Impact of different methods for describing the extent of prior antibiotic exposure on the association between antibiotic use and antibiotic-resistant infection

Quantifying Gram-Negative Resistance to Empiric Treatment After Repeat ExpoSure To AntimicRobial Therapy (RESTART)

Background

Antibiotic exposure is a primary predictor of subsequent antibiotic resistance; however, development of cross-resistance between antibiotic classes is also observed. The impact of changing to a different antibiotic from that of previous exposure is not established.

Methods

This was a retrospective, single-center cohort study of hospitalized adult patients previously exposed to an antipseudomonal β-lactam (APBL) for at least 48 hours in the 90 days prior to the index infection with a gram-negative bloodstream or respiratory infection. Susceptibility rates to empiric therapy were compared between patients receiving the same (repeat group) versus a different antibiotic from prior exposure (change group).

Results

A total of 197 patients were included (n = 94 [repeat group] and n = 103 [change group]). Pathogen susceptibility to empiric therapy was higher in the repeat group compared to the change group (76.6% vs 60.2%; P = .014). After multivariable logistic regression, repeat APBL was associated with an increased likelihood of pathogen susceptibility (adjusted odds ratio, 2.513; P = .012). In contrast, there was no difference in susceptibility rates between the repeat group and the subgroup of change patients who received an empiric APBL (76.6% vs 78.5%; P = .900). Longer APBL exposure duration (P = .012) and chronic kidney disease (P = .002) were associated with higher nonsusceptibility to the exposure APBL. In-hospital mortality was not significantly different between the repeat and change groups (18.1% vs 23.3%; P = .368).

Conclusions

The common practice of changing to a different APBL from that of recent exposure may not be warranted.

Prediction of ESBL-producing E coli for suspected urinary tract infection

Aim:

The widespread existence of extended-spectrum β-lactamase (ESBL) producing Escherichia coli ( E. coli) has become a critical threat in developed countries. Prediction rule for ESBL producing E. coli is relevant to see patients with suspected urinary tract infection.

Materials and methods:

We collected clinical and laboratory data and constructed multivariate logistic regression models to develop a clinical prediction rule in the derivation cohort with 1185 patients with urine cultures and validated the rule in the validation cohort with 516 patients.

Results:

ESBL-producing E. coli was found in 185 patients (16%) in the derivation cohort. When assigning 14 points for being female (odds ratio (OR): 4.2), six points for CRP >5 mg/dl (OR: 1.87), and four points for a history of urinary tract infection (OR: 1.52), the area under the curve (AUC) had 0.67 (95% confidence interval (CI): 0.63–0.70) in the derivation cohort and 0.64 (95% CI: 0.59–0.69] in the validation cohort.

Conclusions:

The developed prediction rule had moderate accuracy to predict ESBL-producing E. coli in patients with suspected urinary tract infection.

Impact of antibiotic usage on extended-spectrum β-lactamase producing Escherichia coli prevalence

An increase in antibiotic usage is considered to contribute to the emergence of antimicrobial resistance. Although experts are counting on the antimicrobial stewardship programs to reduce antibiotic usage, their effect remains uncertain. In this study, we aimed to evaluate the impact of antibiotic usage and forecast the prevalence of hospital-acquired extended spectrum β-lactamase (ESBL)—producing Escherichia coli (E. coli) using time-series analysis. Antimicrobial culture information of E. coli was obtained using a text processing technique that helped extract free-text electronic health records from standardized data. The antimicrobial use density (AUD) of antibiotics of interest was used to estimate the quarterly antibiotic usage. Transfer function model was applied to forecast relationship between antibiotic usage and ESBL-producing E. coli. Of the 1938 hospital-acquired isolates, 831 isolates (42.9%) were ESBL-producing E. coli. Both the proportion of ESBL-producing E. coli and AUD increased over time. The transfer model predicted that ciprofloxacin AUD is related to the proportion of ESBL-producing E. coli two quarters later. In conclusion, excessive use of antibiotics was shown to affect the prevalence of resistant organisms in the future. Therefore, the control of antibiotics with antimicrobial stewardship programs should be considered to restrict antimicrobial resistance.

