Extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae: risk factors for infection and impact of resistance on outcomes

A multidisciplinary approach to antimicrobial stewardship: evolution into the 21st century

In the 21st century, we face the problems of escalating antibiotic resistance, difficult-to-treat infections and slowed new drug development. Healthcare practitioners are increasingly recognising the importance of good antimicrobial stewardship. Various strategies such as formulary management, prior approval, clinical pathways, post-prescribing evaluation and intravenous to oral conversion have been used singly or in combination to improve prescribing and reduce costs. Combining a multifaceted approach with a full-time dedicated multidisciplinary team appears to be capable of yielding satisfactory clinical and economic outcomes and most importantly, sustaining efforts of antimicrobial stewardship. The multidisciplinary approach to antibiotic management should be tailored to fit the individual needs of an institution. More data are needed to document effects on curbing resistance.

Risk factors for extended-spectrum beta-lactamase-producing Enterobacteriaceae in a neonatal intensive care unit

Risk factors for colonization or infection with extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae during an outbreak in a neonatal intensive care unit (NICU) included low gestational age and exposure to third-generation cephalosporins. We also reviewed the existing medical literature regarding the clinical epidemiology of ESBLs in NICUs .

Pathogens resistant to antimicrobial agents: epidemiology, molecular mechanisms, and clinical management

Resistance to antimicrobial drugs is increasing at an alarming rate among both gram-positive and gram-negative bacteria. Traditionally, bacteria resistant to multiple antimicrobial agents have been restricted to the nosocomial environment. A disturbing trend has been the recent emergence and spread of resistant pathogens and resistance traits in nursing homes, the community, as well as in hospitals. This article reviews the epidemiology, molecular mechanisms of resistance, and treatment options for pathogens resistant to antimicrobial drugs.

Epidemiology and clinical features of bloodstream infections caused by AmpC-type-beta-lactamase-producing Klebsiella pneumoniae

Cases of bacteremia caused by AmpC-type-beta-lactamase-producing Klebsiella pneumoniae isolates were retrospectively studied to determine the epidemiologic features and clinical outcomes of bloodstream infections. Among 389 blood isolates recovered from 1998 to 2002, 65 isolates (16.7%) were found to be extended-spectrum beta-lactamase (ESBL) or AmpC beta-lactamase producers. The beta-lactamases from 61 of the 65 isolates were characterized; 28 of 61 isolates produced AmpC-type enzymes (14 isolates each produced DHA-1 and CMY-1-like enzymes), 32 isolates produced TEM or SHV-related ESBLs, and 1 isolate produced a CTX-M-14-like enzyme. To compare the clinical features and outcomes of bloodstream infections caused by AmpC producers with those caused by TEM- or SHV-related ESBL producers, 27 patients infected with isolates producing AmpC-type enzymes (AmpC group) and 25 patients infected with isolates producing TEM- or SHV-related enzymes (ESBL group) were analyzed. There was no significant difference between the AmpC and the ESBL groups in terms of risk factors. When the initial response was assessed at 72 h after antimicrobial therapy, the treatment failure rate for the AmpC group was 51.9% (14 of 27 patients) and the 7- and 30-day mortality rates were 14.8 and 29.6%, respectively, which were similar to those for the ESBL group. When the mortality rate for the patients who received extended-spectrum cephalosporins as definitive treatment was assessed, all four patients in the DHA-1 group and one of three patients in the CMY-1-like group died. In summary, the prevalence of AmpC enzyme-producing K. pneumoniae was high at the Seoul National University Hospital, and the clinical features and outcomes for the patients infected with AmpC-producing organisms were similar to those for the patients infected with TEM- or SHV-related ESBL producers.

Characteristics, epidemiology and clinical importance of emerging strains of Gram-negative bacilli producing extended-spectrum beta-lactamases

Beta-lactam antimicrobial agents represent the most common treatment for bacterial infections and continue to be the leading cause of resistance to beta-lactam antibiotics among Gram-negative bacteria worldwide. The persistent exposure of bacterial strains to a multitude of beta-lactams has induced dynamic and continuous production and mutation of beta-lactamases in these bacteria, expanding their activity even against the newly developed beta-lactam antibiotics. These enzymes are known as extended-spectrum beta-lactamases (ESBLs). The majority of ESBLs are derived from the widespread broad-spectrum beta-lactamases TEM-1 and SHV-1. There are also new families of ESBLs, including the CTX-M and OXA-type enzymes as well as novel unrelated beta-lactamases. In recent years, there has been an increased incidence and prevalence of ESBLs. ESBLs are mainly found in strains of Escherichia coli and Klebsiella pneumoniae but have also been reported in other Enterobacteriaceae strains and Pseudomonas aeruginosa. Infections with ESBL-producing bacterial strains are encountered singly or in outbreaks, especially in critical care units in hospitals, resulting in increasing cost of treatment and prolonged hospital stays. Not only may nursing home patients be an important reservoir of ESBL-containing multiple antibiotic-resistant organisms, but ambulatory patients with chronic conditions may also harbor ESBL-producing organisms.

Evaluation of the current National Committee for Clinical Laboratory Standards guidelines for screening and confirming extended-spectrum beta-lactamase production in isolates of Escherichia coli and Klebsiella species from bacteremic patients

The National Committee for Clinical Laboratory Standards (NCCLS) recommendations for screening and confirming the production of extended-spectrum beta-lactamases (ESBLs) were evaluated in 115 isolates of Escherichia coli and 157 isolates of Klebsiella spp. from Israeli patients with bacteremia. All isolates were screened using cefotaxime, ceftazidime, and cefpodoxime discs. Confirmatory tests using pairs of discs containing ceftazidime, cefotaxime, or cefpodoxime in which clavulanic acid was added to one of the discs in each pair [inhibitor-potentiated disc diffusion test (IPDDT)] and two double-sided E test strips containing ceftazidime or cefotaxime with and without clavulanic acid were performed on all isolates regardless of the results of screening tests. Isolates that tested positive by one or more confirmatory tests were considered ESBL producers. Overall, 69 (25.4%) strains were found to be ESBL producers. The sensitivity of the NCCLS screening criteria ranged between 98.6% for cefotaxime and 92.8% for ceftazidime, and the specificity ranged between 100% for cefotaxime and cefpodoxime and 99.0% for ceftazidime. The sensitivity of the confirmatory tests ranged between 97.1% for the cefotaxime E test and only 75.4% for the ceftazidime IPDDT discs. All 64 isolates that fell in the intermediate and resistant categories for cefotaxime, as well as all 41 in the same categories for ceftazidime and 68 of 69 in these categories for cefpodoxime, were confirmed as ESBL producers. The use of multiple antimicrobial discs for screening isolates and combinations of IPPDT discs is needed to improve the sensitivity of confirmatory testing. It is recommended that isolates falling in the intermediate and resistant categories in disc diffusion testing be reported as ESBL producers. The use of confirmatory tests should be limited to organisms with inhibition zone diameters ranging between the NCCLS recommendations for ESBL screening and the intermediate category breakpoints.

