Clinical implications of positive blood cultures

Intrinsic values of procalcitonin in bacterial bloodstream infections in people aged 75 years and over: a retrospective study

OBJECTIVE

To evaluate PCT measurement in the diagnosis of bloodstream infection (BSI) in hospitalized patients aged 75+.

METHOD

Descriptive, retrospective, monocentric study conducted in France, in patients with at least one blood culture and PCT and CRP measurements within the 24 hours before or after blood culture.

RESULTS

The mean PCT and CRP values for the 118 (15.2%) positive blood cultures were 18.90 ng/ml [95%CI: 0.007-334.7] and 153.93 mg/l [1-557], respectively. With a threshold of 0.3 ng/ml, PCT measurement had a sensitivity of 84%, a specificity of 53%, a PPV of 24%, and an NPV of 95%, making it possible to rule out BSI in 350 (45.1%) patients (α-risk=5%).

CONCLUSION

PCT measurement may eliminate BSI diagnosis more quickly than does blood culture reducing the inadequate and detrimental use of antibiotic therapy. A prospective study is required to validate its usefulness and confirm the cut-off value in geriatric populations.

Characteristic and outcomes of human and animal bites in Malawi

INTRODUCTION

Bites are an important contributor to traumatic injury worldwide. In low- and middle-income countries, data regarding bite injuries outside of rabies is limited. Therefore, we sought to describe the injury characteristics and outcomes of bites in Lilongwe, Malawi, and determine risk factors for animals and human bites.

METHODS

We performed a retrospective analysis of the Kamuzu Central Hospital trauma registry from 2008-2018. We performed Bivariate analyses comparing bite to non-bite trauma and human to animal bites. Multivariable Poisson regression modeling then estimated risk factors for bites.

RESULTS

A total of 124,394 patients were captured by the registry, of which 3,680 (3%) had a bite injury mechanism. Human bites accounted for 14.5% of bite injuries, and animals represented the remaining 85.5%. In rare cases, animal bite victims had serious complications, such as amputation (n = 6, 0.2%), orthopedic procedures (n = 5, 0.2%), and death (n = 7, 0.2%). Risk factors for an animal bite included being on a farm, field, or lake and being at home, whereas risk factors for a human bite included alcohol use and being at home.

CONCLUSION

Animal bite injuries in Malawi can confer a risk of serious complications, such as amputation and, in rare cases, death. Alcohol-associated, in-home interpersonal violence is a significant risk factor for human bite injuries. Further studies are needed to identify risk factors for complications and mortality.

What can we learn from supermarkets? An application of the Poisson distribution (order-up-to) model to improve blood culture bottle supplies

Background

The order-up-to inventory model is a method for identifying and maintaining the optimal product level for items that that hold value over time and have recurring demand. Typically, supermarkets utilise it to manage stock-levels of non-perishable goods.

Local problem

This project aimed to improve blood culture bottle supplies following reports by junior doctors of shortages when dealing with septic/unwell patients.

Methods

Data regarding blood culture bottle use was acquired from four hospitals within one trust in London (245 wards). The mathematical 'order-up-to' inventory model (an iterative Poisson distribution) was applied to the 6 months' data.

Interventions

The model found three predictable levels of demand to stock wards with no shortages in 99.3% of circumstances (based on historical data). Wards were stocked with blood culture bottles as per their required demand.

Results

A collection method and infrastructure was designed to implement the new policy and was applied to a London tertiary centre. A review of doctors, nurses and ward-managers found significant improvements in supply with no shortages since the model was applied. Issues with the dataset were identified for intensive therapy unit / high dependency unit.

Conclusions

The 'order-up-to' inventory model provides a useful tool within hospitals for improving stock levels of blood cultures bottles and with that the satisfaction of trainees and patient safety.

Does early bloodstream infection pose a significant risk of in-hospital mortality in adults with burns?

BACKGROUD/PURPOSE

Bloodstream infections (BSI) are common in patients with major burns, but its effect on mortality remains controversial. This study was aimed to investigate if BSI is significant risk factor of mortality?

METHODS

This is a retrospective chart review study included 266 adult patients admitted to our burn center from 2000 to 2019. Age, sex, inhalation injuries, total burn surface area (TBSA), duration of stay in intensive care unit, BSI and mortality were variables studied. Fisher exact test, Mann-Whitney test and logistic regression was used for statistical analysis.

RESULTS

There were 234 survivors and 32 non-survivors. Male was predominant. The overall incidence of BSI was 18.8%, and the overall crude mortality was 12%. Burns ≥30% TBSA and BSI were significant risk factors. A predictive function based on30% TBSA and BSI within 14 days after the onset of burns (BSI-14) was derived. The function has a sensitivity of 0.97, specificity of 0.42 and achieved a maximum Youden Index at functional value ≥0.05727. The mortality probability of BSI-14 in burns ≥30% TBSA was 40.8%.

CONCLUSIONS

BSI and burns ≥30% TBSA were significant risk factors of mortality. Early detection of BSI-14 is critical in burn care as its probability of mortality can be as high as 40% in patients ≥30% TBSA of burns. To reduce the risk of mortality, early in ventilator withdrawal, invasive lines and tubes removal, and early grafting should be emphasized besides infection control and appropriate use of antibiotics.

Comparison of the Clinico-Microbiological Characteristics of Culture-Positive and Culture-Negative Septic Pulmonary Embolism: A 10-Year Retrospective Study

Septic pulmonary embolism (SPE) is a rare yet serious infectious disorder with nonspecific clinical findings due to microorganism-containing emboli disseminating from extrapulmonary infectious foci. It is unknown whether a positive blood culture correlates with a worse clinical outcome. We compared the clinical and microbiologic characteristics of patients with SPE divided into the culture-positive group and the culture-negative one. This study was a retrospective observational study of the patients diagnosed with SPE and treated in an academic hospital from April 2010 to May 2020. We identified six culture-positive and four culture-negative patients with SPE during the study period. The culture-positive group had significantly longer periods of hospitalization (median: 75 days, range: 45-125 days) than the culture-negative group (median: 14.5 days, range: 3-43 days) (p < 0.05), as well as significantly elevated serum C-reactive protein and procalcitonin. Patients with culture-negative SPE more commonly had odontogenic infections as the primary infectious foci. Our study highlights the importance of giving extra attention to SPE patients who have a positive blood culture, as they may have worse clinical outcomes. Physicians need to collaborate with dentists when faced with patients with culture-negative SPE, since they may have primary odontogenic infections.

