Empiric Antibiotic Selection Research Articles

Consequences of Combining Cystic Fibrosis— and Non-Cystic Fibrosis-Derived Pseudomonas aeruginosa Antibiotic Susceptibility Results in Hospital Antibiograms

In preparing hospital antibiograms for individual organisms and antibiotics, laboratories often combine susceptibility data for isolates from a variety of sources and patient types. If results from patients with known resistance patterns that vary from normal are included, the overall susceptibility value for the institution could be misleadingly skewed. To assess the degree of bias introduced into a hospital antibiogram by combining cystic fibrosis (CF) and non-CF isolates of Pseudomonas aeruginosa to produce one hospital-wide percent susceptible figure for each tested antibiotic. A retrospective analysis was conducted of an academic, tertiary care medical center's microbiology database. We examined quarterly and annual susceptibility data from 2004, comparing non-CF data with combined susceptibility data for 10 antibiotics within each quarter, as well as those reported in the annual antibiogram. Differences were assessed for statistical significance using chi(2) testing with Bonferroni correction. Large differences were observed between non-CF and combined percent susceptible data in the 4 quarters (aminoglycosides 3% vs 20%, fluoroquinolones 2% vs 18%, respectively) and when comparing annual non-CF (n = 191) with annual combined (n = 266) data. With the annual figures, these differences were frequently statistically significant (70% vs 58%, 91% vs 83%, 85% vs 70%, and 72% vs 60% for gentamicin, tobramycin, amikacin, and gatifloxacin/levofloxacin, respectively; all p< or =0.01). Combining CF and non-CF P. aeruginosa susceptibility into one percent susceptibility value for all isolates may produce figures that underestimate the activity of some antibiotic classes against non-CF isolates. Clinicians may make less than optimal empiric antibiotic selection choices based on such data.

Characteristics of community-acquired and health care-associated Staphylococcus aureus bacteremia in patients treated at the emergency department of a teaching hospital

The changing epidemiology of Staphylococcus aureus bacteremia has been noted worldwide. This enhanced awareness appears to be closely associated with the evolution of health care systems. To further delineate this change and to clarify the prevalence of true community-acquired methicillin-resistant S. aureus (MRSA), reclassification for community-onset bacteremia was proposed. Exposure to health care system, such as nursing home residence, regular outpatient invasive interventions, and prior hospitalization within 1 year, was identified among the community-onset S. aureus bacteremia patients. During the 1-year study period, 102 episodes of S. aureus bacteremia from the emergency department patients of a teaching hospital were prospectively enrolled. Nine of the episodes were hospital-acquired, 56 episodes were associated with health care system exposure, and the remaining 37 episodes were classified as true community-acquired bacteremia. The characteristics of patients, primary site of infection, antimicrobial susceptibilities of S. aureus isolates, adequacy of initial antimicrobial therapy, and percentage of metastatic infections differed significantly between health care-associated and true community-acquired S. aureus bacteremias. Prevalence of MRSA infection in true community-acquired bacteremia was low in contrast to bacteremia with health care-associated exposure (2.7% versus 42.9%, P < 0.01). In conclusion, clinical characteristics and risk of contracting methicillin-resistant S. aureus bacteremia among community patients with and without exposure to health care system are distinct. Precise classification of patients is mandatory for the surveillance of antimicrobial resistance and selection of rationale empirical antibiotics.

Optimization of empirical antibiotic selection for suspected Gram-negative bacteraemia in the emergency department

A 1-year prospective study of patients with a positive blood culture and admitted through the emergency department (ED), was conducted to detect incidence and risk factors for resistance of Enterobacteriaceae to gentamicin and ciprofloxacin. A total of 245 emergency department-admitted patients had positive blood cultures, of which 131 (54%) grew Enterobacteriaceae. Of these 131 isolates, 32 (24%) were resistant to gentamicin and 37 (28%) to ciprofloxacin. Risk factors, by multivariate analysis, for gentamicin and ciprofloxacin resistance were: male gender ( P < 0.05 and P < 0.01, respectively), nursing home residence ( P < 0.001), diabetes mellitus ( P < 0.05) and presence of a foreign body ( P < 0.05 and P < 0.005). An additional risk factor for ciprofloxacin resistance was recent hospitalisation ( P < 0.05). These data facilitate optimal selection of empirical antibiotic treatment of suspected Gram-negative infections, and may contribute to improved patient outcome and optimal use of antibiotics.