Prior Antibiotic Therapy and the Onset of Healthcare-Associated Infections Sustained by Multidrug-Resistant Klebsiella pneumoniae in Intensive Care Unit Patients: A Nested Case-Control Study

Epidemiological research has demonstrated direct relationships between antibiotic consumption and the emergence of multidrug-resistant (MDR) bacteria. In this nested case-control study, we assessed whether prior exposure to antibiotic therapy and its duration affect the onset of healthcare-associated infections (HAIs) sustained by MDR Klebsiella pneumoniae (MDR-Kp) in intensive care unit patients. Cases were defined as patients who developed an MDR-Kp HAI. Controls matched on sex and the length of intensive care unit (ICU) stay were randomly selected from the at-risk population. Any antibiotic agent received in systemic administration before the onset of infection was considered as antibiotic exposure. Multivariable conditional logistic regression analyses were performed to estimate the effect of prior exposure to each antibiotic class (Model 1) or its duration (Model 2) on the onset of HAIs sustained by MDR-Kp. Overall, 87 cases and 261 gender-matched controls were compared. In Model 1, aminoglycosides and linezolid independently increased the likelihood of developing an MDR-Kp HAI, whereas exposure to both linezolid and penicillins reduced the effect of linezolid alone. In Model 2, cumulative exposure to aminoglycosides increased the likelihood of the outcome, as well as cumulative exposures to penicillins and colistin, while a previous exposure to both penicillins and colistin reduced the influence of the two antibiotic classes alone. Our study confirms that aminoglycosides, penicillins, linezolid, and colistin may play a role in favoring the infections sustained by MDR-Kp. However, several double exposures in the time window before HAI onset seemed to hinder the selective pressure exerted by individual agents.

The Association Between the Frequency of Interruptions in Antibiotic Exposure and the Risk of Health Care-Associated Clostridiodes difficile Infection

Background

Although antibiotic use is an established risk factor for health care-associated Clostridiodes difficile infection, estimates of the association between infection and antibiotic use vary, depending upon how antibiotic exposure is measured.

Objectives

The purpose of this study was to explore the association between the frequency of interruptions in antibiotic exposure and the risk of health care-associated C difficile infection.

Methods

A retrospective chart review cohort study was conducted of all inpatients between 2011and 2016 from a single academic health center who received at least 1 dose of a systemic antibacterial for a cumulative duration of >3 days and ≤30 days. The measures of antibiotic exposure examined were duration—cumulative total calendar days of antibiotics therapy—and continuity—the frequency of interruptions in antibiotic exposure that was defined as the number of antibiotic treatment courses.

Results

A total of 52,445/227,967 (23%) patients received antibacterial therapy for >3 days and ≤30 days during their hospitalization. Of these, 1161 out of 52,445 (2.21%) were patients with health care-associated C difficile infection. An adjusted multivariable logistic regression analysis revealed that the risk of C difficile increased with longer cumulative days (odds ratio = 2.7; comparison of >12 days to ≤5 days) and fewer interruptions of antibiotic treatment (odds ratio = 0.78; comparison of >3 discrete antibiotic treatment courses to 1 course or continuous antibiotic treatment course; all P values < 0.05).

Conclusions

For patients who received the same number of cumulative days of therapy, the patients who had more frequently interrupted courses of antibiotic therapy were less likely to experience health care-associated C difficile infection. (Curr Ther Res Clin Exp. 2020; 81:XXX–XXX)

Estimating the association between antibiotic exposure and colonization with extended-spectrum β-lactamase-producing Gram-negative bacteria using machine learning methods: a multicentre, prospective cohort study

OBJECTIVES

The aim of the study was to measure the impact of antibiotic exposure on the acquisition of colonization with extended-spectrum β-lactamase-producing Gram-negative bacteria (ESBL-GNB) accounting for individual- and group-level confounding using machine-learning methods.