Ecology of Bloodstream Infections and Temporal Trends of Their Antibiograms with Respect to Source and Duration of Incubation: A 5-Year Retrospective Observational Analysis

Purpose  Blood is one of the most important connective tissues of human body. Bloodstream infection can range from inapparent bacteremia till fulminant septic shock with high mortality. Presence of microbes in blood whether continuously, intermittently, or transiently is a grave risk to every organ of body. Culture of blood is a vital tool to diagnose such infections. Drug susceptibility patterns help in rationalizing therapy. Objective  The aim of the study is to perform bacteriological analysis and assess drug sensitivity patterns of blood culture isolates and compare in light of other associated variables. Design  Retrospective observational study was conducted from January 2009 to December 2013 at a tertiary care hospital at Shillong, India. Blood samples were collected with aseptic guidelines and cultured for 7 days. Growths were identified by standard biochemical tests and subjected to sensitivity testing according to Modified Kirby Bauer disk diffusion method. Data for source of blood collection and duration of incubation were noted and compared. Results  A total of 658 (11.2%) pathogens were isolated from 5,867 bacteremia-suspected patient blood specimens. Contamination was observed at the rate of 1.21%. Gram-negative organisms were the predominant pathogens recovered, Klebsiella pneumoniae being the most common. No significant difference was observed between the number of organisms isolated within or beyond 48 hours. Acinetobacter baumannii and K. pneumoniae have significantly higher chances ( p < 0.05) of isolation from central line catheters compared with peripheral venipuncture. Conclusion  Successful treatment of sepsis depends on early diagnosis and proper antimicrobial therapy. Local knowledge of bacteriological profile and antimicrobial sensitivity patterns helps rationalize empiric treatment strategies.

Clinical experience in management of bloodstream infection in emergency medical ward: A preliminary report

Background:

Bloodstream infection is a life-threatening clinical condition posing significant morbidities and mortalities. An “Emergency Critical Care Management Program” has been implemented in the Emergency Medicine Ward at North Lantau Hospital as a pilot critical care service model in the local emergency medicine wards. Patients with blood stream infection are recruited in the program and managed under pre-defined guideline.

Objectives:

We report our experience in managing patients with blood stream infection in the Emergency Medicine Ward and analyzed their clinical outcomes.

Methods:

This was a retrospective cohort study including a total of 64 patients with blood stream infection admitted to the Emergency Medicine Ward from 1 March 2015 and 31 March 2018. Patients’ characteristics, microbiology, and risk factors associated with adverse outcomes including in-hospital mortality were analyzed.

Results:

The most common organism isolated from blood cultures was Escherichia coli (56%). Eight patients were transferred to the tertiary hospital. The overall in-hospital mortality was 7.8% (5/64). From the univariate analysis, advanced age (p < 0.001), higher Sequential Organ Failure Assessment score and quick Sequential Organ Failure Assessment score (p < 0.001), higher Charlson Comorbidity Index (p = 0.003), more organ dysfunction (p < 0.001), pre-existing medical history of chronic liver disease (p = 0.001), dysfunction in respiratory system (p = 0.032), cardiovascular system (p = 0.044) and the central nervous system (p < 0.001), presence of septic shock (p = 0.004), and need for higher level of organ support from the use of inotropes (p < 0.001) and mechanical ventilation (p = 0.024) were associated with in-hospital mortality. In the subgroup analysis, the in-hospital mortality rate for the patients with Sequential Organ Failure Assessment score less than 6 was 1.56% (1/64). Among the five in-hospital mortality cases, four of them were managed in the Emergency Medicine Ward under the End-of-Life Care Program. Decision for withholding and withdrawing life-sustaining therapy was made with the patients’ families.

Conclusion:

This preliminary report demonstrated that with careful patient selection, adoption of guidelines, and availability of expertise, critical care service can be safely implemented in the emergency medicine ward.

The correct blood volume for paediatric blood cultures: a conundrum?

BACKGROUND

Bloodstream infections (BSIs) are a major cause of morbidity and mortality in paediatric patients. For fast and accurate diagnosis, blood culture (BC) is the reference standard. However, the procedure for blood sampling in paediatric patients, particularly the optimal blood volume, is the subject of controversy stemming from a lack of knowledge of the bacterial load and because of several obstacles such as low intravascular volume and the risk of causing anaemia.

AIMS

The aim of this narrative review is to summarize current knowledge on blood sampling in paediatric patients for BC purposes, in particular blood volume and number and type of BC bottles needed for reasonable future guidelines/recommendations.

SOURCES

A comprehensive literature search of PubMed, including all publications in English, was performed in June 2019 using the search terms 'blood culture', 'blood volume', 'bloodstream infection', 'diagnostic', 'paediatric' and/or 'sepsis'.

CONTENT

The amount of inoculated blood determines the sensitivity, specificity and time to positivity of a BC, and low-level bacteraemia (≤10 cfu/mL) in paediatric patients is presumed to be more common than reported. Current approaches for 'adequate' blood volume for paediatric BC are mainly weight- or age-dependent. Of these recommendations, the scheme devised by Gaur and colleagues seems most appropriate and calls for a sample of 1-1.5 mL for children weighing <11 kg and 7.5 mL for a patient weight of 11-17 kg to be drawn into one BC bottle. Inclusion of a more detailed grading in the weight range 4-14 kg, as published by Gonsalves and colleagues, might be useful.

IMPLICATIONS

This review could be important for future guidelines on paediatric BC collection and thus could contribute to improving patient management and lowering the economic and global health burden associated with BSI. Furthermore, upcoming molecular-based approaches with low sample volumes might be an interesting alternative.

A Guide to Bacterial Culture Identification And Results Interpretation

PURPOSE

To provide a guide to interpreting bacterial culture results.

METHODS

Studies were identified via a PubMed literature search (from 1966 to January 2018). Search terms included microbial sensitivity tests, microbial drug resistance, and anti-infective agents/pharmacology. Articles were included if they were published in English. References within identified articles were also reviewed.

RESULTS

This paper reviewed core concepts of interpreting bacterial culture results, including timing of cultures, common culture sites, potential for contamination, interpreting the Gram stain, role of rapid diagnostic tests, conventional antibiotic susceptibility testing, and automated testing.

CONCLUSION

This guide can assist pharmacists in their role as integral members of the antimicrobial stewardship team in an effort to improve patient care.

Identifying Potentially Avoidable Hospitalizations in Medicare Patients With Prostate Cancer: A Retrospective Analysis

PURPOSE:

If identifiable, potentially avoidable hospitalizations (PAHs) can serve as an important target for cost containment efforts in oncology.