Endemic occurrence of infections by multidrug-resistantEscherichia coliof four unique serotypes in the elderly population of Israel

During a period of four years, multidrug-resistant Escherichia coli of particular serotypes have been isolated from 255 elderly (>65 years) patients from four hospitals in central Israel. 83% of the isolates belonged to one of four predominant serotypes (O153:H31, O101:H-, O2:H42, and O102:H6). All isolates were producers of extended spectrum beta-lactamases and resistant to ciprofloxacin. To our knowledge, the involved serotypes have hitherto not been reported as etiological agents of extraintestinal human infections (MEDLINE). Pulsed-field gel electrophoresis of isolates from one of the most frequent serotypes indicated a clonal relationship between them. Further investigation of these strains and analysis of their virulence factors may help to confine their spread.

Bloodstream Infections Caused by Enterobacter Species: Predictors of 30-Day Mortality Rate and Impact of Broad-Spectrum Cephalosporin Resistance on Outcome

BACKGROUND

Enterobacter species have become increasingly important nosocomial pathogens. However, resistance to cephalosporins often complicates the treatment of Enterobacter infection. This study was conducted to evaluate the predictors of mortality and the impact of cephalosporin resistance on outcome in patients with Enterobacter bacteremia.

METHODS

A total of 183 patients with Enterobacter bacteremia were retrospectively analyzed. Broad-spectrum cephalosporin resistance was defined as in vitro resistance to cefotaxime or ceftazidime. The main outcome measure was the 30-day mortality rate.

RESULTS

Of 183 patients, 86 (47%) had bacteremia caused by broad-spectrum cephalosporin-resistant Enterobacter species, and their infections were classified as resistant. The 30-day mortality rate of patients with resistant infections (the resistant group) was significantly higher than that of patients with susceptible infections (the susceptible group) (33.7% vs. 18.6%; P=.021). When the 30-day mortality rates were compared according to the primary sites of infection and underlying conditions, the 30-day mortality rates of the resistant group were significantly higher than those of the susceptible group, in patients with an unknown primary site of infection, or in patients with septic shock. Multivariate analysis showed that broad-spectrum cephalosporin resistance was one of the independent risk factors associated with 30-day mortality (odds ratio [OR], 3.69; 95% confidence interval [CI], 1.01-13.52; P=.049). Presentation with septic shock and an increasing Acute Physiology and Chronic Health Evaluation II score were also independent risk factors for mortality (OR, 59.91 [95% CI, 14.93-240.15; P<.001] and 1.52 [95% CI, 1.24-1.86; P<.001], respectively).

CONCLUSIONS

Broad-spectrum cephalosporin resistance adversely affects the outcome of patients with Enterobacter bacteremia, especially those with an unknown primary site of infection and those with septic shock.

Clinical outcome of bacteremic spontaneous bacterial peritonitis due to extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae

BACKGROUND

This study was conducted to evaluate the risk factors for infection and clinical outcomes of bacteremic spontaneous bacterial peritonitis (SBP) due to ESBL-producing E. coli and K. pneumoniae, in patients with advanced liver cirrhosis.

METHODS

The ESBL production was determined by NCCLS guidelines and/or double-disk synergy tests, on stored E. coil and K. pneumoniae blood isolates collected between 1998 and 2002. Of the patients with advanced liver cirrhosis, 15 case patients, with SBP due to ESBL-producers, were compared with 30 matched controls, with SBP due to non-ESBL-producers.

RESULTS

There were no significant differences in age, sex, Child-Pugh scores, or APACHE II scores between the two groups. Significant factors associated with infection by ESBL-producing organisms, according to univariate analysis, were: ICU care, indwelling urinary catheter, central venous catheterization, an invasive procedure within the previous 72 hours, and prior use of antibiotics within the previous 30 days. When assessing the clinical response at 72 hours after the initial antimicrobial therapy, the treatment failure rate was significantly higher in the ESBL group (73.3% vs. 16.7%, p<0.001). Also, overall 30-day mortality rates were 60% (9/15) in the ESBL groups and 23.3% (7/30) in the control group (p=0.015).

CONCLUSION

Among patients with advanced liver cirrhosis, bacteremic SBP due to ESBL-producing E. coil and K. pneumoniae was associated with adverse outcomes, and significantly higher mortality.

Results of two worldwide surveys into physician awareness and perceptions of extended-spectrum β-lactamases

An omnibus survey of microbiologists (n = 400) and a survey of participants (n = 49) in the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) programme were conducted to determine the awareness and prevalence of extended-spectrum beta-lactamases (ESBLs), and the regularity and method of screening. Of the omnibus survey participants, 69% screened regularly for ESBLs, compared with 83% of MYSTIC participants. In both surveys, ESBLs were more common in Klebsiella pneumoniae (73% and 79%, respectively) and Escherichia coli (63% and 81%, respectively) than in other bacteria. The surveys demonstrated that awareness of, and testing for, ESBLs is inconsistent.

Effect of parenteral antibiotic administration on establishment of intestinal colonization in mice by Klebsiella pneumoniae strains producing extended-spectrum beta-lactamases

A mouse model was used to test the hypothesis that antibiotics with activity against anaerobes promote overgrowth of extended-spectrum beta-lactamase-producing Klebsiella pneumoniae strains in stool. Subcutaneous clindamycin consistently promoted establishment of high-density colonization, whereas piperacillin-tazobactam, ceftriaxone, and ceftazidime promoted colonization only when a large inoculum and/or more resistant strain was administered.

Epidemiological investigation of bloodstream infections by extended spectrum cephalosporin-resistant Escherichia coli in a Taiwanese teaching hospital

In an epidemiologic and case-control study including 30 case patients over a 3.5-year period in a Taiwanese university hospital, only beta-lactamase inhibitor use and extended-spectrum cephalosporin use were identified as independent risk factors for nosocomial CMY-2-producing Escherichia coli bloodstream infection, and CMY-2 producers were found more prevalent than extended-spectrum beta-lactamase-producing isolates.

"Collateral damage" from cephalosporin or quinolone antibiotic therapy

"Collateral damage" is a term used to refer to ecological adverse effects of antibiotic therapy; namely, the selection of drug-resistant organisms and the unwanted development of colonization or infection with multidrug-resistant organisms. The risk of such damage can be assessed for different antibiotic classes by a variety of epidemiologic studies. Cephalosporin use has been linked to subsequent infection with vancomycin-resistant enterococci, extended-spectrum beta-lactamase-producing Klebsiella pneumoniae, beta-lactam-resistant Acinetobacter species, and Clostridium difficile. Quinolone use has been linked to infection with methicillin-resistant Staphylococcus aureus and with increasing quinolone resistance in gram-negative bacilli, such as Pseudomonas aeruginosa. Neither third-generation cephalosporins nor quinolones appear suitable for sustained use in hospitals as "workhorse" antibiotic therapy.