METHODS

Patients hospitalized between September 2010 and June 2013 at six medical and six surgical wards in Italy, Serbia and Romania were screened for ESBL-GNB at hospital admission, discharge, antibiotic start, and after 3, 7, 15 and 30 days. Primary outcomes were the incidence rate and predictive factors of new ESBL-GNB colonization. Random forest algorithm was used to rank antibiotics according to the risk of selection of ESBL-GNB colonization in patients not colonized before starting antibiotics.

RESULTS

We screened 10 034 patients collecting 28 322 rectal swab samples. New ESBL-GNB colonization incidence with and without antibiotic treatment was 22/1000 and 9/1000 exposure-days, respectively. In the adjusted regression analyses, antibiotic exposure (hazard ratio (HR) 2.38; 95% CI 1.29-4.40), age 60-69 years (HR 1.19; 95% CI 1.05-1.34), and spring season (HR 1.25; 95% CI 1.14-1.38) were independently associated with new colonization. Monotherapy ranked higher als combination therapy in promoting ESBL-GNB colonization. Among monotherapy, cephalosporins ranked first followed by tetracycline (second), macrolide (fourth) and cotrimoxazole (seventh). Overall the ranking of cephalosporins was lower when used in combination. Among combinations not including cephalosporins, quinolones plus carbapenems ranked highest (eighth). Among sequential therapies, quinolones ranked highest (tenth) when prescribed within 30 days of therapy with cephalosporins.

CONCLUSIONS

Impact of antibiotics on selecting ESBL-GNB at intestinal level varies if used in monotherapy or combination and according to previous antibiotic exposure. These finding should be explored in future clinical trials on antibiotic stewardship interventions.

CLINICAL TRIAL REGISTRATION

NCT01208519.

[Epidemiology of febrile neutropenia in patients with hematological disease-a prospective multicentre survey in China]

OBJECTIVE

To investigate the incidence, clinical and microbiological features of febrile, and risk factors during neutropenia periods in patients with hematological diseases.

METHODS

From October 20, 2014 to March 20, 2015, consecutive patients who had hematological diseases and developed neutropenia during hospitalization were enrolled in the prospective, multicenter and observational study.

RESULTS

A total of 784 episodes of febrile occurred in 1 139 neutropenic patients with hematological diseases. The cumulative incidence of febrile was 81.9% at 21 days after neutropenia. Multivariate analysis suggested that central venous catheterization (P<0.001, HR=3.407, 95% CI 2.276-4.496), gastrointestinal mucositis (P<0.001, HR=10.548, 95% CI 3.245-28.576), previous exposure to broad-spectrum antibiotics within 90 days (P<0.001, HR=3.582, 95% CI 2.387-5.770) and duration of neutropenia >7 days (P<0.001,HR=4.194, 95% CI 2.572-5.618) were correlated with higher incidence of febrile during neutropenia. With the increase of the risk factors, the incidence of febrile increased gradually (35.4%, 69.2%, 86.1%, 95.6%, P<0.001). Of 784 febrile cases, 253 (32.3%) were unknown origin, 429 (54.7% )of clinical documented infections and 102(13.0%) of microbiological documented infections. The most common sites of infection were pulmonary (49.5%), upper respiratory (16.0%), crissum (9.8%), blood stream (7.7%). The most common pathogens were gram-negative bacteria (44.54%), followed by gram-positive bacteria (37.99% ) and fungi (17.47% ). There was no significant difference in mortality rates between cases with febrile and cases without febrile (9.2% vs 4.8%, P=0.099). Multivariate analysis also suggested that >40 years old (P=0.047, HR=5.000, 95% CI 0.853-28.013), hemodynamic instability (P=0.001, HR=13.185, 95% CI 2.983-54.915), prior colonization or infection by resistant pathogens (P=0.005, HR=28.734, 95% CI 2.921-313.744), blood stream infection (P=0.038, HR=9.715, 95% CI 1.110-81.969) and pulmonary infection (P=0.031, HR=25.905, 95% CI 1.381-507.006) were correlated with higher mortality rate in cases with febrile.