METHODS:

PAHs among a cohort of Medicare patients with prostate cancer were identified using a two-stage consensus-driven review process. In stage 1, two clinicians independently evaluated admissions records using a case review form, which we modified from a previous study to assess for PAHs. In stage 2, any admissions that the reviewers disagreed on or were unsure of were re-examined in a larger group of clinicians to yield a consensus determination regarding avoidability. Univariable and multivariable regression analyses were performed to identify factors predictive of PAH.

RESULTS:

There were 160 admissions among this cohort of 210 patients from January 2012 to June 2015, of which 99 were evaluable. Consensus-driven clinical review yielded an overall PAH rate of 28.3%. Factors associated with increased PAH risk were admission for symptoms related to cancer (odds ratio [OR], 7.33; P < .001), presence of a social contributor to admission (OR, 4.40; P = .014), and history of alcohol or drug abuse (OR, 4.93; P = .025). Admission for a noncancer condition was associated with decreased PAH risk (OR, 0.32; P = .011). On multivariable analysis, presence of a social contributor to admission (OR, 9.35; P = .002) and admission as a result of a noncancer condition (OR, 0.16; P = .038) remained predictive of PAH risk.

CONCLUSION:

A significant proportion of hospitalizations among patients with prostate cancer are potentially avoidable. Understanding factors predictive of risk for PAH can help inform programs aimed at avoiding such admissions to improve overall care quality and value.

Adequate or Inadequate? The Volume of Blood Submitted for Blood Culture at a Tertiary Children's Hospital

The volume of blood sampled for culture critically influences the results. This study aimed to determine (1) the volume of blood submitted for culture, (2) the proportion of blood cultures with adequate volume, (3) whether measured improvement from a previous educational intervention had been sustained, and (4) the impact of blood volume on culture result. The volume of blood submitted for cultures was determined over a 13-month period by weighing bottles before and after collection and before and after an educational intervention. The volume of blood submitted in 5127 culture bottles were measured. Fewer than 50% of all cultures were deemed adequate. A significant pathogen was isolated in 4.7% of blood cultures, and low-volume cultures were more likely to yield contaminant isolates (47/2422 [1.9%] vs 22/2705 [0.8%], P = .0005). Subsequently, the higher rate of contaminant isolates from low-volume cultures may affect selection and rationalization of antibiotic therapy.

Effect of a training programme on blood culture contamination rate in critical care

Blood culture contamination can occur from extraction to processing; its rate should not exceed 3%.

OBJECTIVE

To evaluate the impact of a training programme on the rate of contaminated blood cultures after the implementation of sample extraction recommendations based on the best evidence.

METHOD

Prospective before-after study in a polyvalent intensive care unit with 18 beds. Two phases were established (January-June 2012, October 2012-October 2015) with a training period between them. Main recommendations: sterile technique, surgical mask, double skin disinfection (70° alcohol and 2% alcoholic chlorhexidine), 70° alcohol disinfection of culture flasks and injection of samples without changing needles. Including all blood cultures of patients with extraction request.

VARIABLES

demographic, severity, pathology, reason for admission, stay and results of blood cultures (negative, positive and contaminated). Basic descriptive statistics: mean (standard deviation), median (interquartile range) and percentage (95% confidence interval). Calculated contamination rates per 100 blood cultures extracted. Bivariate analysis between periods.

RESULTS

Four hundred and eight patients were included. Eight hundred and forty-one blood cultures were taken, 33 of which were contaminated. In the demographic variables, severity, diagnosis and stay of patients with contaminated samples, no differences were observed from those with uncontaminated samples. Pre-training vs post-training contamination rates: 14 vs 5.6 per 100 blood cultures extracted (P=.00003).

CONCLUSION

An evidence-based training programme reduced the contamination of samples. It is necessary to continue working on the planning of activities and care to improve the detection of pollutants and prevent contamination of samples.

Interpretation and Relevance of Advanced Technique Results

Advanced techniques in the field of diagnostic microbiology have made amazing progress over the past 25 years due largely to a technological revolution in the molecular aspects of microbiology [1, 2]. In particular, rapid molecular methods for nucleic acid amplification and characterization combined with automation in the clinical microbiology laboratory as well as user-friendly software and robust laboratory informatics systems have significantly broadened the diagnostic capabilities of modern clinical microbiology laboratories. Molecular methods such as nucleic acid amplification tests (NAATs) rapidly are being developed and introduced in the clinical laboratory setting [3, 4]. Indeed, every section of the clinical microbiology laboratory, including bacteriology, mycology, mycobacteriology, parasitology, and virology, has benefited from these advanced techniques. Because of the rapid development and adaptation of these molecular techniques, the interpretation and relevance of the results produced by such molecular methods continues to lag behind. The purpose of this chapter is to review, update, and discuss the interpretation and relevance of results produced by these advanced molecular techniques.

Effect of Clinical Variables on the Volume of Blood Collected for Blood Cultures in an Adult Patient Population

OBJECTIVE To identify clinical variables that influence blood culture volume recovery DESIGN Retrospective chart review and linear model analysis SETTING A 621-bed Academic Medical Center with a Clinical Laboratory that processes 20,000+ blood cultures annually and dedicated phlebotomy staff for venipuncture PATIENTS Consecutive patients requiring blood culture METHODS Over a 6-day period, blood volume was determined in 568 culture bottles from 128 unique adult patients, and clinical data from the time of phlebotomy were extracted from hospital electronic medical records. Conditional hierarchical linear models with random effects for patient and phlebotomy occasion were utilized to analyze correlations between values collected from the same patient and during the same phlebotomy occasion. RESULTS Blood samples obtained from a central venous catheter yielded, on average, 2.53 mL more blood (95% CI, 1.63-3.44 mL; P<.001) than those from peripheral venipuncture, and aerobic bottles contained 0.38 mL more blood (95% CI, 0.1-0.67 mL; P=.009) than the anaerobic bottles. The remaining clinical variables (eg, hospital department, patient age, body mass index, gender, mean arterial pressure, concomitant systemic antibiotic use, and Charlson comorbidity index score) failed to reach statistical significance (P<.05) in relation to volume. CONCLUSIONS Blood cultures obtained from central venous catheters contain significantly greater volume than those obtained via peripheral venipuncture. These data highlight the clinically significant issue of low culture volume recovery, indicate that diagnostic and prognostic tools that rely on volume-dependent phenomena (ie, time to positivity) may require further validation under usual clinical practice circumstances, and suggest goals for future institutional performance improvement. Infect Control Hosp Epidemiol 2017;38:1493-1497.

