Epidemiology of nosocomial ventilator-associated pneumonia

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.

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 β-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.

The perfidious effect of topical placebo: calibration of Staphylococcus aureus ventilator-associated pneumonia incidence within selective digestive decontamination studies versus the broader evidence base

Among various methods for preventing ventilator-associated pneumonia (VAP), the evidence base for selective digestive decontamination (SDD) appears most compelling. However, the extent of Staphylococcus aureus emergence with SDD use remains uncertain. Groups from 37 observational studies and component (control and intervention) groups from 58 studies of SDD and other methods of VAP prevention were sourced exclusively from 10 systematic reviews. S. aureus as a proportion of VAP isolates (S. aureus isolate proportion [S. aureus IP]) among component groups was calibrated versus that among observational groups (the benchmark). The influence of topical placebo used for blinding purposes and other group-level factors was estimated using generalized estimating equation methods (GEE). The mean S. aureus IP is 22% (95% confidence interval [CI], 19 to 25) for 37 observational groups versus 32% (24 to 41) and 20% (15 to 25) for 22 control groups from the SDD evidence base which did versus did not receive topical placebo, respectively. In GEE models including all 148 observational and component groups, membership of a control (P = 0.03) or intervention (P < 0.001) group of an SDD study that used topical placebo was associated with higher S. aureus IP, whereas, in contrast, membership of these groups was without effect on Pseudomonas aeruginosa. Topical placebo is implicated as a vehicle for selective cross-infection with S. aureus within the specific context of the SDD evidence base. This effect of topical placebo is perfidious; it could contribute to the higher VAP incidence and inflate the apparent "effectiveness" of SDD. The SDD evidence base requires reappraisal.

Paradoxical ventilator associated pneumonia incidences among selective digestive decontamination studies versus other studies of mechanically ventilated patients: benchmarking the evidence base

Introduction

Selective digestive decontamination (SDD) appears to have a more compelling evidence base than non-antimicrobial methods for the prevention of ventilator associated pneumonia (VAP). However, the striking variability in ventilator associated pneumonia-incidence proportion (VAP-IP) among the SDD studies remains unexplained and a postulated contextual effect remains untested for.

Methods

Nine reviews were used to source 45 observational (benchmark) groups and 137 component (control and intervention) groups of studies of SDD and studies of three non-antimicrobial methods of VAP prevention. The logit VAP-IP data were summarized by meta-analysis using random effects methods and the associated heterogeneity (tau²) was measured. As group level predictors of logit VAP-IP, the mode of VAP diagnosis, proportion of trauma admissions, the proportion receiving prolonged ventilation and the intervention method under study were examined in meta-regression models containing the benchmark groups together with either the control (models 1 to 3) or intervention (models 4 to 6) groups of the prevention studies.

Results

The VAP-IP benchmark derived here is 22.1% (95% confidence interval; 95% CI; 19.2 to 25.5; tau² 0.34) whereas the mean VAP-IP of control groups from studies of SDD and of non-antimicrobial methods, is 35.7 (29.7 to 41.8; tau² 0.63) versus 20.4 (17.2 to 24.0; tau² 0.41), respectively (P < 0.001). The disparity between the benchmark groups and the control groups of the SDD studies, which was most apparent for the highest quality studies, could not be explained in the meta-regression models after adjusting for various group level factors. The mean VAP-IP (95% CI) of intervention groups is 16.0 (12.6 to 20.3; tau² 0.59) and 17.1 (14.2 to 20.3; tau² 0.35) for SDD studies versus studies of non-antimicrobial methods, respectively.

Conclusions

The VAP-IP among the intervention groups within the SDD evidence base is less variable and more similar to the benchmark than among the control groups. These paradoxical observations cannot readily be explained. The interpretation of the SDD evidence base cannot proceed without further consideration of this contextual effect.