CONCLUSIONS

Febrile was the common complication during neutropenia periods in patients with hematological disease. There was different distribution of organisms in different sites of infection. Moreove, the duration of neutropenia >7 days, central venous catheterization, gastrointestinal mucositis and previous exposure to broad-spectrum antibiotics within 90 days were the risk factors for the higher incidence of febrile.

Ertapenem-Resistant Enterobacteriaceae Risk Factors for Acquisition and Outcomes

Background and Objective.

Carbapenem resistance among Enterobacteriaceae is of concern because of increasing prevalence and limited therapeutic options. Limited research has been focused on understanding ertapenem resistance as a more sensitive marker for resistance to other carbapenems. We sought to determine risk factors for acquisition of ertapenem-resistant, meropenem-susceptible, or intermediate Enterobacteriaceae and to assess associated patient outcomes.

Design.

Retrospective case-control study among adult hospitalized inpatients.

Setting.

A 902-bed quaternary care urban hospital.

Results.

Sixty-two cases of ertapenem-resistant Enterobacteriaceae were identified from March 14, 2006, through October 31, 2007, and 62 unmatched control patients were randomly selected from other inpatients with cultures positive for ertapenem-susceptible Enterobacteriaceae. Thirty-seven (60%) of case patient isolates were Enterobacter cloacae, 20 (32%) were Klebsiella pneumoniae, and 5 (8%) were other species of Enterobacteriaceae. Risk factors for ertapenem-resistant Enterobacteriaceae infection included intensive care unit stay (odds ratio [OR], 4.6 [95% confidence interval {CI}, 2.0–10.3]), vancomycin-resistant Enterococcus colonization (OR, 7.1 [95% CI, 2.4–21.4]), prior central venous catheter use (OR, 10.0 [95% CI, 3.0–33.1]), prior receipt of mechanical ventilation (OR, 5.8 [95% CI, 2.1–16.2]), exposure to any antibiotic during the 30 days prior to a positive culture result (OR, 18.5 [95% CI, 4.9–69.9]), use of a β-lactam during the 30 days prior to a positive culture result (OR, 6.9 [95% CI, 3.0–16.0], and use of a carbapenem during the 30 days prior to a positive culture result (OR, 18.2 [95% CI, 2.6–130.0]). For the 62 case patients, 30-day outcomes from the time of positive culture result were 24 discharges (39%), 10 deaths (16%), and 28 continued hospitalizations (44%). The final end point of the hospitalization was discharge for 44 patients (71%) and death for 18 patients (29%).

Conclusions.

Ertapenem-resistant Enterobacteriaceae are important nosocomial pathogens. Multiple mechanisms of resistance maybe in operation. Additional study of ertapenem resistance is needed.

European guidelines for empirical antibacterial therapy for febrile neutropenic patients in the era of growing resistance: summary of the 2011 4th European Conference on Infections in Leukemia

Owing to increasing resistance and the limited arsenal of new antibiotics, especially against Gram-negative pathogens, carefully designed antibiotic regimens are obligatory for febrile neutropenic patients, along with effective infection control. The Expert Group of the 4(th) European Conference on Infections in Leukemia has developed guidelines for initial empirical therapy in febrile neutropenic patients, based on: i) the local resistance epidemiology; and ii) the patient's risk factors for resistant bacteria and for a complicated clinical course. An 'escalation' approach, avoiding empirical carbapenems and combinations, should be employed in patients without particular risk factors. A 'de-escalation' approach, with initial broad-spectrum antibiotics or combinations, should be used only in those patients with: i) known prior colonization or infection with resistant pathogens; or ii) complicated presentation; or iii) in centers where resistant pathogens are prevalent at the onset of febrile neutropenia. In the latter case, infection control and antibiotic stewardship also need urgent review. Modification of the initial regimen at 72-96 h should be based on the patient's clinical course and the microbiological results. Discontinuation of antibiotics after 72 h or later should be considered in neutropenic patients with fever of unknown origin who are hemodynamically stable since presentation and afebrile for at least 48 h, irrespective of neutrophil count and expected duration of neutropenia. This strategy aims to minimize the collateral damage associated with antibiotic overuse, and the further selection of resistance.