Results of an early intervention programme for patients with bacteraemia: analysis of prognostic factors and mortality

Background

Bacteraemia is a common cause of morbidity and mortality in patients admitted to hospital. The aim of this study is to analyse the results of a two-year programme for the early optimisation of antibiotic treatment in patients admitted to the Costa del Sol Hospital (Marbella. Spain).

Methods

A prospective two-year cohort study was conducted, evaluating all episodes of bacteraemia at the Costa del Sol Hospital. Epidemiological and microbiological characteristics, any modification of the initial antibiotic treatment, prognostic risk stratification, early mortality related to the episode of bacteraemia, and mortality after the seventh day, were included in the analysis.

Results

Seven hundred seventy-three episodes of bacteraemia were treated, 61.6% males and 38.4% females. The mean age was 65.2 years. The condition was most commonly acquired in the community (41.4%). The bacteraemia was most frequently urological in nature (30.5%), and E coli was the microorganism most frequently isolated (31.6%). In 51.1% of the episodes, a modification was made to optimise the treatment. In the first week, 8.2% died from bacteraemia, and 4.5% had died when they were located. The highest rates of death were associated with older patients, nosocomial acquisition, no source, McCabe score rapidly fatal, Charlson index ≥3, Pitt index ≥3 and treatment remained unmodified.

Conclusion

The existence of bacteraemia control programmes and teams composed of clinicians who are experienced in the treatment of infectious diseases, can improve the disease outcome by enabling more severe episodes of bacteraemia to be recognised and their empirical treatment optimised.

Diagnostic Yield of Timing Blood Culture Collection Relative to Fever

BACKGROUND

Conventional practice involves obtaining a blood culture during or immediately after a fever to increase diagnostic yield. There are no data to support this practice in children.

METHODS

Retrospective single-center case-control study of children (0-18 years) who had blood cultures performed as part of routine care. Cases had an a priori defined pathogen isolated from blood culture (n = 410) and were age-matched with contemporaneous controls with a sterile blood culture (n = 410). The predictive value of fever (before and after blood culture), C-reactive protein and hematologic indices were analyzed by multivariate regression and area under the receiver operating characteristic curves (AUCs) in neonatal, general pediatric and pediatric oncology patients.

RESULTS

One thousand one hundred seventy-two (6.7%) of 17,607 blood cultures were positive, of which 410 (35%) cultured pathogen(s). Three hundred and twenty four (79%) cases and 275 (67.1%) controls had a fever (≥37.5°C) during the 12 hours pre- or post-collection. Fever 2-6 hours before a blood culture was neither sensitive nor specific for predicting bacteremia in neonatal or pediatric patients and marginally predictive in oncology patients (AUC 0.59-0.63). Cultures obtained 2-6 hours before fever were nonpredictive in neonates (AUC 0.56-0.59), marginally predictive in pediatric patients (AUC 0.64-0.67) and moderately predictive in oncology patients (AUC 0.70). C-reactive protein was marginally predictive in neonates (AUC 0.60). Hematologic indices were nonpredictive in all groups.

CONCLUSIONS

Fever before obtaining blood culture was neither sensitive nor specific for culture positivity; timing of pediatric blood cultures relative to fever is unimportant. Bacteremia precedes a fever, but this is of limited clinical applicability.

Risk Factors for Nosocomial Bacteremia in a Large Spanish Teaching Hospital: A Case-Control Study

Objective:

Identify independent risk factors associated with the development of nosocomial bacteremia.

Design:

Exploratory, unmatched, case-control study.

Setting:

A 970-bed Spanish university hospital.

Patients:

All non-neutropenic adult patients with nosocomial bacteremia admitted during a 12-month period were eligible as cases. All adult non-neutropenic patients without nosocomial bacteremia were eligible as controls.

Results:

The incidence of bacteremia in the study population was 6.9/1000 admissions/ year. One hundred eighty cases and 180 controls were analyzed. Multivariate analysis (stepwise logistic regression techniques) identified seven risk factors independently associated with nosocomial bacteremia: age above 65 years; prior admission (within six months) to the hospital; underlying diseases that were ultimately or rapidly fatal; indwelling urethral catheter in place for more than three days; intravenous central lines or peripheral venous lines (if in place for more than four days); “high-risk surgery” (i.e., lower abdominal, cardiac or thoracic); and admission to an intensive care unit.

Conclusions:

Although five variables are not modifiable, the remaining two relate to the use and duration of devices. Our data give strong support for the value of testing strict guidelines for limiting vascular catheters and evaluating the need for prolonged urethral catheterization. If effective infection control measures are identified, we could target hospital-wide surveillance to patients whose risk factors are amenable to intervention.

Understanding Bacterial Isolates in Blood Culture and Approaches Used to Define Bacteria as Contaminants: A Literature Review

BACKGROUND

Interpretation of blood culture isolates is challenging due to a lack of standard methodologies for identifying contaminants. This problem becomes more complex when the specimens are from sick young infants, as a wide range of bacteria can cause illness among this group.

METHODS

We used 43 key words to find articles published between 1970 and 2011 on blood culture isolates and possible contaminants in the PubMed database. Experts were also consulted to obtain other relevant articles. Selection of articles followed systematic methods considering opinions from more than 1 reviewer.

RESULTS

After reviewing the titles of 3869 articles extracted from the database, we found 307 relevant to our objective. Based on the abstracts, 42 articles were selected for the literature review. In addition, we included 7 more articles based on cross-references and expert advice. The most common methods for differentiating blood culture isolates were multiple blood cultures from the same subject, antibiograms and molecular testing. Streptococcus pneumoniae, Hemophilus influenzae, Neisseria meningitidis and group A and B streptococcus were always considered as pathogens, whereas Bacillus sp., Diphtheroids, Propionibacterium and Micrococcus were commonly regarded as contaminants. Coagulase-negative staphylococci were the most frequent isolates and usually reported as contaminants unless the patient had a specific condition, such as long-term hospitalization or use of invasive devices (catheters).

CONCLUSIONS

Inaccurate interpretation of blood culture may falsely guide treatment and also has long-term policy implications. The combination of clinical and microbiological knowledge, patient's clinical history and laboratory findings are essential for appropriate interpretation of blood culture.

Correlation between mass and volume of collected blood with positivity of blood cultures

BACKGROUND

The collection of blood cultures is an extremely important method in the management of patients with suspected infection. Microbiology laboratories should monitor blood culture collection.