Late-onset infection and the role of antibiotic prescribing policies

PURPOSE OF REVIEW

Late-onset infection is a significant cause of morbidity and mortality in low-birth-weight and premature infants. Empirical antibiotic treatment is used as infants can deteriorate rapidly without treatment. Current data on the epidemiology of late-onset infection, the types of antibiotics used, duration of antibiotic use, and antibiotic prescribing policies are reviewed.

RECENT FINDINGS

Epidemiological data on late-onset sepsis is dominated by information concerning developed countries; large prospective data collections have been set up in many such countries. Recent data indicate that late-onset sepsis occurs in one-fifth of very-low-birth-weight infants. There are increasing concerns regarding antibiotic resistance. Antibiotic regimens that do not include third-generation cephalosporins produce less resistance. Strategies of antibiotic rotation have not been documented as producing a marked effect on the development of resistant micro-organisms, but there is a lack of randomized trials. Recommendations for preventing the spread of vancomycin-resistant enterococci, produced by the Hospital Infection Control Practices Advisory Committee, have been shown to be effective in a number of situations. Recent reports have documented the success of multidisciplinary, systems-orientated approaches for reducing neonatal nosocomial infection.

SUMMARY

Antibiotic prescribing policies have an important role to play in the treatment of late-onset neonatal infection. There is enough evidence to state that narrow-spectrum antibiotics should be used wherever possible and that potent broad-spectrum antibiotics should be kept in reserve. Ongoing prospective surveillance of infection rates, micro-organisms, resistance and antibiotic use is essential.

Co-carriage rates of vancomycin-resistant Enterococcus and extended-spectrum beta-lactamase-producing bacteria among a cohort of intensive care unit patients: implications for an active surveillance program

OBJECTIVE

To assess the co-colonization rates of extended-spectrum beta-lactamase (ESBL)-producing bacteria and vancomycin-resistant Enterococcus (VRE) obtained on active surveillance cultures.

DESIGN

Prospective cohort study.

SETTING

Medical and surgical intensive care units (ICUs) of a tertiary-care hospital.

PATIENTS

Patients admitted between September 2001 and November 2002 to the medical and surgical ICUs at the University of Maryland Medical System had active surveillance perirectal cultures performed. Samples were concurrently processed for VRE and ESBL-producing bacteria.

RESULTS

Of 1,362 patients who had active surveillance cultures on admission, 136 (10%) were colonized with VRE. Among these, 15 (positive predictive value, 11%) were co-colonized with ESBL. Among the 1,226 who were VRE negative, 1,209 were also ESBL negative (negative predictive value, 99%). Among the 1,362 who had active surveillance cultures on admission, 32 (2%) were colonized with ESBL. Among these, 15 (47%) were co-colonized with VRE. Of the 32 patients colonized with ESBL, 10 (31%) had positive clinical cultures for ESBL on the same hospital admission. For these 10 patients, the surveillance cultures were positive an average of 2.7 days earlier than the clinical cultures.

CONCLUSIONS

Patients who are colonized with VRE can also be co-colonized with other antibiotic-resistant bacteria such as ESBL-producing bacteria. Our study is the first to measure co-colonization rates of VRE and ESBL-producing bacteria. Isolating VRE-colonized patients would isolate 47% of the ESBL-colonized patients without the need for further testing. Hence, active surveillance for VRE should also theoretically diminish the amount of patient-to-patient transmission of ESBL-producing bacteria.

Fluoroquinolones protective against cephalosporin resistance in gram-negative nosocomial pathogens

In a matched case-control study, we studied the effect of prior receipt of fluoroquinolones on isolation of three third-generation cephalosporin-resistant gram-negative nosocomial pathogens. Two hundred eighty-two cases with a third-generation cephalosporin-resistant pathogen (203 with Enterobacter spp., 50 with Pseudomonasaeruginosa, and 29 with Klebsiellapneumoniae) were matched on length of stay to controls in a 1:2 ratio. Case-patients and controls were similar in age (mean 62 years) and sex (54% male). Variables predicting third-generation cephalosporin resistance were surgery (p = 0.005); intensive care unit stay (p < 0.001); and receipt of a β-lactam/β-lactamase inhibitor (p < 0.001), a ureidopenicillin (p = 0.002), or a third-generation cephalosporin (p < 0.001). Receipt of a fluoroquinolone was protective against isolation of a third-generation cephalosporin-resistant pathogen (p = 0.005). Interventional studies are required to determine whether replacing third-generation cephalosporins with fluoroquinolones will be effective in reducing cephalosporin resistance and the effect of such interventions on fluoroquinolone resistance.

Outbreak of extended-spectrum beta-lactamase-producing Klebsiella pneumoniae in a neonatal intensive care unit linked to artificial nails

BACKGROUND

From April to June 2001, an outbreak of extended-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae infections was investigated in our neonatal intensive care unit.

METHODS

Cultures of the gastrointestinal tracts of patients, the hands of healthcare workers (HCWs), and the environment were performed to detect potential reservoirs for ESBL-producing K. pneumoniae. Strains of K. pneumoniae were typed by pulsed-field gel electrophoresis using XbaI. A case-control study was performed to determine risk factors for acquisition of the outbreak clone (clone A); cases were infants infected or colonized with clone A and controls (3 per case) were infants with negative surveillance cultures.

RESULTS

During the study period, 19 case-infants, of whom 13 were detected by surveillance cultures, harbored clone A. The overall attack rate for the outbreak strain was 45%; 9 of 19 infants presented with invasive disease (n = 6) or developed invasive disease (n = 3) after colonization was detected. Clone A was found on the hands of 2 HCWs, 1 of whom wore artificial nails, and on the designated stethoscope of a case-infant. Multiple logistic regression analysis revealed that length of stay per day (odds ratio [OR], 1.05; 95% confidence interval [CI95], 1.02 to 1.09) and exposure to the HCW wearing artificial fingernails (OR, 7.87; CI95, 1.75 to 35.36) were associated with infection or colonization with clone A.

CONCLUSION

Short, well-groomed, natural nails should be mandatory for HCWs with direct patient contact

A study of female urinary tract infection caused by urodynamic investigation

OBJECTIVE

The purpose of this study was to assess the prevalence of female urinary tract infection before and after urodynamic investigation and to identify the risk factors for urinary tract infection after urodynamic investigation.