Risk factors for colonization with ampicillin and high-level aminoglycoside-resistant enterococci during hospitalization in the ICU and the impact of prior antimicrobial exposure definition: a prospective cohort study

The aim of our prospective cohort study was to determine the incidence, genetic relatedness and risk factors for colonization with ampicillin and high-level aminoglycoside-resistant enterococci (ARHLARE) among patients hospitalized in the intensive care unit. During 15-month period, we included 105 patients. The only independent risk factor for ARHLARE colonization was days of cefotaxime/ceftriaxone therapy [odds ratio (OR): 1.13; 95% confidence interval (CI) 1.10-1.27; P  =  0.045]. Patients with higher total use of antibiotics, patients on prolonged mechanical ventilation, and patients with urinary tract infection (UTI), were also found to be at increased risk to become colonized with ARHLARE. Pulsed-field gel electrophoresis suggested multifocal origin of the majority of the colonizing strains. Our results show that an increase in total antibiotic consumption for 10 defined daily doses (DDD)/patient increased the odds of colonization with ARHLARE for 36%. Further efforts to optimize antimicrobial use in high risk patients are proposed.

Impact of antibiotic use during hospitalization on the development of gastrointestinal colonization with Escherichia coli with reduced fluoroquinolone susceptibility

OBJECTIVE

Infections due to fluoroquinolone-resistant Escherichia coli (FQREC) are associated with significant morbidity and mortality. Fluoroquinolone resistance likely arises at the level of gastrointestinal colonization. The objective of this study was to identify risk factors for the development of FQREC gastrointestinal tract colonization in hospitalized patients, including the impact of antibiotics prescribed during hospitalization.

DESIGN

A prospective cohort study was conducted from 2002 to 2004 within a university health system.

METHODS

Hospitalized patients initially colonized with fluoroquinolone-susceptible E. coli were followed up with serial fecal sampling for new FQREC colonization or until hospital discharge or death. A Cox proportional hazards regression model was developed to identify risk factors for new FQREC colonization, with antibiotic exposure modeled as time-varying covariates.

RESULTS

Of 395 subjects, 73 (18.5%) became newly colonized with FQREC. Length of stay before sampling (hazard ratio [HR], 1.02 [95% confidence interval (CI), 1.1-1.03]; P = .003) and malignancy (HR, 0.37 [95% CI, 0.21-0.67]; P = .001) were significantly associated with the development of FQREC colonization. In addition, receipt of a first-generation cephalosporin (HR, 1.19 [95% CI, 1.10-1.29]; P < .001) or cefepime (HR, 1.05 [95% CI, 1.00-1.10]; P = .048) during hospitalization increased the risk of new FQREC colonization.

CONCLUSIONS

The acquisition of FQREC in the hospital setting is complex, and antimicrobial stewardship programs should take into account patterns of antibiotic use in implementing strategies to reduce the development of new FQREC colonization. Future studies are needed to identify risk factors for infection in hospitalized patients newly colonized with FQREC.

Epidemiological interpretation of studies examining the effect of antibiotic usage on resistance

Bacterial resistance to antibiotics is a growing clinical problem and public health threat. Antibiotic use is a known risk factor for the emergence of antibiotic resistance, but demonstrating the causal link between antibiotic use and resistance is challenging. This review describes different study designs for assessing the association between antibiotic use and resistance and discusses strengths and limitations of each. Approaches to measuring antibiotic use and antibiotic resistance are presented. Important methodological issues such as confounding, establishing temporality, and control group selection are examined.