METHODS

Over an 8-month period we developed a prospective, observational study in an adult Intensive Care Unit (ICU). We correlated the mass contained in the blood vials with blood culture positivity and we also verified the relationship between the mass of blood and blood volume collected for the diagnosis of bloodstream infection (BSI), as well as we explored factors predicting positive blood cultures.

RESULTS

We evaluated 345 patients with sepsis, severe sepsis or septic shock for whom blood culture bottles were collected for the diagnosis of BSI. Of the 55 patients with BSI, 40.0% had peripheral blood culture collection only. BSIs were classified as nosocomial in 34.5%. In the multivariate model, the blood culture mass (in grams) remained a significant predictor of positivity, with an odds ratio 1.01 (i.e., for each additional 1 mL of blood collected there was a 1% increase in positivity; 95% CI 1.01-1.02, p = 0.001; Nagelkerke R Square [R(2)] = 0.192). For blood volume collected, the adjusted odds ratio was estimated at 1.02 (95% CI: 1.01-1.03, p < 0.001; R(2) = 0.199). For each set of collected blood cultures beyond one set, the adjusted odds ratio was estimated to be 1.27 (95% CI: 1.14-1.41, p < 0.001; R(2) = 0.221).

CONCLUSIONS

Our study was a quality improvement project that showed that microbiology laboratories can use the weight of blood culture bottles to determine if appropriate volume has been collected to improve the diagnosis of BSI.

Diagnosis of Fusarium Infections: Approaches to Identification by the Clinical Mycology Laboratory

Infections caused by the genus Fusarium have emerged over the past decades and range from onychomycosis and keratitis in healthy individuals to deep and disseminated infections with high mortality rates in immune-compromised patients. As antifungal susceptibility can differ between the different Fusarium species, identification at species level is recommended. Several clinical observations as hyaline hyphae in tissue, necrotic lesions in the skin and positive blood tests with fungal growth or presence of fungal cell wall components may be the first hints for fusariosis. Many laboratories rely on morphological identification, but especially multi-locus sequencing proves better to discriminate among members of the species complexes involved in human infection. DNA-based diagnostic tools have best discriminatory power when based on translation elongation factor 1-α or the RNA polymerase II second largest subunit. However, assays based on the detection of other fusarial cell compounds such as peptides and cell wall components may also be used for identification. The purpose of this review is to provide an overview and a comparison of the different tools currently available for the diagnosis of fusariosis.

The current concepts in management of animal (dog, cat, snake, scorpion) and human bite wounds

Animal and human bite wounds represent a significant global health issue. In the United States, animal and human bites are a very common health issue, causing significant morbidity and even, in rare scenarios, mortality. Most animal bite wounds in the United States are caused by dogs, with cat bites being a distant second. Human bite wounds constitute a dominant subset of all bite wounds. Several studies of bite wounds have reported improved outcomes with early diagnosis and immediate treatment. However, the available literature on the initial treatment provides a plethora of conflicting opinions and results. In this review, our aim was to identify and assess the current evidence on the management of animal (dog, cat, insects, scorpions, and snakes) and human bite wounds.

LEVEL OF EVIDENCE

Review article, level III.

Quality assurance in blood culture: A retrospective study of blood culture contamination rate in a tertiary hospital in Nigeria

BACKGROUND

Blood culture is a critical tool for diagnosing septicaemia. Quite frequently, contamination of blood sample poses a great challenge to accurate diagnosis. This study evaluated the rate of blood culture contamination in our hospital over a one-year period.

MATERIALS AND METHODS

It was a retrospective study of 1032 blood cultures carried out in a clinical laboratory of a tertiary hospital in North Central part of Nigeria between 2010 and 2011.

RESULTS

There were 730 blood cultures from paediatric and 302 adult patients. The overall yield was 22%; 107 out of the 730 were contaminated giving a contamination rate of 10.4%. Contamination rate was higher in children than in adult (11% vs 8%) specimen. These rates were much higher than the acceptable benchmark of 2-3%. The main contaminants were coagulase negative Staphylococcus, Bacillus species, Diphtheroids and Enterococcus species.

CONCLUSION

Contamination rate is high, and mainly due to normal skin flora, suggesting aseptic collection challenges as the main cause. We recommend a review of the entire process of blood collection for culture and analysis with a view to instituting appropriate quality assurance measures to reduce the contamination rate.

How to interpret the bile culture results of patients with biliary tract infections

BACKGROUND/GOALS

Bile is normally sterile, but the presence of organisms in the bile does not necessarily imply an active infection. We wonder what the significance of bile culture results on antibiotics choice in cholangitis with negative blood culture. The aim of this study was to compare organisms cultured from bile with those from blood in bacteremic biliary tract infection and to evaluate factors associated with concordance between blood and bile isolates.

METHODS

Between 2000 and 2010, 266 positive blood cultures with concomitant bile culture in bacteremic biliary tract infection were identified. Follow-up bile specimens obtained after negative conversion of blood culture and clinical recovery from acute infection were collected for supplementary analysis.

RESULTS

Of the 266 events, 258 showed positive bile culture. Of the 258 bile samples, 80 yielded the same organisms with blood, 129 showed partial agreement and 49 yielded completely different organisms with blood. Only the number of organism was found to be independently associated with concordance. Of the 529 organisms isolated from bile, 227 were found in blood and gram-negative organisms showed higher rate of coincidence than gram-positive organisms. Of the 84 follow-up bile sample, 94% showed persistent positive culture and higher rate of antibiotics resistance than initial bile culture.

CONCLUSIONS

More than half of the organisms isolated from bile, especially gram-positive organisms, are not likely to be true pathogens. But single organism cultured from bile has clinical significance. Routine follow-up bile culture in patients showing clinical improvement is not necessary.

[Results of an early intervention program for patients with bacteremia discharged from the Emergency Department]

BACKGROUND AND OBJECTIVE

Occult bacteremia represents 3% of blood cultures drawn in the Emergency Department. In most cases, the evolution is unknown. The aim of the study is to analyze the results obtained after implementation of an intervention program for these patients.

PATIENTS AND METHODS

We describe the results of an early intervention program for patients with bacteremia in the Emergency Department discharged at home, which was implemented in daily clinical activity in Costa del Sol Hospital in Marbella (Malaga). We analyze the epidemiological, microbiological, Charlson comorbidity index, Pitt bacteremia index and 30-day mortality.

RESULTS

During 15 months, 90 patients were located. The median age was 67 years. There was a predominance of males with 54 of cases (60%). The acquisition place was predominantly the community with 51 cases (56.6%), being the most frequent microorganism Escherichia coli with 31 cases (34.4%). The median Charlson index and the bacteremia Pitt index were 1. Thirty-eight of the cases required hospitalization (42.2%). Pitt bacteremia index>1 and exchange antibiotic treatment were the related variables with need for admission. One patient died (1.2%) and 6 patients could not be located (6.6%).