Optimum management of pediatric patients with fever and neutropenia.

Fever with neutropenia is a common clinical problem in patients receiving cancer treatment. Prevention and optimum management of infectious complications is critical to the overall success of cancer therapy. This article provides an overview of the current status of this evolving subject. While the basic principles of rapid institution of broad spectrum antibiotics, early intervention with empiric antifungal therapy and continuation of antimicrobials during period of risk are unlikely to change, there is increasing interest in titrating this aggressive approach based on the projected risk of the development of a serious invasive infection. Oral antibiotic therapy and outpatient management are currently being studied in pediatric oncology patients, but even when successful these alternatives to the traditional "in hospital, parenteral antibiotic therapy" approach are unlikely to be applicable in all patient populations and clinical settings. While there is no replacement for clinical acumen and careful monitoring, judicious use of diagnostic resources such as blood cultures and imaging studies is a key component of optimum care. Selection of empiric antibiotics based on ongoing monitoring of antimicrobial susceptibility patterns is emphasized.

Antibiograms: New NCCLS Guidelines, Development, and Clinical Application

Antibiograms are an important resource for health care providers. All clinicians involved in antibiotic selection and monitoring should become familiar with the NCCLS M39-A document “Analysis and Presentation of Cumulative Antimicrobial Susceptibility Test Data: Approved Guideline.” Providers who interpret and apply antibiogram data in clinical practice should know about susceptibility testing methods, the susceptibility breakpoint determination process, and problems associated with antibiogram data analysis. The M39-A guidelines contain more than 40 recommendations, including the following: antibiogram data should be analyzed at least annually, an attempt should be made to remove duplicate isolates, and only organisms with 10 isolates or more should be presented. Accurate antibiograms facilitate improved empiric antibiotic selection and more precise monitoring of bacterial resistance in the hospital. This article reviews common antimicrobial susceptibility testing methods and relevant issues, highlights the major NCCLS M39-A recommendations, discusses the antibiogram preparation process and challenges in data interpretation, and provides a general overview of how antibiogram data may be applied to clinical practice.

Comparison of microbial findings and resistance to antibiotics between transplant patients, patients on hemodialysis, and other patients with the diabetic foot

Infectious complications of the diabetic foot may be influenced by impaired renal function and by immunosuppression therapy. Aims: To assess differences in microbial findings and resistance to antibiotics between transplant recipients, hemodialysis patients, and other patients with the diabetic foot. Methods: 207 patients treated in the foot clinic for diabetic ulcers from 12/1998 to 12/1999 were included into this retrospective study. Patients were divided into three groups (transplant, dialysis, and other patients). Occurrence of individual bacterial species and resistance to antibiotics was compared between study groups. Results: Study groups did not differ significantly in ulcer grades defined by the Wagner classification or in the mean number of pathogens per patient. The prevalence of individual microorganisms did not differ between the study groups. However, the study groups differed significantly in the occurrence of microbial resistance to antibiotics. Transplant patients had more frequently Staphylococcus aureus resistant to oxacillin ( P<.01), imipenem ( P<.01), co-trimoxazole ( P<.01), Enterococcus species resistant to ampicillin ( P<.01), piperacillin ( P<.01), and dialysis patients had more frequently Pseudomonas species resistant to piperacillin ( P<.05) and cefpirom ( P<.05) in comparison with the other two groups. Conclusions: Transplant patients had significantly more resistant microorganisms in comparison with dialysis and other patients with the diabetic foot. Empiric antibiotic selection based on general population data should be modified in transplant patients with diabetic foot according to actual susceptibility to antibacterial drugs.