Escherichia coli and Klebsiella pneumoniae bacteremia in patients with neutropenic fever: factors associated with extended-spectrum β-lactamase production and its impact on outcome

Escherichia coli and Klebsiella pneumoniae are main pathogens in neutropenic fever even if the proportion of Gram-positive cocci is increasing. Extended-spectrum β-lactamases (ESBL)-producing organisms are an emerging problem in nosocomial infection. Nevertheless, until now, information about risk factors for the acquisition and clinical outcomes of bacteremia due to ESBL-producing organisms is limited in neutropenic patients. From medical records collected between January 2007 and December 2008, we identified a total of 101 consecutive patients who developed bacteremia due to E. coli (n = 87) or K. pneumoniae (n = 14). Twenty-six (26 %) cases of bacteremia were caused by ESBL-producing organisms. A hospital stay of >2 weeks during the 3 months preceding bacteremia [adjusted odds ratio (OR), 5.887; 95 % confidence interval (CI), 1.572-22.041] and the use of broad-spectrum cephalosporins in the 4 weeks prior to bacteremia (adjusted OR, 6.186; 95 % CI, 1.616-23.683) were significantly related to the acquisition of ESBL. Twenty-four (92 %) of the ESBL-producing organisms were susceptible to either piperacillin-tazobactam or amikacin. Aminoglycosides (amikacin or isepamicin) were the main appropriate antimicrobial agents used against the ESBL-producing isolates during the initial empirical treatment (16/22, 73 %). However, the 30-day mortality rates for ESBL bacteremia and non-ESBL bacteremia were not significantly different (15 vs 5 %; p = 0.199). As alternatives to carbapenem, piperacillin-tazobactam plus amikacin or isepamicin combinations may be effective empirical therapeutic options for patients with neutropenic fever who are at high risk of developing bacteremia with ESBL-producing pathogens.

Nosocomial acquisition of methicillin-resistant Staphyloccocus aureus (MRSA) and extended-spectrum beta-lactamase (ESBL) Enterobacteriaceae in hospitalised patients: a prospective multicenter study

Background

The risk of acquisition of antibiotic resistant-bacteria during or shortly after antibiotic therapy is still unclear and it is often confounded by scarce data on antibiotic usage.

Primary objective of the study is to compare rates of acquisition of methicillin-resistant Staphylococcus aureus and extended spectrum beta-lactamase-producing Enterobacteriaceae in hospitalised patients, after starting antibiotic therapy.

Methods/Design

The study, running in three European hospitals, is a multicenter, prospective, longitudinal, observational cohort study funded from the European Community's Seventh Framework Programme [FP7/2007-2013] within the project 'Impact of Specific Antibiotic Therapies on the prevalence of hUman host ResistaNt bacteria' (acronym SATURN). Nasal and rectal screening for methicillin-resistant Staphylococcus aureus and extended spectrum beta-lactamase-producing Enterobacteriaceae will be obtained at hospital admission, discharge, at antibiotic start (t₀, within one hour) and at the following intervals: day 3 (t₁), 7 (t₂), 15 (t₃), and 30 (t₄). Two nested case-control studies will be performed. The objective of the first study will be to define individual level of risk related to specific antibiotics. Patients acquiring methicillin-resistant Staphylococcus aureus and extended spectrum beta-lactamase-producing Enterobacteriaceae (cases) will be compared with patients not acquiring antibiotic-resistant strains after starting antibiotic therapy (controls; ratio 1:4). To define the impact of antibiotics on new acquisition of target antibiotic-resistant bacteria, a second nested case-control study will be done (ratio 1:4). Control group will be selected among patients not receiving antibiotics, admitted in the same ward on the day of the corresponding case, with negative cultures at admission. Epidemiological, clinical and microbiological data will be prospective collected.

Discussion

The rationale of this study is to better understand the impact of antibiotic use on acquisition, selection and transmission of antimicrobial resistant-bacteria in European hospitals.

Trial registration

ClinicalTrials.gov NCT01208519.

Variability of intestinal colonization with third-generation cephalosporin-resistant Enterobacteriaceae and antibiotic use in intensive care units

OBJECTIVES

Healthcare-associated infections due to third-generation cephalosporin-resistant Enterobacteriaceae (CRE) have become a major public health threat, especially in intensive care units (ICUs). We assessed and compared β-lactam use, the prevalence of colonization with CRE at admission and the incidence of CRE acquisition across ICUs.