STUDY DESIGN

Eight hundred twenty-two consecutive incontinent women were recruited. All women were "double-screened" and treated for urinary tract infection before urodynamic investigation: first by mid stream urine culture 4 to 6 weeks before investigation and then by reagent strips for urine leukocytes and nitrites at the time of investigation. The investigation was postponed until the urinary tract infection had been treated. All women then received a standard urodynamic investigation.

RESULTS

The prevalence of urinary tract infection before urodynamic investigation was 5.1% (95% CI, 3.6-6.6), and the prevalence after the investigation was 8.4% (95% CI, 6.5-10.3). Three independent risk factors were identified: age >or=70 years (odds ratio, 1.99; 95% CI, 1.14-3.48), previous continence surgery (odds ratio, 1.90; 95% CI, 1.05-3.43), and urinary tract infection before urodynamic investigation (odds ratio, 3.13; 95% CI, 1.43-6.83). The 3 most common uropathogens in the urinary tract infections after the urodynamic investigation were Escherichia coli (46.3%), Enterococcus spp (16.4%), and Enterococcus faecalis (11.9%).

CONCLUSION

Despite a stringent screen-and-treat protocol before urodynamic investigation, patients still experienced urinary tract infection.

Prevalence of extended spectrum β-lactamase producing escherichia coli and klebsiella isolates in a large community teaching hospital in connecticut

The prevalence of extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli (ESC) and Klebsiella (KS) among consecutive non-urine isolates were evaluated. Twenty-four of 392 isolates produced ESBLs. Among these half were from respiratory sites and all were susceptible to meropenem. Pulse field-gel electrophoresis (PFGE) showed 12 clonally distinct ESBLs and iso-electric focusing (IEF) revealed that most (83%) produced multiple enzymes.

Cephalosporin-resistant Escherichia coli among summer camp attendees with salmonellosis

Investigation of an acute gastroenteritis outbreak involving >100 persons at a summer camp in Girona, Spain, in June 2002 led to the detection of Salmonella and extended-spectrum cephalosporin-resistant Escherichia coli (ESCREC). Stool cultures were performed for 22 symptomatic campers, three asymptomatic food handlers, and 10 healthy household members. Of the 22 campers, 19 had Salmonella enterica, 9 had an ESCREC strain carrying an extended-spectrum β-lactamase, and 2 had a second ESCREC strain carrying a plasmidic cephamycinase. Related ESCREC were detected in two (salmonella-negative) asymptomatic food handlers and in none of the healthy household members. Fecal ESCREC and its β-lactamases and plasmids were extensively characterized. Three of the five ESCREC clones were recovered from multiple hosts. The apparent dissemination of ESCREC suggests a food or water vehicle. The observed distribution of resistance plasmids and β-lactamase genes in several clones indicates a high degree of horizontal transfer. Heightened vigilance and increased efforts must be made to discover the reservoirs and vehicles for community dissemination of ESCREC.

Recent developments in beta lactamases and extended spectrum beta lactamases

Resistance to β lactam antibiotics is an increasing problem worldwide. This review describes the classification and mechanism of action of β lactamases and the options available for detecting, treating, and controlling extended spectrum β lactamases

Appropriate antimicrobial treatment in nosocomial infections—the clinical challenges

Resistance to antimicrobial agents is emerging in a wide variety of pathogens, particularly those that cause nosocomial infections. As a consequence of this increasing resistance, morbidity and mortality in nosocomial infections is also increasing. It is therefore critical to treat nosocomial infections appropriately by starting antimicrobial treatment early in the course of infection, using the correct agent, at the most appropriate dose, and for an adequate duration. Indeed, early 'appropriate' antibiotic prescribing has been shown significantly to reduce mortality, length of intensive care unit and hospital stay and overall costs. Early use of the correct antibiotic at the appropriate dose and for an adequate duration are key to initial appropriate antibiotic prescribing. Choosing the right antibiotic depends mainly on the likely pathogen(s) and the expected local susceptibility patterns. Selection of appropriate antimicrobial therapy requires a thorough understanding of the likely microbial cause of the infection, including local susceptibility patterns, as well as the properties of the antimicrobials available for treating these infections, namely spectrum of activity and potency (including activity versus known resistance mechanisms), pharmacokinetic profile and tolerability and safety. This review, based on a series of presentations at the 5th International Conference of the Hospital Infection Society (Edinburgh, 2002) examines the importance of appropriate antimicrobial therapy in nosocomial infections, and provides guidance on how to achieve this.

Evaluation of VITEK 2 for analysis of Enterobacteriaceae using the Advanced Expert System (AES) versus interpretive susceptibility guidelines used at Dynacare Kasper Medical Laboratories, Edmonton, Alberta

OBJECTIVE

To evaluate the applicability and adaptability of the bioMérieux VITEK 2 Advanced Expert System (AES) to the customized interpretive susceptibility guidelines used at Dynacare Kasper Medical Laboratories (DKML).

METHODS

Three hundred isolates of Enterobacteriaceae (not more than 30% Escherichia coli) were tested on the VITEK 2 system and the API 20E for identification. Susceptibility testing for these isolates was performed on the VITEK 2 system and the Pasco broth microdilution panels. Minimal inhibitory concentrations (MICs) and interpreted results according to the AES and DKML antimicrobial susceptibility guidelines were compared.

RESULTS

Of 300 isolates tested for susceptibility, 13 did not give AES interpretations. Of the remaining 287 isolates, interpretations between AES and DKML guidelines were compared for 10 antibiotics. The overall correlation between the AES and DKML interpretations was 96.2%.

CONCLUSION

This study demonstrated the benefits and limitations of the bioMérieux AES. Automated knowledge-based systems provide a useful laboratory tool for the interpretation of susceptibility results.

Extended-spectrum β-lactamases: implications for the clinical microbiology laboratory, therapy, and infection control

Extended-spectrum beta-lactamase (ESBL) producing gram-negative bacilli are a growing concern in human medicine today. When producing these enzymes, organisms (mostly K. pneumoniae and E. coli) become highly efficient at inactivating the newer third-generation cephaloporins (such as cefotaxime, ceftazidime, and ceftriaxone). In addition, ESBL-producing bacteria are frequently resistant to many classes of non-beta-lactam antibiotics, resulting in difficult-to-treat infections. This review gives an introduction into the topic and is focused on various aspects of ESBLs; it covers the current epidemiology, the problems of ESBL detection and the clinical relevance of infections caused by ESBL-producing organisms. Therapeutic options and potential strategies for dealing with this growing problem are also discussed in this article.