Prediction model to identify patients with Staphylococcus aureus bacteremia at risk for methicillin resistance.

To identify institution-specific risk factors for MRSA bacteremia and develop an objective mechanism to estimate the probability of methicillin resistance in a given patient with Staphylococcus aureus bacteremia (SAB). A cohort study was performed to identify institution-specific risk factors for MRSA. Logistic regression was used to model the likelihood of MRSA. A stepwise approach was employed to derive a parsimonious model. The MRSA prediction tool was developed from the final model. A 279-bed, level 1 trauma center. Between January 1, 1999, and June 30, 2001, 494 patients with clinically significant episodes of SAB were identified. The MRSA rate was 45.5%. Of 18 characteristics included in the logistic regression, the only independent features for MRSA were prior antibiotic exposure (OR, 9.2; CI95, 4.8 to 17.9), hospital onset (OR, 3.0; CI95, 1.9 to 4.9), history of hospitalization (OR, 2.5; CI95, 1.5 to 3.8), and presence of decubitus ulcers (OR, 2.5; CI95, 1.2 to 4.9). The prediction tool was derived from the final model, which was shown to accurately reflect the actual MRSA distribution in the cohort. Through multivariate modeling techniques, we were able to identify the most important determinants of MRSA at our institution and develop a tool to predict the probability of methicillin resistance in a patient with SAB. This knowledge can be used to guide empiric antibiotic selection. In the era of antibiotic resistance, such tools are essential to prevent indiscriminate antibiotic use and preserve the longevity of current antimicrobials.

Microbiology of bile in patients with cholangitis or cholestasis with and without plastic biliary endoprosthesis

Background: Cholangitis is a frequent complication of biliary stents. Empiric antibiotic selection is primarily based on bile cultures obtained from patients undergoing surgery and few data are available with respect to ERCP and biliary stents. This study analyzed the microbiology of bile and the antibiotic sensitivities of the organisms identified in patients presenting with clinical cholangitis or cholestasis. Methods: All bile cultures collected during ERCP from January 1994 to January 2000 were identified by using an ERCP database. Results: One hundred eighty cultures from 160 patients (mean age 55 years, range 6-94 years) were identified. Sixty-nine specimens were collected at ERCPs performed in patients with no biliary stent in place (group 1). One hundred eleven specimens were obtained from patients with a biliary stent in situ (group 2). The primary diagnoses for patients in groups 1 and 2 were as follows, respectively: malignant bile duct obstruction (25 and 85), choledocholithiasis (16 and 2), benign biliary strictures (6 and 18), acquired immunodeficiency syndrome (8 and 0), and miscellaneous (14 and 6). There were 38 positive bile cultures in group 1 (55%) and 109 positive cultures in group 2 (98%; p < 0.05). A higher frequency of polymicrobial infections (90%) was found in group 2 patients (vs. group 1, 45%; p < 0.001). Escherichia coli was the most common organism found in group 1 (17%); Enterococcus the most common in group 2 (31%). Among patients with positive bile cultures, bacteremia was more frequent in group 2 patients (46% vs. 21%; p < 0.05). Ciprofloxacin and cefiriaxone were the most effective antibiotics against identified gram-negative bacilli, and vancomycin against Enterococci. Conclusion: In patients with cholangitis associated with biliary obstruction, the antibiotic selected initially should be active against gram-negative bacilli. Use of quinolones is recommended because these agents effectively penetrate an obstructed biliary tree and can be administered orally. Enterococci and polymicrobial infections are found more commonly in patients with a biliary stent than those without a stent. Pending definitive biliary decompression, patients with sepsis and those who do not quickly respond to treatment with a quinolone may benefit from the addition of antibiotic coverage against gram-positive organisms, targeted against Enterococci. (Gastrointest Endosc 2002;56:885-9.)

Microbiology of bile in patients with cholangitis or cholestasis with and without plastic biliary endoprosthesis.

