Antimicrobial Stewardship Opportunities in Critically Ill Patients with Gram-Negative Lower Respiratory Tract Infections: A Multicenter Cross-Sectional Analysis

INTRODUCTION

Lower respiratory tract infections (LRTIs) are a major cause of morbidity and death. Because of changes in how LRTIs are defined coupled with the increasing prevalence of drug resistance, there is a gap in knowledge regarding the current burden of antimicrobial use for Centers for Disease Control and Prevention (CDC)-defined LRTIs. We describe the infection characteristics, antibiotic consumption, and clinical and economic outcomes of patients with Gram-negative (GN) LRTIs treated in intensive care units (ICUs).

METHODS

This was a retrospective, observational, cross-sectional study of adult patients treated in ICUs at two large academic medical centers in metropolitan Detroit, Michigan, from October 2013 to October 2015. To meet the inclusion criteria, patients must have had CDC-defined LRTI caused by a GN pathogen during ICU stay. Microbiological assessment of available Pseudomonas aeruginosa isolates included minimum inhibitory concentrations for key antimicrobial agents.

RESULTS

Four hundred and seventy-two patients, primarily from the community (346, 73.3%), were treated in medical ICUs (272, 57.6%). Clinically defined pneumonia was common (264, 55.9%). Six hundred and nineteen GN organisms were identified from index respiratory cultures: P. aeruginosa was common (224, 36.2%), with 21.6% of these isolates being multidrug resistant. Cefepime (213, 45.1%) and piperacillin/tazobactam (174, 36.8%) were the most frequent empiric GN therapies. Empiric GN therapy was inappropriate in 44.6% of cases. Lack of in vitro susceptibility (80.1%) was the most common reason for inappropriateness. Patients with inappropriate empiric GN therapy had longer overall stay, which translated to a median total cost of care of $79,800 (interquartile range $48,775 to $129,600) versus $68,000 (interquartile range $38,400 to $116,175), p = 0.013. Clinical failure (31.5% vs 30.0%, p = 0.912) and in-hospital all-cause mortality (26.4% vs 25.9%, p = 0.814) were not different.

CONCLUSION

Drug-resistant pathogens were frequently found and empiric GN therapy was inappropriate in nearly 50% of cases. Inappropriate therapy led to increased lengths of stay and was associated with higher costs of care.

Inapparent Outbreaks of Ventilator-Associated Pneumonia An Ecologic Analysis of Prevention and Cohort Studies

Objective:

To compare ventilator-associated pneumonia (VAP) rates and patterns of isolates across studies of antibiotic and non-antibiotic methods for preventing VAP.

Design:

With the use of 42 cohort study groups as the reference standard, the prevalence of VAP was modeled in two linear regressions: one with the control groups and the other with the intervention groups of 96 VAP prevention studies. The proportion of patients admitted with trauma and the VAP diagnostic criteria were used as ecologic correlates. Also, the patterns of pathogenic isolates were available for 117 groups.

Results:

In the first regression model, the VAP rates for the control groups of antibiotic-based prevention studies were at least 18 (CI95, 12 to 24) per 100 patients higher than those in the cohort study groups (P< .001). By contrast, comparisons of cohort study groups with all other control and intervention groups in the first and second regression models yielded differences that were less than 6 per 100 and not significant (P> .05). For control groups with VAP rates greater than 35%, the patterns of VAP isolates, such as the proportion ofStaphylococcus aureus,more closely resembled those in the corresponding intervention groups than in the cohort groups.

Conclusions:

The rates of VAP in the control groups of the antibiotic prevention studies were significantly higher than expected and the patterns of pathogenic isolates were unusual. These observations suggest that inapparent outbreaks of VAP occurred in these studies. The possibility remains that antibiotic-based VAP prevention presents a major cross-infection hazard.