Clinical role of beta-lactam/beta-lactamase inhibitor combinations

The use of beta-lactamase inhibitors in combination with beta-lactam antibiotics is currently the most successful strategy to combat a specific resistance mechanism. Their broad spectrum of activity originates from the ability of respective inhibitors to inactivate a wide range of beta-lactamases produced by Gram-positive, Gram-negative, anaerobic and even acid-fast pathogens. Clinical experience confirms their effectiveness in the empirical treatment of respiratory, intra-abdominal, and skin and soft tissue infections. There is evidence to suggest that they are efficacious in treating patients with neutropenic fever and nosocomial infections, especially in combination with other agents. beta-Lactam/beta-lactamase inhibitor combinations are particularly useful against mixed infections. Their role in treating various multi-resistant pathogens such as Acinetobacter species and Stenotrophomonas maltophilia are gaining importance. Although, generally, they do not constitute reliable therapy against extended-spectrum beta-lactamase producers, their substitution in place of cephalosporins appears to reduce emergence of the latter pathogens. Similarly, their use may also curtail the emergence of other resistant pathogens such as Clostridium difficile and vancomycin-resistant enterococci. beta-Lactam/beta-lactamase inhibitor combinations are generally well tolerated and their oral forms provide effective outpatient therapy against many commonly encountered infections. In certain scenarios, they could even be more cost-effective than conventional combination therapies. With the accumulation of so much clinical experience, their role in the management of infections is now becoming more clearly defined.

Pseudomonas aeruginosa bacteremia: risk factors for mortality and influence of delayed receipt of effective antimicrobial therapy on clinical outcome

Among the nosocomial pathogens, Pseudomonas aeruginosa is recognized as a major cause of morbidity and mortality. Data on 136 patients with P. aeruginosa bacteremia were retrospectively analyzed to evaluate risk factors for mortality. The median age of the patients was 55 years (range, 15-85 years), 78.7% of the cases were hospital-acquired, and the 30-day mortality rate was 39% (53 of 136 patients). Multivariate analysis demonstrated that risk factors for mortality included severe sepsis, pneumonia, delay in starting effective antimicrobial therapy, and an increasing APACHE II score (all P values <.05). In 123 of the 136 patients (excluding 13 patients treated with inadequate definitive antibiotics), 30-day mortality was 27.7% (13 of 47 patients) in the group of patients who received initially effective empirical antimicrobial therapy, and 43.4% (33 of 76) in the group of patients who received delayed effective antimicrobial therapy (P=.079). There was a trend toward higher mortality as the length of delay increased. Delay in starting effective antimicrobial therapy for P. aeruginosa bacteremia tended to be associated with higher mortality.

The influence of infection on hospital mortality for patients requiring > 48 h of intensive care

OBJECTIVE

To determine the influence of microbiologically confirmed infection on hospital mortality among patients requiring intensive care for > 48 h.

DESIGN

Prospective cohort study.

SETTING

Medical ICU of the Barnes-Jewish Hospital, an urban teaching hospital.

PATIENTS

A total of 893 patients requiring intensive care for > 48 h.

INTERVENTIONS

Prospective patient surveillance and data collection.

MEASUREMENTS AND MAIN RESULTS

Three hundred seventy-two patients (41.7%) requiring intensive care for > 48 h had a microbiologically confirmed infection. Only six patients (0.7% [1.6% of patients with microbiologically confirmed infections]) received inadequate antimicrobial therapy during the first 24 h of treatment, and 248 patients (27.8%) died during hospitalization. Compared to hospital survivors, hospital nonsurvivors were significantly more likely to have a microbiologically confirmed infection (53.2% vs 37.2%, respectively; p < 0.001) and to develop severe sepsis (45.6% vs 28.7%, respectively; p < 0.001). Cirrhosis and the requirement for vasopressors were the only variables identified by multiple logistic regression analysis as independent risk factors for hospital mortality in all patient groupings of severity of illness. Multiple logistic regression analysis also demonstrated that underlying malignancy (adjusted odds ratio [AOR], 1.98; 95% CI, 1.55 to 2.53), chronic renal insufficiency (AOR, 1.57; 95% CI, 1.31 to 1.87), cirrhosis (AOR, 1.94; 95% CI, 1.48 to 2.53), temperature > 38.3 degrees C (AOR, 1.72; 95% CI, 1.47 to 2.02), severe sepsis (AOR, 2.78; 95% CI, 1.94 to 3.98), positive culture for vancomycin-resistant enterococci (AOR, 1.78; 95% CI, 1.51 to 2.09), and the presence of multiple infections (AOR, 1.65; 95% CI, 1.28 to 2.14) were independently associated with the requirement for therapy with vasopressors.

CONCLUSIONS

Microbiologically confirmed infections are common among patients requiring medical intensive care for > 48 h. Despite the administration of adequate antimicrobial therapy, microbiologically confirmed infections appear to be an important cause of hemodynamic instability and increased hospital mortality. These data suggest that clinical efforts aimed at the prevention of infections and improvements in the medical management of patients with severe infections, especially those associated with hemodynamic instability and the need for vasopressors, are required to achieve further improvements in patient outcomes.

Extended spectrum beta lactamase-producing Klebsiella pneumoniae infections: a review of the literature

Infections caused by extended-spectrum beta-lactamase (ESBL)-producing pathogens, particularly Klebsiella pneumoniae, are increasing. The epidemiology of ESBL-producing K. pneumoniae, the mechanisms of resistance, and treatment strategies for infections caused by these organisms are reviewed.

Outcome of antibiotic therapy for third-generation cephalosporin-resistant Gram-negative bacteraemia: an analysis of 249 cases caused by Citrobacter, Enterobacter and Serratia species

Two hundred and forty-nine patients with monomicrobial bacteraemia due to third-generation cephalosporin (TGC)-resistant Citrobacter freundii (42), E. aerogenes (23), E. cloacae (143), and Serratia marcescens (41) were analyzed for antibiotic therapy used and outcome. For isolates with resistance to any of the TGCs, all beta-lactams, except imipenem, were considered ineffective. Of 152 patients given appropriate treatment, the mortality rates were 10.9% for 128 patients given monotherapy and 25.0% for 24 patients given combination therapy (P=0.09). Of patients given monotherapy, there were no significant differences in mortality between imipenem, aminoglycoside, and ciprofloxacin treatment groups (P=0.57). Only shock was associated with mortality in multivariate analysis. In conclusion, for patients with TGC-resistant Gram-negative bacteraemia, no significant difference in outcome was observed between single antibiotic therapy groups or monotherapy and combination therapy groups.

The impact of antimicrobial resistance on health and economic outcomes

Despite an increasing prevalence of antimicrobial-resistant pathogens, the health and economic impact of colonization and infection with these organisms has not been fully elucidated. We explore how antimicrobial resistance can affect patient outcomes by enhancing virulence, causing a delay in the administration of appropriate therapy, and limiting available therapy. Next, we examine the different perspectives held by hospitals, third-party payers, patients, and society on the impact of resistance. Finally, we review methodological issues in designing and assessing studies that address the clinical outcomes for patients infected or colonized with resistant pathogens, including adjustment for important confounding variables, control group selection, and the quantification of economic outcomes.