PATIENTS AND METHODS

A cohort study was conducted in 10 ICUs of the Paris (France) metropolitan area between November 2005 and February 2006. Antibiotic use was recorded prospectively in all patients admitted during the study period. Rectal swabs were collected at admission, twice weekly thereafter, before β-lactam prescription and before discharge.

RESULTS

A total of 893 patients provided 3453 rectal swabs; 793 of the patients were newly admitted, mostly for medical reasons (80.7%). On admission, 74 patients (9.6%) were colonized with CRE, including 32 with an extended-spectrum β-lactamase (ESBL)-producing strain. Among the remaining 694 naive patients, 94 acquired CRE during their follow-up, including 31 with an ESBL-producing strain. Incidence rates of colonization ranged from 8.8 to 21.0/1000 patient-days for all CRE, and from 1.4 to 10.9/1000 patient-days for ESBL producers. A majority of patients (68.3%) were prescribed β-lactams during their ICU stay, with defined daily doses ranging from 428 to 985/1000 patient-days. Across ICUs, prescriptions of all antibiotics, β-lactams and carbapenems were significantly correlated to incidence rates of colonization with ESBL-producing CRE.

CONCLUSIONS

The standardized and systematic follow-up of patients in 10 ICUs revealed great heterogeneity in the rates of colonization with ESBL- and non-ESBL-producing CRE, as well as in antimicrobial prescription practices.

Antibiotic use and the risk of carbapenem-resistant extended-spectrum-{beta}-lactamase-producing Klebsiella pneumoniae infection in hospitalized patients: results of a double case-control study

OBJECTIVES

To identify the roles of various antibiotics as risk factors for carbapenem-resistant extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae (KP) infection (ESBL-KP infection).

METHODS

Data were collected over 26 months in a tertiary care university hospital with established endemicity of carbapenem-resistant ESBL-KP (ESBL-CRKP). Using a case-case-control design, patients who presented an infection caused by carbapenem-susceptible ESBL-KP (ESBL-CSKP) and patients with ESBL-CRKP infection were compared with a common control group of hospitalized patients. Effects of treatment and duration of treatment with antibiotics were examined, adjusting for major non-antibiotic risk factors and controlling for confounding effects among the antibiotics via logistic regression models.

RESULTS

Ninety-six ESBL-CRKP cases, 55 ESBL-CSKP cases and 151 controls were analysed. Multivariate analysis, adjusting for major non-antibiotic risk factors, showed that the risk of ESBL-CRKP infection rose with increasing duration of prior treatment with β-lactam/β-lactamase inhibitor combinations [odds ratio (OR) 1.15 per day increase; P = 0.001] and revealed that increased duration of treatment with fluoroquinolones amplified the impact of exposure to carbapenems (and vice versa) on ESBL-CRKP infection risk (OR 1.02 for interaction term; P = 0.009). Duration of prior treatment with fluoroquinolones was also associated with increased risk of ESBL-CSKP infection (OR 1.07 per day increase; P = 0.028), while prior receipt of carbapenems presented a protective effect against ESBL-CSKP infection (OR 0.21; P = 0.003).

CONCLUSIONS

This study highlights the major role of treatment and duration of treatment with β-lactam/β-lactamase inhibitor combinations and combinations of carbapenems with fluoroquinolones. Clinicians should counterweight the potential benefits of administering these antibiotics against the increased risk of ESBL-CRKP infection.

Antimicrobial use: risk driver of multidrug resistant microorganisms in healthcare settings

PURPOSE OF REVIEW

This review explores recent evidence on the association between antibiotics usage and resistance.