Bacteriological Monitoring of Water Reservoirs in Oxygen Humidifiers: Safety of Prolonged and Multipatient Use of Prefilled Disposable Oxygen Humidifier Bottles

Bacterial colony counts in water specimens from oxygen humidifiers that used reusable water reservoirs were compared with counts in water specimens from humidifiers that used prefilled disposable reservoir bottles to evaluate the effects of prolonged and multipatient use of humidifiers. Bacteria were detected after 1 week of operation in water specimens collected from many humidifiers with reusable reservoirs, but no bacteria were detected in water specimens from disposable bottles for up to 12 weeks during use of the humidifier by multiple patients.

Lack of impact of selective digestive decontamination on Pseudomonas aeruginosa ventilator-associated pneumonia: benchmarking the evidence base

BACKGROUND

The selective digestive decontamination (SDD) component antibiotics have activity against Pseudomonas aeruginosa, an important ventilator-associated pneumonia (VAP) isolate. Evaluating the relationship between the anti-pseudomonal activity of SDD towards its VAP prevention effect is complicated by postulated indirect effects of SDD mediated in the concurrent control groups. The objective here is to address these effects through a benchmarking analysis of the evidence base.

METHODS

Forty-eight observational studies of VAP incidence and 43 interventional studies of SDD and other methods of VAP prevention were sourced from 10 reviews. The P. aeruginosa isolate proportion (P. aeruginosa-IP) data were summarized by meta-analysis using random effects methods. The mode of VAP diagnosis, proportion of trauma admissions and the intervention method under study were examined in meta-regression models as potential group-level predictors of P. aeruginosa-IP.

RESULTS

The mean P. aeruginosa-IP derived from the observational studies (the benchmark) is 22.3% [95% confidence interval (CI) 19.8%-25.2%] versus 19.6% (95% CI 15.6%-24.4%) and 20.8% (95% CI 14.6%-28.5%) for concurrent control groups and intervention groups of SDD studies, respectively. In the meta-regression models, the proportion of trauma admissions is negatively correlated with P. aeruginosa-IP, whereas membership of neither a concurrent control nor intervention group of an SDD study is negatively correlated.

CONCLUSIONS

There is no evidence for either direct or indirect effects of SDD on P. aeruginosa-IP that could account for the profound effects of SDD on VAP incidence.

Profound effect of study design factors on ventilator-associated pneumonia incidence of prevention studies: benchmarking the literature experience

BACKGROUND

The ventilator-associated pneumonia incident proportion (VAP-IP) is highly variable among control groups of studies of methods for its prevention. The objective here is to develop and validate a literature-derived benchmark against which these groups can be profiled.

METHODS

A literature search yielded 95 cohort groups and control and intervention groups of 150 studies of either non-antimicrobial or antimicrobial methods of VAP prevention. The 95 cohort groups comprise a benchmark set (30 groups), from which the reference funnel plot (RFP) was derived, and a search set (65 groups), against which the benchmark was validated. The VAP-IP data of the benchmark set were found in five published systematic reviews, whereas the VAP-IP data of the search set were abstracted directly from the literature.

FINDINGS

Among the 95 cohort groups, the VAP-IP of groups with size >399 was significantly lower than the VAP-IP of smaller groups. Compared with the RFP, 15 of 51 (29%) control groups from studies of antimicrobial methods of VAP prevention with concurrent design were high outlier versus 2 of 110 (2%) control groups from other types of study design (P < 0.001). There were only 22 (14%) outlier groups, all low outlier, among the 162 intervention groups.

CONCLUSIONS

Study design factors such as concurrency and study size have potentially greater influence on the VAP-IP than do the VAP prevention methods under study. The outlier status of control groups were inapparent in the individual studies and the meta-analyses and yet would have confounded the estimates of treatment effect.