Pharmacokinetics-pharmacodynamics of cefepime and piperacillin-tazobactam against Escherichia coli and Klebsiella pneumoniae strains producing extended-spectrum beta-lactamases: report from the ARREST program

The frequency of resistance to beta-lactams among nosocomial isolates has been increasing due to extended-spectrum beta-lactamase (ESBL)-producing enteric bacilli. Although clinical outcome data are desirable, assessment of clinical efficacy has been limited due to the lack of a statistically meaningful number of well-documented cases. Since time above the MIC (T>MIC) is the pharmacokinetic-pharmacodynamic (PK-PD) measure that best correlates with in vivo activity of beta-lactams, a stochastic model was used to predict the probability of PK-PD target attainment ranging from 30 (P30) to 70% (P70) T>MIC, for standard dosing regimens of both piperacillin-tazobactam and cefepime against Escherichia coli and Klebsiella pneumoniae ESBL phenotypes. The P70/30 T>MIC for cefepime at 2 g every 12 h against E. coli and K. pneumoniae was 0.99/1.0 and 0.96/1.0 and for a regimen of 1 g every 12 h was 0.96/1.0 and 0.93/0.99, respectively. For piperacillin-tazobactam at 3.375 g every 4 h against E. coli and K. pneumoniae, the P70/30 T>MIC was 0.77/0.96 and 0.48/0.77 and for a regimen of 3.375 g every 6 h was 0.28/0.91 and 0.16/0.69, respectively. These data suggest that the probability of achieving T>MIC target attainment rates is generally higher with cefepime than with piperacillin-tazobactam for present-day ESBL-producing strains when one uses contemporary dosing regimens.

Carriage of methicillin-resistant Staphylococcus aureus, ceftazidime-resistant Gram-negative bacilli, and vancomycin-resistant enterococci before and after intensive care unit admission

OBJECTIVE

To measure patients' risk for acquiring antibiotic-resistant microorganisms associated with intensive care unit admission.

DESIGN

Prospective, observational study.

SETTING

Ten public hospitals including one university medical center.

PATIENTS

Consecutive patients admitted to ten intensive care units.

INTERVENTIONS

Serial patient surveillance cultures were screened for vancomycin-resistant enterococci, methicillin-resistant Staphylococcus aureus (MRSA), ceftazidime-resistant Gram-negative bacilli (CR-GNB), Acute Physiology and Chronic Health Evaluation II score, and antibiotic and medical device exposures.

MEASUREMENTS AND MAIN RESULTS

A total of 1,697 patient admissions in ten intensive care units were enrolled. The overall carriage rate of antibiotic-resistant bacteria at intensive care unit entry was 12.1% for MRSA, 14% for CR-GNB and 4.7% for both. At discharge from the intensive care unit, new carriage of MRSA, CR-GNB, and both was found in 11.1%, 14.2%, and 2.4% of the patients, respectively. The acquisition rates in the individual units correlated highly and positively with proportion of patients with carriage at intensive care unit entry for both MRSA (n = 10, Pearson's r =.89, p < 0.001) and CR-GNB (n = 10, Pearson's r =.92, p < 0.001). By logistic regression, severity of illness (odds ratio, 1.4), length of stay (odds ratio, 1.7), use of penicillins (odds ratio, 1.9), and number of antibiotics (odds ratio, 1.2) and medical devices (odds ratio, 1.2) were independently associated with intensive care unit acquisition of MRSA. In comparison, variables independently associated with intensive care unit acquisition of CR-GNB were Acute Physiology and Chronic Health Evaluation II score (odds ratio, 1.5), number of antibiotics (odds ratio, 1.1), and artificial airway (odds ratio, 1.5).

CONCLUSIONS

These data suggest that hospitalization in the intensive care unit introduces significant risk to patients in terms of transmission of MRSA and/or CR-GNB. This risk seems to be influenced strongly by the proportion of patients with colonization at intensive care unit admission and is associated with severity of illness, length of stay, and exposures to antibiotics and medical devices.

Restriction of third-generation cephalosporin use decreases infection-related mortality

OBJECTIVE

To determine the effect of restriction of third-generation cephalosporin use on antibiotic resistance and the outcome of patients with infection.

DESIGN

A prospective, before-after comparative study.

SETTING

A general intensive care unit with 14 beds at a university-affiliated teaching hospital.

PATIENTS

All patients admitted to the intensive care unit within 2 yrs.

INTERVENTIONS

A new antibiotic treatment strategy was implemented during phase II. All patients with confirmed or suspected Gram-negative bacterial infections were treated mainly with antibiotics other than third-generation cephalosporins.

MEASUREMENTS AND MAIN RESULTS

Antibiotic resistance among common Gram-negative bacilli and infection-related hospital mortality during phase I were compared with phase II. A 26.6% reduction in third-generation cephalosporin use (from 168.2 +/- 48.0 to 123.5 +/- 39.3 g/month, p =.021), accompanied by a 277.7% increase in cefepime use (from 10.3 +/- 19.2 to 38.9 +/- 31.7 g/month, p =.014) occurred in phase II compared with phase I. This was accompanied by a significant decrease in reduced susceptibility of Gram-negative bacilli to third-generation cephalosporins (p <.05), mainly because of the improved susceptibility of Escherichia coli and Klebsiella species (p <.05). Infection-related hospital mortality was significantly lower in phase II (19.3% vs. 36.3%, p =.014). Multiple logistic regression analysis demonstrated lower respiratory tract infection, the status of immunocompromise, and continuous veno-venous hemofiltration as independent risk factors for infection-related hospital mortality (p <.05), whereas infection with E. coli or Klebsiella species (p =.039) and restriction of third-generation cephalosporin use (p =.025) were associated with a significantly lower mortality rate.

CONCLUSIONS

Restriction of third-generation cephalosporin use may improve the antibiotic susceptibility and reduce infection-related hospital mortality in critically ill patients.

Changes in the prevalence of vancomycin-resistant enterococci in response to antimicrobial formulary interventions: impact of progressive restrictions on use of vancomycin and third-generation cephalosporins

This study sought to assess the impact of restricting use of vancomycin and third-generation cephalosporins on vancomycin-resistant enterococci (VRE) prevalence. All clinical enterococcal isolates identified at a large academic medical center during a 10-year period were analyzed. Changes in VRE prevalence after sequential restrictions on use of vancomycin and third-generation cephalosporins were evaluated. The correlation between antibiotic use and VRE prevalence was also investigated. Vancomycin use initially decreased by 23.9% but returned to preintervention levels by the end of the study. Third-generation cephalosporin use decreased by 85.8%. However, VRE prevalence increased steadily from 17.4% to 29.6% during the 10-year period (P<.001). Clindamycin use was significantly correlated with VRE prevalence. Restricting the use of vancomycin and third-generations cephalosporins had little impact on VRE prevalence. The association between clindamycin use and the prevalence of VRE suggests that restriction of this and perhaps other antianaerobic agents might be an important component of future antimicrobial interventions.