Bacterial Infections

In Osier’s time, bacterial pneumonia was a dreaded event, so important that he borrowed John Bunyan’s characterization of tuberculosis and anointed the pneumococcus, as the prime pathogen, “Captain of the men of death.”1 One hundred years later much has changed, but much remains the same. Pneumonia is now the sixth most common cause of death and the most common lethal infection in the United States. Hospital-acquired pneumonia is now the second most common nosocomial infection.2 It was documented as a complication in 0.6% of patients in a national surveillance study,3 and has been reported in as many as 20% of patients in critical care units.4 Furthermore, it is the leading cause of death among nosocomial infections.5 Leu and colleagues6 were able to associate one third of the mortality in patients with nosocomial pneumonia to the infection itself. The increase in hospital stay, which averaged 7 days, was statistically significant. It has been estimated that nosocomial pneumonia produces costs in excess of $500 million each year in the United States, largely related to the increased length of hospital stay.

Effectiveness of an Educational Program to Reduce Ventilator-Associated Pneumonia in a Tertiary Care Center in Thailand: A 4-Year Study

BACKGROUND

Ventilator-associated pneumonia (VAP) is considered to be an important cause of infection-related death and morbidity in intensive care units (ICUs). We sought to determine the long-term effect of an educational program to prevent VAP in a medical ICU (MICU).

METHODS

A 4-year controlled, prospective, quasi-experimental study was conducted in an MICU, surgical ICU (SICU), and coronary care unit (CCU) for 1 year before the intervention (period 1), 1 year after the intervention (period 2), and 2 follow-up years (period 3). The SICU and CCU served as control ICUs. The educational program involved respiratory therapists and nurses and included a self-study module with preintervention and postintervention assessments, lectures, fact sheets, and posters.

RESULTS

Before the intervention, there were 45 episodes of VAP (20.6 cases per 1000 ventilator-days) in the MICU, 11 (5.4 cases per 1000 ventilator-days) in the SICU, and 9 (4.4 cases per 1000 ventilator-days) in the CCU. After the intervention, the rate of VAP in the MICU decreased by 59% (to 8.5 cases per 1000 ventilator-days; P=.001) and remained stable in the SICU (5.6 cases per 1000 ventilator-days; P=.22) and CCU (4.8 cases per 1000 ventilator-days; P=.48). The rate of VAP in the MICU continued to decrease in period 3 (to 4.2 cases per 1000 ventilator-days; P=.07), and rates in the SICU and CCU remained unchanged. Compared with period 1, the mean duration of hospital stay in the MICU was reduced by 8.5 days in period 2 (P<.001) and by 8.9 days in period 3 (P<.001). The monthly hospital antibiotic costs of VAP treatment and the hospitalization cost for each patient in the MICU in periods 2 and 3 were also reduced by 45%-50% (P<.001) and 37%-45% (P<.001), respectively.

CONCLUSIONS

A focused education intervention resulted in sustained reductions in the incidence of VAP, duration of hospital stay, cost of antibiotic therapy, and cost of hospitalization.

Nosocomial infections in neurocritical care

Development of nosocomial infections is a commonly encountered problem for critically ill patients. Approximately half of all nosocomial pneumonias in the neurointensive care unit (NICU) are associated with ventilator-associated pneumonia. Prompt diagnosis with appropriate specimen analysis is required in order to prevent increased morbidity. Catheter-related blood stream infection imposes financial as well as medical implications. Multifaceted interventions are helpful to ensure adherence with evidence-based infection control guidelines. Urosepsis occurs in approximately 16% of patients. Colonized patients without evidence of infection do not require treatment, but the indwelling catheter should be changed. NICU patients have increased risk of developing cerebrospinal fluid infection due to frequent placement of external ventricular drains. The incidence of ventriculostomy-related meningitis or ventriculitis is approximately 8%. It is unclear whether the duration of ventricular catheter has any relationship with the risk of infection. Patients often receive multiple antibiotics, leading to an increased risk of developing Clostridium difficile colitis, which needs prompt diagnosis and appropriate antimicrobial therapy.

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.