Cholangitis is a frequent complication of biliary stents. Empiric antibiotic selection is primarily based on bile cultures obtained from patients undergoing surgery and few data are available with respect to ERCP and biliary stents. This study analyzed the microbiology of bile and the antibiotic sensitivities of the organisms identified in patients presenting with clinical cholangitis or cholestasis. All bile cultures collected during ERCP from January 1994 to January 2000 were identified by using an ERCP database. One hundred eighty cultures from 160 patients (mean age 55 years, range 6-94 years) were identified. Sixty-nine specimens were collected at ERCPs performed in patients with no biliary stent in place (group 1). One hundred eleven specimens were obtained from patients with a biliary stent in situ (group 2). The primary diagnoses for patients in groups 1 and 2 were as follows, respectively: malignant bile duct obstruction (25 and 85), choledocholithiasis (16 and 2), benign biliary strictures (6 and 18), acquired immunodeficiency syndrome (8 and 0), and miscellaneous (14 and 6). There were 38 positive bile cultures in group 1 (55%) and 109 positive cultures in group 2 (98%; p < 0.05). A higher frequency of polymicrobial infections (90%) was found in group 2 patients (vs. group 1, 45%; p < 0.001). Escherichia coli was the most common organism found in group 1 (17%); Enterococcus the most common in group 2 (31%). Among patients with positive bile cultures, bacteremia was more frequent in group 2 patients (46% vs. 21%; p < 0.05). Ciprofloxacin and cefiriaxone were the most effective antibiotics against identified gram-negative bacilli, and vancomycin against Enterococci. In patients with cholangitis associated with biliary obstruction, the antibiotic selected initially should be active against gram-negative bacilli. Use of quinolones is recommended because these agents effectively penetrate an obstructed biliary tree and can be administered orally. Enterococci and polymicrobial infections are found more commonly in patients with a biliary stent than those without a stent. Pending definitive biliary decompression, patients with sepsis and those who do not quickly respond to treatment with a quinolone may benefit from the addition of antibiotic coverage against gram-positive organisms, targeted against Enterococci.

Community-Acquired Pneumonia

Community-Acquired Pneumonia

Pneumonia in the surgical patient: duration of therapy and does the organism matter?

Pneumonia is a frequent complication in the critically ill surgical or trauma patient. Despite its common occurrence and increased attention recently, many basic issues, such as how long to treat and whether the exact causative organism even matters, remain unanswered. Currently, cessation of treatment is based on clinical response, although some data suggest that both the microbiologic and immunologic response within the lung are also important. A thorough knowledge of the likely causative organisms for both early and late pneumonia should allow safe and efficacious empiric antibiotic selection.

Empiric antibiotic selection criteria for respiratory infections in pediatric practice.

Respiratory infections in children may occur as a consequence of resistant bacterial pathogens. Streptococcus pneumoniae organisms resistant to penicillin, trimethoprim/sulfamethoxazole and macrolides are increasingly prevalent. Amoxicillin- and macrolide-resistant Haemophilus influenzae and Moraxella (Branhamella) catarrhalis are also more commonly seen. Traditional agents such as amoxicillin and trimethoprim/sulfamethoxazole remain acceptable choices for most children with respiratory infections because currently most patients are not infected by resistant pathogens and there is a high spontaneous cure rate associated with these infections. To analyze the criteria for the selection of extended spectrum antimicrobials as empiric therapy for respiratory infections. When an extended spectrum antimicrobial is appropriate for empiric therapy, selection should be based on: (1) efficacy; (2) adverse event profile; and (3) compliance-enhancing features (dosing with meals, once or twice daily administration, good palatability in suspension, shortened course of therapy and affordability). A new agent, ceftibuten, has recently joined other extended spectrum cephalosporins and newer macrolides (clarithromycin and azithromycin) as a choice to be considered for empiric therapy for respiratory infections. These antimicrobials are differentiated from each other and traditional agents by differences in activity in vitro against penicillin-resistant pneumococci, relative beta-lactamase stability against Gram-negative bacteria and pharmacodynamic properties. When resistant organisms are isolated or suspected in community-acquired respiratory infections, cautious use of newer antibiotics may have to be considered.