Nosocomial pneumonia : rationalizing the approach to empirical therapy

Nosocomial pneumonia or hospital-acquired pneumonia (HAP) causes considerable morbidity and mortality. It is the second most common nosocomial infection and the leading cause of death from hospital-acquired infections. In 1996 the American Thoracic Society (ATS) published guidelines for empirical therapy of HAP. This review focuses on the literature that has appeared since the ATS statement. Early diagnosis of HAP and its etiology is crucial in guiding empirical therapy. Since 1996, it has become clear that differentiating mere colonization from etiologic pathogens infecting the lower respiratory tract is best achieved by employing bronchoalveolar lavage (BAL) or protected specimen brush (PSB) in combination with quantitative culture and detection of intracellular microorganisms. Endotracheal aspirate and non-bronchoscopic BAL/PSB in combination with quantitative culture provide a good alternative in patients suspected of ventilator-associated pneumonia. Since culture results take 2-3 days, initial therapy of HAP is by definition empirical. Epidemiologic studies have identified the most frequently involved pathogens: Enterobacteriaceae, Haemophilus influenzae, Streptococcus pneumoniae and Staphylococcus aureus ('core pathogens'). Empirical therapy covering only the 'core pathogens' will suffice in patients without risk factors for resistant microorganisms. Studies that have appeared since the ATS statement issued in 1996, demonstrate several new risk factors for HAP with multiresistant pathogens. In patients with risk factors, empirical therapy should consist of antibacterials with a broader spectrum. The most important risk factors for resistant microorganisms are late onset of HAP (>/=5 days after admission), recent use of antibacterial therapy, and mechanical ventilation. Multiresistant bacteria of specific interest are methicillin-resistant S. aureus (MRSA), Pseudomonas aeruginosa, Acinetobacter calcoaceticus-baumannii, Stenotrophomonas maltophilia and extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae. Each of these organisms has its specific susceptibility pattern, demanding appropriate antibacterial treatment. To further improve outcomes, specific therapeutic options for multiresistant pathogens and pharmacological factors are discussed. Antibacterials developed since 1996 or antibacterials with renewed interest (linezolid, quinupristin/dalfopristin, teicoplanin, meropenem, new fluoroquinolones, and fourth-generation cephalosporins) are discussed in the light of developing resistance.Since the ATS statement, many reports have shown increasing incidences of resistant microorganisms. Therefore, one of the most important conclusions from this review is that empirical therapy for HAP should not be based on general guidelines alone, but that local epidemiology should be taken into account and used in the formulation of local guidelines.

Efficacy of adequate early antibiotic therapy in ventilator-associated pneumonia: influence of disease severity

OBJECTIVE

To test the hypothesis that the outcome of patients with ventilator-associated pneumonia (VAP) depends on both their baseline severity at VAP onset and the adequacy of empirical antibiotic therapy.

DESIGN AND SETTING

Prospective clinical study in six intensive care units in Paris, France.

PATIENTS

One hundred and forty-two patients with VAP after >/= 48 h of mechanical ventilation.

MEASUREMENTS AND RESULTS

Patients were compared according to whether adequate antibiotics were started when VAP was first suspected (D0). At day 0, the rate of adequate antibiotic therapy was 44.4% and rose to 92% at day 2. Outcomes were recorded at the ICU and hospital discharge. Overall, no significant mortality difference was found with and without adequate early antibiotics. When patients were also classified based on the initial Logistic Organ Dysfunction score (LOD), mortality was significantly higher with inadequate early antibiotic therapy in the groups with LOD </= 4 (ICU mortality: 37% vs 7%, P=0.006; hospital mortality: 44% vs 15%, P=0.01). A multivariate logistic regression confirmed that inadequate antibiotic therapy increased mortality in patients with LOD </= 4 after adjustment on other prognostic factors.

CONCLUSIONS

Inadequate empirical treatment seemed to be associated with a poor prognosis only in patients with LOD </= 4. These results need to be confirmed by further studies before any reappraisal of current guidelines for empirical antibiotic therapy of VAP can be envisaged.

Prolonged use of heat and moisture exchangers does not affect device efficiency or frequency rate of nosocomial pneumonia

OBJECTIVE

To determine whether use of a single heat and moisture exchanger (HME) for < or =120 hrs affects efficiency, resistance, level of bacterial colonization, frequency rate of nosocomial pneumonia, and cost compared with changing the HME every 24 hrs.