[Risk factors associated with ceftazidime-resistant Klebsiella pneumoniae infection]

INTRODUCTION

Risk factors associated with ceftazidime-resistant Klebsiella pneumoniae (CAZ-R Kp) infection may vary among hospitals and in the same hospital at different time points. Knowledge of these factors is required to establish suitable infection control programs.

METHODS

A case-control study was conducted to assess risk factors for CAZ-R Kp infection. Thirty-two cases were compared with 28 controls admitted to a 200-bed general hospital during 1999 and 2000.

RESULTS

In the univariate analysis Kp CAZ-R isolates were significantly associated with nosocomial acquisition (OR 5 17.40), prior antibiotic use (OR 5 14.94), particularly ciprofloxacin use (OR 5 5), and hospitalization stay of more than 6 days (OR 5 6.72). Significantly associated variables in the logistic regression analysis included nosocomial acquisition (OR 5 9.29), prior antibiotic use (OR 5 6.21), and particularly, ciprofloxacin use (OR 5 10.84).

CONCLUSIONS

Efforts toward more rational overall antibiotic use and particularly ciprofloxacin use, combined with infection control measures are necessary to decrease the prevalence of CAZ-R Kp in our hospital.

Emergence in Klebsiella pneumoniae of a chromosome-encoded SHV beta-lactamase that compromises the efficacy of imipenem

A Klebsiella pneumoniae isolate was identified that had reduced susceptibility to several expanded-spectrum cephalosporins and imipenem. That isolate produced a chromosome-encoded SHV-type beta-lactamase, SHV-38, that had an alanine to valine substitution in position Ambler 146 compared to beta-lactamase SHV-1. The kinetic parameters for purified beta-lactamases SHV-38 and SHV-1 showed that the hydrolytic spectrum of SHV-38 included only ceftazidime and imipenem. This report is the first example of an SHV-type beta-lactamase capable of hydrolyzing imipenem.

Risk factors in the acquisition of extended-spectrum beta-lactamase Klebsiella pneumoniae: a case-control study in a district teaching hospital in Taiwan

A case-control study was performed to find the risk factors in the acquisition of extended-spectrum beta-lactamase (ESBL) Klebsiella pneumoniae. From 1 May 2001 to 30 September 2001, 422 isolates ofK. pneumoniae identified by the microbiological laboratory in Hsin-Chu hospital were collected, 59 of which were ESBL-producing strains. The prevalence rate was 14% (59/422). There were 43 case patients (ESBL-producing K. pneumoniae) and 86 controls (non-ESBL-producing K. pneumoniae). Tracheostomy, insertion of a Foley catheter, endotracheal tube, nasogastric tube and central venous catheter were found to be risk factors in the acquisition of K. pneumoniae with ESBLs by univariate analysis. Tracheostomy (odds ratio, 5.13; 95% CI, 1.24-21.1;P =0.023) and ceftazidime use (odds ratio, 13.40; 95% CI, 1.21-148.85; P=0.035) remained as risk factors by multivariate analysis with logistic regression. Other anti-pseudomonal agents should be used as empirical therapy to treat possible Pseudomonas aeruginosa infection in order to reduce ceftazidime use and thereby decrease the prevalence of ESBL producing strains of Enterobacteriaceae.

Occurrence and phenotypic characteristics of extended-spectrum beta-lactamases among members of the family Enterobacteriaceae at the Tel-Aviv Medical Center (Israel) and evaluation of diagnostic tests

We assessed the prevalence and phenotypic characteristics of extended-spectrum beta-lactamase (ESBL) producers among cefuroxime-resistant (CXM-R) (MIC > or = 32 micro g/ml) members of the family Enterobacteriaceae in our institution. The 438 CXM-R clinical isolates obtained from nonurine sources among inpatients were screened. ESBL production was confirmed by disk diffusion assay using cefpodoxime (CPD), cefotaxime (CTX), and ceftazidime (CTZ) with and without clavulanate (CLAV). A difference of > or =5 mm in the size of the zone of inhibition in the presence of CLAV for at least one of the agents was considered representative of the ESBL phenotype: 186 isolates (42.5%) were confirmed as ESBL producers. The isolates tested and the rates of ESBL producers were as follows: Klebsiella spp. (n = 81), 79%; Proteus spp. (n = 58), 62%; Escherichia coli (n = 64), 53%; Enterobacter spp. (n = 69), 42%; Serratia spp. (n = 70), 14%; Citrobacter spp. (n = 25), 24%; Providencia spp. (n = 21), 24%; Morganella spp. (n = 41), 5%; and Kluyvera (n = 3), 0%. The overall sensitivity of isolated ESBL confirmatory tests was 79% for CPD-CLAV, 66% for CTZ-CLAV, and 91% for CTX-CLAV. Sensitivities of CTZ-CLAV confirmatory tests for Klebsiella spp., Proteus spp., E. coli, and Enterobacter spp. were 84, 22, 76, and 62%, respectively, and those for CTX-CLAV were 95, 97, 94, and 83%, respectively. They were 90% for CPD-CLAV and CTZ-CLAV, 95% for CPD-CLAV and CTX-CLAV, and 100% for CTZ-CLAV and CTX-CLAV. ESBL production was highly prevalent among Enterobacteriaceae. Using resistance to CXM as an ESBL screening criterion is a suitable option in high-incidence areas where Klebsiella spp. are not the dominant ESBL producers. This screening criterion may simplify the screening test and improve its sensitivity, although at the price of testing more isolates. The CTX-CLAV combination confirmed ESBL producers better than the CTZ-CLAV combination, with sensitivity varying between species. Combined CTZ-CLAV and CTX-CLAV testing detected all these strains; CPD-CLAV provided no additional benefit.