CONCLUSIONS

The implementation of programs of early identification and management of patients with bacteremia in Emergency Department discharged al home allows early recovery of patients who require hospital admission and antibiotic treatment optimization. In our series, mortality after early intervention was low (1.2%).

A risk stratification model of acute pyelonephritis to indicate hospital admission from the ED

OBJECTIVES

There are no guidelines regarding the hospitalization of female patients with acute pyelonephritis (APN); therefore, we performed a retrospective analysis to construct a clinical prediction model for hospital admission.

METHODS

We conducted a retrospective analysis of a prospective database of women diagnosed as having APN in the emergency department between January 2006 and June 2012. Independent risk factors for admission were determined by multivariable logistic regression analysis in half of the patients in this database. The risk of admission was categorized into 5 groups. The internal and external validations were conducted using the remaining half of the patients and 192 independent patients, respectively.

RESULTS

Independent risk factors for admission were age of 65 years or greater (odds ratio [OR], 2.62; 1 point), chill (OR, 2.40; 1 point), and the levels of segmented neutrophils greater than 90% (OR, 2.00; 1 point), serum creatinine greater than 1.5 mg/dL (OR, 2.41; 1 point), C-reactive protein greater than 10 mg/dL (OR, 2.37; 1 point), and serum albumin less than 3.3 g/dL (OR, 7.36; 2 points). The admission risk scores consisted of 5 categories, which were very low (0 points; 5.9%), low (1 point; 10.7%), intermediate (2 points; 20.7%), high (3-4 points; 51.9%), and very high (5-7 points; 82.8%) risk, showing an area under the curve of 0.770. The areas under the curve of the internal and external validation cohorts were 0.743 and 0.725, respectively.

CONCLUSION

This model can provide a guideline to determine the admission of women with APN in the emergency department.

Interpretation and Relevance of Advanced Technique Results

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

A multicentre analysis of epidemiology of the nosocomial bloodstream infections in Japanese university hospitals

Nosocomial bloodstream infections (BSIs) are an important cause of morbidity and mortality. The current study analysed data from a concurrent surveillance programme to examine the current epidemiological trends for nosocomial BSIs at 22 Japanese university hospitals from 1 April 2008 to 31 March 2012. The number of blood culture sets taken, the rate of multiple blood culture sets and the rates of antibiotic-resistant isolates among six major nosocomial BSI pathogens (Staphylococcus aureus, Enterococcus spp., Escherichia coli, Klebsiella spp., Pseudomonas aeruginosa, and Candida spp.) not including coagulase-negative staphylococci, were evaluated. The clinical characteristics of nosocomial BSIs caused by these pathogens were also collected for 2941 patients. The number of blood culture sets taken per bed increased during the 4-year study period (from 4.07 in 2008 to 5.37 in 2011), and the rates of multiple blood culture sets also increased (from 29.9% in 2008 to 50.0% in 2011). Methicillin resistance was detected in 50.2% of S. aureus isolates. The prevalence rates of extended-spectrum beta-lactamase-producing E. coli and Klebsiella spp. isolates increased annually during the study period, and the average prevalence rates were 12.3% and 5.8%, respectively. The overall crude mortality of nosocomial BSIs due to the six pathogens evaluated was 24.5% (43.2% in ICU settings and 20.5% in non-ICU settings). Thus, our multicentre study evaluated the current epidemiological trends for nosocomial BSIs, and we found that further efforts are needed to increase the use of multiple blood culture sets and improve the prognosis of nosocomial BSIs in Japanese university hospitals.

Patient risk factors for outer membrane permeability and KPC-producing carbapenem-resistant Klebsiella pneumoniae isolation: results of a double case-control study

BACKGROUND

In the 1,200-bed university hospital "Umberto I" in Rome, Italy, we observed a dramatic substitution of a precedingly well-documented Klebsiella pneumoniae clone (ST37) with ertapenem resistance by outer membrane permeability modification (Porin-ER-Kp) with a new K. pneumoniae strain expressing carbapenem resistance due to K. pneumoniae carbapenemase production (KPC-CR-Kp). A case-case-control study was carried out to evaluate risk factors for Porin-ER-Kp and KPC-CR-Kp isolation.

METHODS

All patients with hospital-acquired K. pneumoniae isolation between July 2008 and June 2011 were included. Two case groups including patients harbouring KPC-CR-Kp and Porin-ER-Kp were analysed, with a third control group from whom carbapenem-susceptible K. pneumoniae (CS-Kp) were isolated.

RESULTS

Forty-four KPC-CR-Kp cases, 39 Porin-ER-Kp cases and 60 CS-Kp controls were analysed. During the 3-year study, a specific Porin-ER-Kp endemic clone (ST37) was substituted by a new KPC-CR-Kp clone (ST512). Breakthrough bacteraemias occurred in 21 out of 26 KPC-CR-Kp group bloodstream infections (BSIs); nine of these developed during carbapenem therapy and seven with colistin and/or tigecycline therapy. In 13 Porin-ER-Kp BSIs, breakthrough bacteraemias developed in eight patients and four during carbapenem therapy. In the multivariable analysis, KPC-CR-Kp isolates were associated with carbapenems [odds ratio (OR) 7.74; 95 % confidence interval (CI) 1.70-35.2; p < 0.01) and endoscopy (OR 6.71; 95 % CI 1.25-36.0; p < 0.03). Porin-ER-Kp independent risk factors included second-generation cephalosporins (OR 25.7; 95 % CI 3.20-206.8; p < 0.01), carbapenems (OR 19.1; 95 % CI 4.34-83.9; p < 0.001), acute renal failure (OR 7.17; 95 % CI 1.33-38.6; p < 0.03), endoscopy (OR 6.12; 95 % CI 1.46-25.6; p < 0.02) and third-generation cephalosporins (OR 5.3; 95 % CI 1.34-20.9; p < 0.02).

CONCLUSIONS

Porin-ER-Kp strains needed major antimicrobial pressure compared to KPC-CR-Kp to express resistance. KPC-CR-Kp substituted Porin-ER-Kp strains, causing more infections. KPC-CR-Kp breakthrough bacteraemia occurred even under therapy with tigecycline or colistin, underlining that an antibiotic stewardship programme is needed urgently.