DESIGN

Prospective, controlled, randomized, unblinded study.

SETTING

Surgical intensive care unit at a university teaching hospital.

PATIENTS

A total of 220 consecutive patients requiring mechanical ventilation for >48 hrs.

INTERVENTIONS

Patients were randomized to one of three groups: a) hygroscopic HME (Aqua+) changed every 24 hrs (HHME-24); b) hydrophobic HME (Duration HME) changed every 120 hrs (HME-120); and c) hygroscopic HME (Aqua+) changed every 120 hrs (HHME-120). Devices in all groups could be changed at the discretion of the staff when signs of occlusion or increased resistance were identified.

MEASUREMENTS AND MAIN RESULTS

Daily measurements of inspired gas temperature, inspired relative humidity, and device resistance were made. Additionally, daily cultures of the patient side of the device were accomplished. The frequency rate of nosocomial pneumonia was made by using clinical criteria. Ventilatory support variables, airway care, device costs, and clinical indicators of humidification efficiency (sputum volume, sputum efficiency) were also recorded. Prolonged use of both hygroscopic and hydrophobic devices did not diminish efficiency or increase resistance. There was no difference in the number of colony-forming units from device cultures over the 5-day period and no difference between colony-forming units in devices changed every 24 hrs compared with devices changed after 120 hrs. The average duration of use was 23+/-4 hrs in the HHME-24 group, 73+/-13 hrs in the HME-120 group, and 74+/-9 hrs in the HHME-120 group. Mean absolute humidity was greater for the hygroscopic devices (30.4+/-1.1 mg of H2O/L) compared with the hydrophobic devices (27.8+/-1.3 mg of H2O/L). The frequency rate of nosocomial pneumonia was 8% (8:100) in the HHME-24 group, 8.3% (5:60) in the HME-120 group, and 6.6% (4:60) in the HHME-120 group. Pneumonia rates per 1000 ventilatory support days were 20:1000 in the HHME-24 group, 20.8:1000 in the HME-120 group, and 16.6:1000 in the HHME-120 group. Costs per day were $3.24 for the HHME-24 group, $2.98 for the HME-120 group, and $1.65 for the HHME-120 group.

CONCLUSIONS

Changing the hydrophobic or hygroscopic HME after 3 days does not diminish efficiency, increase resistance, or alter bacterial colonization. The frequency rate of nosocomial pneumonia was also unchanged. Use of HMEs for >24 hrs, up to 72 hrs, is safe and cost effective.

Supine body position as a risk factor for nosocomial pneumonia in mechanically ventilated patients: a randomised trial

BACKGROUND

Risk factors for nosocomial pneumonia, such as gastro-oesophageal reflux and subsequent aspiration, can be reduced by semirecumbent body position in intensive-care patients. The objective of this study was to assess whether the incidence of nosocomial pneumonia can also be reduced by this measure.

METHODS

This trial was stopped after the planned interim analysis. 86 intubated and mechanically ventilated patients of one medical and one respiratory intensive-care unit at a tertiary-care university hospital were randomly assigned to semirecumbent (n=39) or supine (n=47) body position. The frequency of clinically suspected and microbiologically confirmed nosocomial pneumonia (clinical plus quantitative bacteriological criteria) was assessed in both groups. Body position was analysed together with known risk factors for nosocomial pneumonia.

FINDINGS

The frequency of clinically suspected nosocomial pneumonia was lower in the semirecumbent group than in the supine group (three of 39 [8%] vs 16 of 47 [34%]; 95% CI for difference 10.0-42.0, p=0.003). This was also true for microbiologically confirmed pneumonia (semirecumbent 2/39 [5%] vs supine 11/47 [23%]; 4.2-31.8, p=0.018). Supine body position (odds ratio 6.8 [1.7-26.7], p=0.006) and enteral nutrition (5.7 [1.5-22.8], p=0.013) were independent risk factors for nosocomial pneumonia and the frequency was highest for patients receiving enteral nutrition in the supine body position (14/28, 50%). Mechanical ventilation for 7 days or more (10.9 [3.0-40.4], p=0.001) and a Glasgow coma scale score of less than 9 were additional risk factors.