Evaluation of the Etest ESBL and the BD Phoenix, VITEK 1, and VITEK 2 automated instruments for detection of extended-spectrum beta-lactamases in multiresistant Escherichia coli and Klebsiella spp

Seventy-four isolates of multiresistant Escherichia coli and Klebsiella spp. recovered during a 3-year period and 17 control strains with genotypically identified beta-lactamases were tested for the production of extended-spectrum beta-lactamases (ESBLs) by using the Etest and the VITEK 1, VITEK 2, and Phoenix automated instruments. The use of the Etest was evaluated by investigating its accuracy in detecting the ESBLs of the control strains and by comparing interpretation results of laboratory technicians and experts. The accuracy of the Etest was 94%. With the Etest as the reference for the clinical strains and the genotype as the reference for the control strains, the automated instruments detected the ESBLs with accuracies of 78% (VITEK 2), 83% (VITEK 1), and 89% (Phoenix). No significant difference between the systems with regard to the control strains was detected. The VITEK 2 did, however, perform less well than the Phoenix (P = 0.03) on the collection of clinical isolates, mainly because of its high percentage of indeterminate test results (11%). No significant difference between the performances of the VITEK 1 and either the VITEK 2 or the Phoenix was found. However, because of its associated BDXpert system the Phoenix showed the best performance. The Etest was found to be an accurate test but was limited by its indeterminate results (4%), its inability to differentiate between K1 hyperproduction and ESBLs, questionable guidelines concerning mutants inside the inhibition zones, and the inability of the technicians to recognize subtle zone deformations.

Clinical implications of extended-spectrum beta-lactamase-producing Klebsiella pneumoniae bacteraemia

To identify the clinical implications of extended-spectrum beta-lactamase (ESBL) production, 162 cases of Klebsiella pneumoniae bacteraemia in 154 adults were analysed. Of these cases, 44 (27.2%) were ESBL-producing (ESBLKP). Common sources of ESBLKP bacteraemia included primary bacteraemia (34.1%) and biliary infection (29.5%). The placement of a biliary drainage catheter, nosocomial acquisition, and prior antibiotic therapy were independently associated with ESBL production in multivariate analysis. More cases of ESBLKP than non-ESBLKP received inappropriate antibiotic therapy before culture results were reported (54.5 vs. 3.4%; P = 0.001). In 19 cases of ESBLKP, no significant difference in mortality was observed between patients who received appropriate empiric antibiotic therapy and those who did not (26.3 vs. 20.8%; P = 0.67). The mean length of hospital stay after the onset of bacteraemia was longer in the cases of ESBLKP than in the cases of non-ESBLKP (39.6 vs. 23.9 days; P = 0.008). Directly related mortality was not significantly different between the cases of ESBLKP and the cases of non-ESBLKP (23.3 vs. 20.0%; P = 0.65). None of the patients with biliary infection due to ESBLKP died (0/12; P = 0.03). In conclusion, ESBL production was not significantly associated with death but it had a considerable impact on patients with K. pneumoniae bacteraemia.

Hospital-acquired infections in the neonatal intensive care unit--Klebsiella pneumoniae

Klebsiella pneumoniae is medically the most important organism of the Klebsiella species. It is responsible for a significant proportion of hospital-acquired infections including septicemias, urinary tract infections, pneumonia, and soft tissue infections especially in the immunocompromised hosts such as the neonate. The hands of healthcare workers and the gastrointestinal tract of hospitalized infants serve as reservoirs for the transmission of the organism and are responsible for multiple hospital outbreaks. In recent years, there has been an increase in the incidence of outbreaks caused by multidrug resistance K. pneumoniae organisms or the extended spectrum beta-lactamase (ESBL)-producing K. pneumoniae. The problems associated with extended spectrum beta-lactamase-producing organisms include difficulties in accurate antimicrobial susceptibility testing, limited treatment options and increased morbidity and perhaps mortality. Hence, prevention through implementation of strict infection control guidelines, effective hand washing and judicious use of antimicrobials such as third generation cephalosporins is important to effectively reduce the morbidity associated with this infection.

Extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella species: risk factors for colonization and impact of antimicrobial formulary interventions on colonization prevalence

OBJECTIVE

The incidence of extended-spectrum beta-lactamase (ESbetaL)-mediated resistance has increased markedly during the past decade. Risk factors for colonization with ESbetaL-producing Escherichia coli and Klebsiella species (ESbetaL-EK) remain unclear, as do methods to control their further emergence.

DESIGN

Case-control study.

SETTING

Two hospitals within a large academic health system: a 725-bed academic tertiary-care medical center and a 344-bed urban community hospital.

PATIENTS

Thirteen patients with ESbetaL-EK fecal colonization were compared with 46 randomly selected noncolonized controls.

RESULTS

Duration of hospitalization was the only independent risk factor for ESbetaL-EK colonization (odds ratio, 1.11; 95% confidence interval, 1.02 to 1.21). Of note, 8 (62%) of the patients had been admitted from another healthcare facility. In addition, there was evidence for dissemination of a single K oxytoca clone. Finally, the prevalence of ESbetaL-EK colonization decreased from 7.9% to 5.7% following restriction of third-generation cephalosporins (P = .51).

CONCLUSIONS

ESbetaL-EK colonization was associated only with duration of hospitalization and there was no significant reduction following antimicrobial formulary interventions. The evidence for nosocomial spread and the high percentage of patients with ESbetaL-EK admitted from other sites suggest that greater emphasis must be placed on controlling the spread of such organisms within and between institutions.

Extended-Spectrum β-Lactamase Resistance in the ICU

Despite the recent focus on gram-positive infections in the intensive care unit (ICU), gram-negative resistance mechanisms continue to challenge the critical care practitioner. A recent national surveillance study of United States ICUs found Escherichia coli, Enterbacter species, Klebsiella species, and Pseudomonas aeruginosa represented 72% of all gram-negative bacilli recovered. E coli, Klebsiella pneumoniae, and Enterobacter species are significant producers of a β -lactamase that inactivates almost all β -lactam antibiotics, so-called extended-spectrum β -lactamases or ESBLs. Many clinical laboratories may not test for ESBL-production in these organisms, thus clinicians may be unaware of the rising incidence of this plasmid-mediated resistance mechanism. Since initial reports of ESBLs in the 1980s, investigators have found an association with ESBL-producing organisms and the critically ill population. Risk factors for ESBL-related infection in the ICU include arterial, central-venous, and urinary-catheters; mechanical ventilation; abdominal surgery; prior antibiotic therapy with ceftazidime or other extended spectrum cephalosporins; length of time in the ICU; and overall acuity of illness. This article reviews the emergence and epidemiology of the ESBL evolution, describes the clinical implications of ESBL production in the ICU, and outlines a strategy for management of infection in patients at risk for ESBL-producing organisms.

The cost of antibiotic resistance: effect of resistance among Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudmonas aeruginosa on length of hospital stay

To assess the effect of antimicrobial resistance on length of hospital stay, a case-control study compared infections due to four nosocomial pathogens. Significantly increased lengths of stay were associated with infections due to methicillin-resistant Staphylococcus aureus, extended-spectrum beta-lactamase-producing Klebsiella pneumoniae, and carbapenem-resistant Acinetobacter baumannii or Pseudomonas aeruginosa. Infections with resistant pathogens are associated with prolonged hospitalization.