Bacteremia in a long term care facility

Episodes of bacteremia identified in a long term care facility over a seven and a half-year period from July 1984 to December 1991 were reviewed. Twenty-nine episodes of bacteremia were identified, a rate of 4.35/100,000 patient-days. The most common infecting organisms were Escherichia coli (11 episodes), Streptococcus pneumoniae (four), Proteus mirabilis (three), Staphylococcus aureus (three) and Bacteroides species (two). The source of bacteremia was urinary in 45% of patients, gastrointestinal in 17%, pneumonia in 14%, skin in 14% and unknown in 10%. The overall case fatality rate was 24%, but for the final six years of the review the case fatality rate was only 9.5%. These observations report a rate of bacteremia 10-fold lower than reported from other North American long term care facilities and, potentially, a lower case fatality rate. The primary site of bacteremia, however, in long term care facilities is the urinary tract.

Comparative activity of cefepime with several antimicrobials against aerobic Gram-negative and Gram-positive organisms isolated from patients across Canada in 1993

To compare the activity of cefepime, a fourth-generation cephalosporin, with several available antimicrobials, in vitro susceptibility studies were carried out on bacteria commonly associated with various infections, including sepsis. Ten tertiary care hospital laboratories in six provinces provided 1276 clinically relevant isolates of aerobic Gram-negative bacilli and Gram-positive cocci during 1993. When the activity of each of the antimicrobials was determined against all isolates submitted, cefepime, piperacillin/tazobactam, imipenem and ciprofloxacin all had minimal inhibitory concentrations for 90% of the organisms (mic(90)) two or more dilutions below the mic resistant category. Gentamicin's mic(90) against all organisms tested was one dilution below the mic resistant category. The mic(90)s of the third-generation cephalosporins, piperacillin and ticarcillin/clavulanate, for Enterobacter species fell in the resistant category. This is presumably due to constitutive high level chromosomal cephalosporinase production. The mic(90)s of cefepime for Enterobacter species was three or more dilutions below the mic resistant category. The mic(90)s of all antimcrobials against Staphylococcus aureus, with the exception of ceftazidime and piperacillin, had mic(90) categories two or more dilutions below the resistant category. The activity of cefepime, piperacillin/tazobactam, imipenem, ciprofloxacin and gentamicin make them excellent candidates for the empirical therapy of serious infections due to aerobic Gram-negative bacilli and S aureus.

Diagnostic utilities of procalcitonin and C-reactive protein for the prediction of bacteremia determined by blood culture

BACKGROUND

We compared the diagnostic utilities of procalcitonin (PCT) and C-reactive protein (CRP) for predicting bacteremia diagnosed by blood cultures. PCT was also evaluated as a parameter for differentiating true bacteremia from culture contamination.

METHODS

We analyzed a total of 3343 patients in which PCT, CRP, and blood cultures were concurrently requested for detecting bacteremia from January 2010 to December 2011. PCT concentrations were measured by the VIDAS® Brahms PCT assay, and CRP concentrations were determined by a turbidimetric assay using CA-400 analyzer.

RESULTS

The PCT concentrations of bacteremia cases (n=331) were significantly higher than those of non-bacteremia (n=2856) (median: 3.2 ng/ml vs. 0.4 ng/ml, P<0.0001). The correlation coefficient between the PCT and CRP concentrations was 0.51. The areas under the receiver operating characteristic curves (ROC-AUCs) of PCT and CRP for discriminating bacteremia from non-bacteremia were 0.76 and 0.64, respectively. The ROC-AUC of PCT for differentiating true bacteremia from contamination was 0.86, while that of CRP was 0.65.

CONCLUSIONS

PCT concentration by single testing was more useful for predicting bacteremia than CRP. PCT also exhibited diagnostic utility for ruling out blood culture contamination. Thus, PCT could be helpful in the accurate diagnosis of bacteremia.

Comprehensive analysis of blood culture performed at nine university hospitals in Korea

Background

Optimal blood culture performance is critical for successful diagnosis and treatment of sepsis. To understand the status of blood culture, we investigated several aspects of the procedure at 9 university hospitals.

Methods

The process of ordering blood culture sets and sampling volume for adults and children was investigated from January 2010 to April 2010, while the positive rate of detection and growth of skin contaminants were compared in 2009. Microbial growth in aerobic and anaerobic bottles was investigated prospectively.

Results

A majority of the hospitals used 2 sets of bottles for adults and 1 bottle for children. The average blood volume in each set was 7.7 mL for adults and 2.1 mL for children. The positive rate of microorganisms was 8.0%, and the isolation rate of the normal flora of the skin was 2.1%. Bacterial growth rates in aerobic and anaerobic bottles only were 31.8% and 24.5% respectively.

Conclusions

Ordering blood culture sets and sampling volumes did not comply with CLSI guidelines. However, the rate of positive cultures and skin contamination rates were acceptable. Anaerobic bottles are useful in enhancing the yield of microorganisms.

[Clinical-microbiological management of blood cultures positive for coagulase-negative staphylococci]

A 53-year old male admitted for episodes of sustained ventricular tachycardia subjected to electrical cardioversion, carrier of a right femoral central venous catheter, began with febrile peaks, and Staphylococcus epidermidis was isolated in the blood cultures. What is the value of isolation in the blood cultures of S. epidermidis, a microorganism that forms a part of the usual flora of the skin and mucous of the patient? How should this situation be managed? Should an antimicrobial agent be administered? Which one? For how long?

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry identifies 90% of bacteria directly from blood culture vials

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is now widely used for marker/multi-biomarker detection in medical diagnosis. We tested a new protocol for bacterial identification from blood culture broths in hospital routine by using collection tubes with separator gels on 503 included samples examined over 3 months, where 1.5 mL was injected by a syringe into BD Vacutainer tubes from BACTEC-positive bottles, before processing for bacterial protein extraction. Samples were loaded in duplicate onto the MALDI MS target, allowing a series of 12 samples to be processed in duplicate within 80 min by using Biflex III and BioTyper 2.0 software (Bruker). Including polymicrobial samples, 193 of 213 of Gram-negative bacteria (91.08%) and 284 of 319 of Gram-positive bacteria (89.02%) were correctly identified at the species level. Enterobacteriaceae constituted 35.15% of all species found, Staphylococaceae 37.96%, Streptococaceae and Enterococaceae 20.85%, Pseudomonadaceae 1.69%, and anaerobes 2.44%. In most of the polymicrobial samples, one of the species present was identified (80.9%). Seven isolates remained misidentified as Streptococcus pneumoniae, all belonging to Streptococcus mitis. Staphylococcus aureus was identified better when grown on anaero-aerobic medium, and MALDI BioTyper identification scores as low as 1.4 were pertinent, provided that four successive proposals of the same species were given. This new protocol correlates with conventional microbiology procedures by up to 90%, and by >95% for only monomicrobial samples, and provides a decreased turn-around time for identification of bacteria isolated from blood cultures, making this technology suitable also for blood cultures, with less delay and cost decreases in bacterial diagnostics, and favouring better care of patients.