INTERPRETATION

The semirecumbent body position reduces frequency and risk of nosocomial pneumonia, especially in patients who receive enteral nutrition. The risk of nosocomial pneumonia is increased by long-duration mechanical ventilation and decreased consciousness.

Role of different routes of tracheal colonization in the development of pneumonia in patients receiving mechanical ventilation

STUDY OBJECTIVE

To evaluate the importance of the different pathogenic pathways involved in the development of ventilator-associated pneumonia (VAP).

DESIGN

Prospective study.

SETTING

An 18-bed medical and surgical ICU.

PATIENTS

One hundred twenty-three patients receiving mechanical ventilation (MV).

INTERVENTIONS

Tracheal, pharyngeal, and gastric samples were obtained simultaneously every 24 h. In cases where VAP was suspected clinically, bronchoscopy with protected specimen brush and BAL were performed. Semiquantitative cultures of pharyngeal samples and quantitative cultures for the remaining samples were obtained.

RESULTS

Tracheal colonization at some time during MV was observed in 110 patients (89%). Eighty patients had initial colonization, 34 patients had primary colonization, and 50 patients had secondary colonization. Nineteen patients had VAP, and 25 organisms were isolated. For none of these organisms was the stomach the initial site of colonization. Gram-positive organisms colonized mainly in the trachea during the first 24 h of MV (p<0.001). On the contrary, enteric Gram-negative bacilli (p<0.001) and yeasts (p<0.002) colonized the trachea secondarily. Previous endotracheal intubation (p<0.005) and acute renal failure before admission to the ICU (p<0.001) were associated with colonization by Pseudomonas aeruginosa; prior antibiotics were associated with colonization by Acinetobacter baumanii (p<0.05) and yeasts (p<0.006); and cranial trauma was associated with Staphylococcus aureus colonization (p<0.035).

CONCLUSIONS

Although the stomach can be a source of organisms that colonize the tracheobronchial tree, it is a much less common source of the bacteria that cause VAP. The pattern of colonization and risk factors may be different according to the type of organisms involved.

Early diagnosis of ventilator-associated pneumonia. Is it possible to define a cutoff value of infected cells in BAL fluid?

STUDY OBJECTIVE

To assess the usefulness of quantification of infected cells (ICs) in BAL fluid for the diagnosis of ventilator-associated pneumonia (VAP).

DESIGN

A prospective study.

SETTING

A medico-surgical ICU in a tertiary health-care institution.

PATIENTS

One hundred thirty-two patients (mean age, 52 +/- 19 years). The suspicion of nosocomial pneumonia was strong in these patients: all had fever (> or = 38.5 degrees C), purulent tracheal aspirates, leukocytosis (> or = 10,000 cells per cubic millimeter), and new or persistent radiographic lung infiltrates.

INTERVENTIONS

One hundred sixty-three samples (BAL and protected specimen brushes [PSB]) were obtained.

RESULTS

VAP was present in 56 cases. The diagnosis was excluded in the remaining 107 cases. The IC count was performed on 100 cells in BAL fluid. The percentage of IC was significantly higher (12.6 +/- 12.4 vs 1.14 +/- 3.39; p < 0.0001) in patients with pneumonia: the area under the receiver operating characteristic (ROC) curve was 0.888 and a threshold of 2% of IC corresponded to a sensitivity of 84%, a specificity of 80%, a positive predictive value of 69%, and a negative predictive value of 90%.

CONCLUSIONS

It is possible to define a threshold of IC in BAL fluid with a good reliability by using an ROC curve. This technique is useful for the early diagnosis (< 2 h) of nosocomial bacterial pneumonia in mechanically ventilated patients and allows a rapid and appropriate treatment of most of the patients with suspected VAP.

