia: Prediction of survival by soluble CD163

OBJECTIVE

Soluble CD163 (sCD163) is a new macrophage-specific serum marker. This study investigated sCD163 and other markers of macrophage activation (neopterin, ferritin, transcobalamin, and soluble urokinase plasminogen activator receptor [suPAR]) as prognostic factors in patients with pneumococcal bacteremia.

DESIGN

Observational cohort study.

SETTING

Five university hospitals in Denmark.

PATIENTS

A total of 133 patients with Streptococcus pneumoniae bacteremia (positive blood culture) and 133 age- and gender-matched controls.

INTERVENTIONS

Samples were collected for biochemical analyses at the time of first positive blood culture.

MEASUREMENTS AND MAIN RESULTS

sCD163 was highly correlated with other macrophage markers and was significantly elevated (median [25-75 percentiles], 4.6 mg/L [2.8-8.9]) compared with healthy controls (2.7 mg/L [2.1-3.3], p < .0001). Increased levels were observed in patients who needed intensive care (hemodialysis, p = .0011; hypotension, p = .0014; mechanical ventilation, p = .0019). Significantly lower levels of sCD163, ferritin, transcobalamin, and suPAR (but not C-reactive protein) were measured in patients > or =75 yrs. In patients <75 yrs, all macrophage markers were increased in patients who died from their infection compared with survivors, whereas no change was observed in any of the markers in the very old age. At cutoff levels of 9.5 mg/L (sCD163) and 1650 nmol/L (C-reactive protein), the relative risk for fatal outcome in patients <75 yrs was 10.1 (95% confidence interval 3.4-31.0) and 7.0 (95% confidence interval 2.4-21.6) for sCD163 and C-reactive protein, respectively. In a multivariate logistic regression model for patients <75 yrs, ferritin, transcobalamin, neopterin, and suPAR contained no significant information on the probability of survival when sCD163 and CRP were known (p = .25).

CONCLUSIONS

Macrophage marker response in pneumococcal bacteremia was compromised in old age. In patients <75 yrs old, sCD163 was superior to other markers, including C-reactive protein, in predicting fatal disease outcome.

Incidence and prognosis of non-typhoid Salmonella bacteraemia in Denmark: a 10-year county-based follow-up study

The aim of this study was to examine the incidence and prognosis of non-typhoid Salmonella bacteraemia in a well-defined population in which complete follow-up investigations had been performed. All patients with non-typhoid Salmonella bacteraemia from 1994 through 2003 in North Jutland County, Denmark, were eligible for the study. Annual incidence rates were calculated for 10-year age groups. The North Jutland County Bacteraemia Database (inclusion of subjects), medical hospital records, the Prescription Registry (redemption of prescription drugs), and the Central Population Registry (deaths) were used as data sources. The outcomes were mortality within 30 and 180 days of the first non-typhoid-Salmonella-positive blood sample. Cox proportional-hazards regression analysis was performed, first with age and comorbidity as evidenced by Charlson index scores, and second with selected clinical and laboratory prognostic variables potentially related to non-typhoid Salmonella bacteraemia per se. A total of 111 non-typhoid Salmonella bacteraemia patients were included in the study. The incidence rate (mean 2.3/100,000 person-years) increased steadily from 1.9/100,000 person-years in the 40-49-year age group to 14.6/100,000 person-years in those >90 years. Twelve (11%) and 24 (22%) patients died within 30 and 180 days, respectively. Cox regression analyses showed that increasing age and, to a higher degree, increasing levels of comorbidity were independently associated with an unfavourable outcome, whereas none of the clinical or laboratory variables studied were strong independent prognostic factors. In conclusion, the presence of comorbid diseases and old age were independently associated with mortality, whereas clinical and laboratory variables were less important.

Direct identification of major blood culture pathogens, including Pseudomonas aeruginosa and Escherichia coli, by a panel of fluorescence in situ hybridization assays using peptide nucleic acid probes

Rapid identification of four major pathogens from 1,231 positive blood cultures by fluorescence in situ hybridization with peptide nucleic acid probes (AdvanDx Inc., Woburn, Mass.) was evaluated. For Escherichia coli, Staphylococcus aureus, and Candida albicans results agreed with conventional identification. The lower sensitivity of the Pseudomonas aeruginosa assay should not compromise the utility of the four assays.