Improving Empiric Antibiotic Selection Using Computer Decision Support

Physicians frequently need to start antibiotic therapy before the results of bacterial cultures and antibiotic susceptibility tests are available. We developed and evaluated a computerized antibiotic consultant to assist physicians in the selection of appropriate empiric antibiotics. We used a two-stage random-selection study to compare antibiotics suggested by the antibiotic consultant with 482 associated antibiotic susceptibility results and the concurrent antibiotics ordered by physicians. The antibiotics ordered by randomized physicians were then compared between crossover periods of antibiotic consultant use. The antibiotic consultant suggested an antibiotic regimen to which all isolated pathogens were shown to be susceptible for 453 (94%) of 482 culture results, while physicians ordered an antibiotic regimen to which all isolated pathogens were susceptible for 369 culture results (77%) (P < .001). The physicians who prescribed antibiotics to which all pathogens were susceptible did so a mean of 21 hours after the culture specimens were collected. Physicians ordered appropriate antibiotics within 12 hours of the culture collection significantly more often when they had use of the antibiotic consultant than during the period before use (P < .035). Moreover, 88% of the physicians stated they would recommend the program to other physicians, 85% said the program improved their antibiotic selection, and 81% said they felt use of the program improved patient care. Information from computer-based medical records can be used to help improve physicians' selection of empiric antibiotics for infections.

Improving empiric antibiotic selection using computer decision support

Improving empiric antibiotic selection using computer decision support

Empiric Antibiotic Selection by Physicians: Evaluation of Reasoning Strategies

The objectives of the study were to evaluate the appropriateness of empiric antibiotic selection by housestaff treating medical patients with bacteremia. The design was a prospective, observational study at a university-affiliated hospital. Seventy-eight patients with bacteremia were evaluated. A clinical grade of acceptable or not acceptable was assigned to each antibiotic prescription by a consensus panel. The consensus panel found that 34.6% of antibiotic prescriptions were unacceptable (clinical grade). At least one flaw in the chain of reasoning was found in 56.4% of the 78 cases evaluated. Assessment of the clinical setting was correct in 94.9% of the cases; the portal of entry was identified in 91%; adequate knowledge of the bacterial flora at the suspected site of infection was found in 69%; the diagnostic workup was appropriate in 81%, and the correct antibiotic susceptibility patterns were given in 72%. A correct chain of reasoning was more likely to result in an acceptable clinical grade than flawed reasoning (p less than 0.005). However, an appropriate antibiotic selection was made by some physicians despite flawed reasoning, and inappropriate antibiotic selection occurred in a few cases despite fautless reasoning. In 3.8% of cases, unexpected organisms appeared in blood culture. Prescription of broad spectrum antibiotics may then be learned response. If so, educational efforts that emphasize narrow, rather than broad spectrum prescribing may be inadequate to change physician prescribing habits.

Empirical Selection of Antibiotics for Hand Infections

Bacterial cultures and antibiotic sensitivity tests in a series of recent infections of the hand and forearm were analyzed. Staphylococci (58.6 per cent), beta hemolytic streptococci (12.1 per cent), and Escherichia coli (8.3 per cent) were the organisms most frequently isolated. Knowledge of the gram stain property of organism aids considerably in the empirical selection of antibiotics while awaiting positive identification and sensitivity reports. The possibility of encountering gram positive and gram negative organisms together in an acute infection is extremely small. More than 98 per cent of all gram positive organisms were sensitive to lincomycin, chloramphenicol, and methicillin. Empirical selections of antibiotics for unidentified gram negative organisms are less certain, but kanamycin showed statistical superiority (85.6 per cent). Penicillin for gram positive organisms and streptomycin for gram negative organisms had the highest rates of resistance.