Aspiration of oral feedings in patients with tracheostomies

Oral feeding aspiration can be a threat to positive outcomes for patients with tracheostomy who require mechanical ventilation. A review of current literature reveals a high incidence of aspiration in this population. Silent aspiration is particularly common, meaning that beside evaluations of swallowing function often are unreliable. Advanced practice nurses who are aware of the risk factors for aspiration may be able to improve outcomes for this population. This article presents a review of the literature on oral feeding aspiration in patients with tracheostomies, suggests areas of additional research, and provides nursing implications for the safe care of these patients.

Burkholderia cepacia respiratory tract acquisition: epidemiology and molecular characterization of a large nosocomial outbreak

In 1994 we investigated a large outbreak of Burkholderia (formerly Pseudomonas) cepacia respiratory tract acquisition. A case patient was defined as any patient with at least one sputum culture from which B. cepacia was isolated from 1 January to 31 December 1994. Seventy cases were identified. Most (40 [61%]) occurred between 1 February and 31 March 1994; of these, 35 (86%) were mechanically ventilated patients, 30 of whom were in an intensive-care unit (ICU) when B. cepacia was first isolated. Compared with control patients who were mechanically ventilated in an ICU, these 30 case-patients were significantly more likely to have been ventilated for 2 or more days (30/30 v. 15/30; P < 0.001) or to have been intubated more than once (12/30 v. 2/30; OR = 9.3, 95% CI 1.6-68.8; P = 0.002) before the first isolation of B. cepacia. By multivariate analysis, the 35 mechanically ventilated case-patients were significantly more likely to have received a nebulized medication (OR = 11.9, 95% CI = 1.6-553.1; P < 0.001) and a cephalosporin antimicrobial (OR = 11.9, 95% CI = 1.6-553.1) in the 10 days before the first isolation of B. cepacia, compared with B. cepacia-negative control-patients matched by date and duration of most recent mechanical ventilation. Although B. cepacia was not cultured from medications or the hospital environment, all outbreak strains tested had an identical DNA restriction endonuclease digestion pattern by pulsed-field gel electrophoresis. Review of respiratory therapy procedures revealed opportunities for contamination of nebulizer reservoirs. This investigation suggests that careful adherence to standard procedures for administration of nebulized medications is essential to prevent nosocomial respiratory infections.

Epidemiology of infection in ICUs

Patients admitted to ICUs are at the greatest risk of acquiring nosocomial infections, partly because of their serious underlying disease, but also by exposure to life-saving invasive procedures. Nosocomial infections increase patient morbidity, increase the length of hospital stay and hospital costs, and may increase mortality rates. When serious infections are suspected, treatment must be commenced immediately to increase the likelihood of a satisfactory outcome for the patient. Empirical knowledge, to select appropriate antibiotics, must be used so that the most likely infecting organisms are treated. In the past this has meant that antibiotics with activity against Gram-negative pathogens were most likely to be selected. However, infections where Gram-positive pathogens are responsible (e.g. Staphylococcus aureus, Staphylococcus epidermidis and enterococci) are increasingly being found. The European Prevalence of Infection in Intensive Care Study (EPIC), the largest point-prevalence study of infection in ICUs in Western Europe was carried out on 28 April 1992. Data on 10,038 patients in 1417 adult ICU departments from 17 countries was collected and analysed. Of the ICU patients surveyed, 21% had at least one infection acquired in an ICU. The most common infections acquired in an ICU were pneumonia (47%), other infections of the lower respiratory tract (18%), infections of the urinary tract (18%) and infections of the blood-stream (12%). The bacterial isolates were equally divided between Gram-negative and Gram-positive species. The commonly reported bacteria were Enterobacteriaceae (34%), S. aureus (30%), Pseudomonas aeruginosa (29%), coagulase-negative staphylococci (19%) and enterococci (12%).