Bacterial identification by 16S rRNA gene PCR-hybridization as a supplement to negative culture results

PCR-hybridization was compared to culture methods for evaluating suspected blood infections. A total of 231 clinical samples from blood culture bottles that were flagged positive by the BacT/Alert system or were negative 1 week after inoculation were tested. When the PCR-hybridization and culture method results were compared, the positive and negative concordance rates were 99.2% (122/123) and 89.5% (94/105), respectively. Of the negative blood cultures, 10.5% (11/105) were positive by PCR-hybridization. Supplemental testing of negative blood cultures may identify bacterial pathogens that are undetectable by culture methods.

Conventional and molecular techniques for the early diagnosis of bacteraemia

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

Existing data sources for clinical epidemiology: The North Denmark Bacteremia Research Database

Bacteremia is associated with high morbidity and mortality. Improving prevention and treatment requires better knowledge of the disease and its prognosis. However, in order to study the entire spectrum of bacteremia patients, we need valid sources of information, prospective data collection, and complete follow-up. In North Denmark Region, all patients diagnosed with bacteremia have been registered in a population-based database since 1981. The information has been recorded prospectively since 1992 and the main variables are: the patient’s unique civil registration number, date of sampling the first positive blood culture, date of admission, clinical department, date of notification of growth, place of acquisition, focus of infection, microbiological species, antibiogram, and empirical antimicrobial treatment. During the time from 1981 to 2008, information on 22,556 cases of bacteremia has been recorded. The civil registration number makes it possible to link the database to other medical databases and thereby build large cohorts with detailed longitudinal data that include hospital histories since 1977, comorbidity data, and complete follow-up of survival. The database is suited for epidemiological research and, presently, approximately 60 studies have been published. Other Danish departments of clinical microbiology have recently started to record the same information and a population base of 2.3 million will be available for future studies.

Blood cultures: key elements for best practices and future directions

Bloodstream infections (BSI) cause significant morbidity and mortality among populations worldwide. Blood cultures (BCs) are regarded as the "gold standard" for diagnosis of bacteremia and are among the most important functions of the clinical microbiology laboratory. Significant changes in the methods and techniques of obtaining BCs have occurred since the first inception of BCs into clinical practice. Aside from significant improvements of established, conventional technology, new assays for diagnosis of bacteremia and fungemia, particularly those involving molecular techniques, are now available. BCs must be collected under sterile conditions and guidelines for appropriate collection, processing, and results reporting of BCs have been established. This review provides comprehensive information on optimal BC practices for laboratories, utilizing traditional approaches and emerging technology. As laboratories and clinicians must appreciate the key factors affecting the use of these techniques, improved communication between laboratory personnel and clinicians regarding such elements as duration of incubation, workup of contaminants and critical action value reporting will greatly improve the diagnostic approach to BSI.

New method for the detection of micro-organisms in blood: application of quantitative interpretation model to aerobic blood cultures

The physical and chemical changes occurring in blood that has been inoculated into a blood culture bottle can be used as means to detect the presence of microorganisms in blood cultures. These changes include primarily the conversion of oxy- to deoxyhemoglobin within the red blood cells (RBCs) and changes in the cell number densities. These changes in the physical and chemical properties of blood can be readily detected using spectrophometric methods thus enabling the continuous monitoring of blood culture vials to provide quantitative information on the growth behavior of the microorganisms present. This paper reports on the application of spectrophotometric information obtained from diffuse reflectance measurements of aerobic blood cultures to detect microbial growth and compares the results to those obtained using the standard blood culture system.

[Microorganisms isolated from blood cultures and their antimicrobial susceptibility patterns at a university hospital during 1994-2003]

BACKGROUND

Blood culture is important for the determination of the etiologic agent of bacteremia. Analysis of blood culture results and antimicrobial susceptibility trend can provide clinicians with relevant information for the empirical treatment of patients.

METHODS

The species and antimicrobial susceptibility of the isolates from blood cultures at the Severance Hospital during 1994-2003 were analysed. Blood specimens were cultured for 7 days using tryptic soy broth and thioglycollate medium. Identification of organism was based on conventional methods or commercial kit systems. Antimicrobial susceptibility was tested by a disk diffusion method.

RESULTS

Of 536,916 blood specimens cultured, 24,877 (4.6%) from 13,102 patients were positive. Among the isolates, 93.1% were aerobic or facultative anaerobic bacteria, 3.3% anaerobes, and 3.6% fungi. Escherichia coli was isolated most frequently, followed by Staphylococcus aureus, alpha-hemolytic Streptococcus, Enterococcus spp., and Klebsiella pneumoniae. The proportion of patients with Enterococcus faecium and K. pneumoniae gradually increased during this study. Enterococcus, S. aureus and alpha-hemolytic Streptococcus were frequently isolated from the age group of less than 2 yr. E. coli, Enterococcus spp., K. pneumoniae and S. aureus from the age group of over 50 yr. Oxacillin-resistant S. aureus decreased, whereas vancomycin-resistant E. faecium and imipenemresistant Pseudomonas aeruginosa and Acinetobacter baumannii increased.

CONCLUSIONS

E. coli was the most common cause of bacteremia and S. aureus, alpha-hemolytic Streptococcus, and K. pneumoniae were frequently isolated pathogens. The bacteremia due to Enterococcus, K. pneumoniae, fungi, vancomycin-resistant E. faecium, and imipenem-resistant P. aeruginosa and A. baumannii gradually increased during this period.

Timing of specimen collection for blood cultures from febrile patients with bacteremia

Bloodstream infections are an important cause of morbidity and mortality. Physician orders for blood cultures often specify that blood specimens be collected at or around the time of a temperature elevation, presumably as a means of enhancing the likelihood of detecting significant bacteremia. In a multicenter study, which utilized retrospective patient chart reviews as a means of collecting data, we evaluated the timing of blood culture collection in relation to temperature elevations in 1,436 patients with bacteremia and fungemia. The likelihood of documenting bloodstream infections was not significantly enhanced by collecting blood specimens for culture at the time that patients experienced temperature spikes. A subset analysis based on patient age, gender, white blood cell count and specific cause of bacteremia generally also failed to reveal any associations.