RECENT FINDINGS

A meta-analysis showed that the risk of acquiring methicillin-resistant Staphylococcus aureus was increased by 1.8-fold in patients who had taken antibiotics. Such risk was almost three-times greater after using quinolones or glycopeptides. Significant heterogeneity between studies was mainly related to study designs. A Cochrane systematic review suggested that, although the quality of the evidence was poor, interventions to improve hospital antibiotic prescribing were associated with a reduction in the incidence of antimicrobial resistant pathogens. Against this evidence, mupirocin-resistant S. aureus and linezolid-resistant vancomycin-resistant enterococci (VRE) were detected in institutions where these drugs were not widely used. Studies assessing the impact of vancomycin prescribing restriction on VRE rates were heterogeneous and the effectiveness of such interventions remains poorly defined. Important confounders of studies, other than study design, are the lack of analysis of secular trends of infections, colonization pressure in the ward and duration of follow up.

SUMMARY

Available evidence, although not always of high quality, suggests that a link between antibiotics usage at individual and institutional levels and resistant bacteria does exist. Benchmark guidelines for empiric therapy in hospitalized patients, taking into consideration not only patients' needs but also ecological costs of resistance, should be rapidly developed.

Identifying risk factors for infections: the role of meta-analyses

Systematic review and meta-analysis are assuming greater importance in influencing policy makers and clinical opinion worldwide. Many discussions and publications have considered the merits of meta-analysis of epidemiologic data.50 Some observers suggest that meta-analysis of observational studies should be abandoned altogether. 51 In the authors' opinion, statistical combination of observational studies should not be a primary goal of a review. Analysis of heterogeneity between longitudinal studies, however, would provide more insights than mathematical calculation of the summary risk. Meta-analyses of risk factors for infections should strictly follow guidelines for meta-analyses of observational studies. A study protocol should be written in advance, completed literature searches performed, and studies selected in a reproducible and objective fashion. Biologic plausibility must be addressed. The reported findings should be interpreted with caution, taking into account the limitations of various methodologic aspects of risk factors studies. An important role for meta-analyses in this field would be to clarify hypotheses to be formulated for future Identifying Risk Factors for Infections 221 studies and stress limitations strictly related to studies on risk factors for bacterial and viral infections.

Use of different thresholds of prior antimicrobial use in defining exposure: impact on the association between antimicrobial use and antimicrobial resistance

OBJECTIVES

Although many studies have explored the association between antimicrobial use and antimicrobial resistance, definitions of "exposure" (i.e., prior antimicrobial use) differ across such studies. Specifically, it has been noted that some studies define "exposure" as any antimicrobial use, while others require the administration of at least 24 or 48 h of an antimicrobial to constitute "exposure." The impact of different definitions of exposure on final study results is unknown. We conducted the current study to determine the impact of varying the minimum threshold of prior antimicrobial use to define exposure status in studies of antimicrobial resistance.

METHODS

We used a dataset from a prior study of risk factors for fluoroquinolone (FQ) resistant Pseudomonas aeruginosa (FQRPA) to address the study aim. Four separate multivariable models of risk factors for FQRPA were built. Each model defined a different threshold for the duration of antimicrobial administration to determine "exposure" to that antimicrobial: (1) no threshold (i.e., a subject is considered exposed if any use of the antimicrobial was documented); (2) >24 h of use of the antimicrobial is necessary to be considered exposed; (3) >48 h of use is required; and (4) >72 h of use is required. Except for these definitions, the four multivariable models were built in exactly the same way, each using prior FQ use as the primary risk factor of interest.

RESULTS

Among 872 P. aeruginosa isolates included in the original dataset, 332 (38.2%) were FQ-resistant. Each of the four multivariable models identified prior FQ use as an independent risk factor for FQRPA. However, as increasingly strict thresholds were used, the association between FQ use and FQRPA increased. Furthermore, prior use of an agent with activity against anaerobic bacteria was associated with FQRPA in models 2, 3 and 4, but not in model 1.

CONCLUSIONS

The use of different thresholds to define prior "exposure" to antimicrobials altered the associations between antimicrobial use and resistance. Stricter thresholds resulted in a higher estimate of the association between antimicrobial use and resistance. Furthermore, different risk factors may be identified depending on how exposure is defined. Greater attention to this issue is necessary to optimize identification of modifiable risk factors for resistance as well as accurately compare results across studies.