Ventilator-associated pneumonia in extremely preterm neonates in a neonatal intensive care unit: characteristics, risk factors, and outcomes

OBJECTIVE

To determine the rates, characteristics, risk factors, and outcomes of ventilator-associated pneumonia (VAP) in extremely preterm neonates in a neonatal intensive care unit (NICU).

METHODS

A prospective cohort study was conducted at the St Louis Children's Hospital on all patients who had birth weight <or=2000 g and were admitted to the NICU for >or=48 hours from October 2000 to July 2001. Extremely preterm neonates were defined as neonates with estimated gestational age (EGA) <28 weeks. The primary outcome was the development of VAP. Secondary outcomes were death and NICU length of stay (LOS). Multiple logistic regression was performed to determine independent predictors for VAP and mortality.

RESULTS

A total of 229 patients were enrolled. Sixty-seven (29%) had EGA <28 weeks. Nineteen episodes of VAP occurred in 19 (28.3%) of 67 mechanically ventilated patients. VAP rates were 6.5 per 1000 ventilator days for patients with EGA <28 weeks and 4 per 1000 ventilator days for EGA >or=28 weeks. By multivariate analysis, bloodstream infection before VAP (adjusted odds ratio: 3.5; 95% confidence interval [CI]: 1.2-10.8) was an independent risk factor for VAP after adjustment for the duration of endotracheal intubation. Ventilator-associated pneumonia (adjusted odds ratio: 3.4; 95% CI: 1.2-12.3) was an independent predictor of mortality. A strong association between VAP and mortality was observed in neonates who stayed in the NICU >30 days (relative risk: 8.0; 95% CI: 1.9-35.0). Patients with VAP also had prolonged NICU LOS (median: 138 vs 82 days).

CONCLUSIONS

VAP occurred at high rates in extremely preterm neonates and was associated with increased mortality. Additional studies are needed to develop interventions to prevent VAP in NICU patients.

Ventilator-associated pneumonia in pediatric intensive care unit patients: risk factors and outcomes

OBJECTIVES

To determine the rates, risk factors, and outcomes of ventilator-associated pneumonia in pediatric intensive care unit (PICU) patients.

METHODS

A prospective cohort study was conducted at the St Louis Children's Hospital PICU on all patients who were admitted to the PICU from September 1, 1999, to May 31, 2000, except those who died within 24 hours, were > or =18 years of age, or were neonatal intensive care unit patients on extracorporeal membrane oxygenation. The primary outcome measured was the development of ventilator-associated pneumonia. Secondary outcomes were death and hospital and PICU length of stay. Multiple logistic regression analysis was performed to determine independent predictors for ventilator-associated pneumonia.

RESULTS

There were 34 episodes of ventilator-associated pneumonia in 30 patients of 911 admissions (3.3%) and 595 (5.1%) mechanically ventilated patients. The mean ventilator-associated pneumonia rate was 11.6/1000 ventilator days. By logistic regression analysis, genetic syndrome (odds ratio [OR]: 2.37; 95% confidence interval [CI]: 1.01-5.46), reintubation (OR: 2.71; 95% CI: 1.18-6.21), and transport out of the PICU (OR: 8.90; 95% CI: 3.82-20.74) independently predicted ventilator-associated pneumonia.

CONCLUSIONS

Ventilator-associated pneumonia occurs at significant rates among mechanically ventilated PICU patients and is associated with processes of care. Additional studies are necessary to develop interventions to prevent ventilator-associated pneumonia.

Risk factors for nosocomial pneumonia. Focus on prophylaxis

Despite an increased understanding of the pathogenesis of NP and advances in diagnosis and treatment, the risk, cost, morbidity, and mortality of NP remain unacceptably high. This article has identified strategic areas for primary and secondary prophylaxis that are simple and cost-effective. Realizing that the pathogenesis of NP requires bacterial colonization and the subsequent entry of these bacteria into the lower respiratory tree helps highlight the role of cross-infection and the importance of standard infection control procedures. Similarly the role of sedation and devices as risk factors can be reduced by minimizing the duration and intensity of sedation and length of exposure to invasive devices. Additional low-cost interventions that have been shown to be effective in preventing NP are the positioning of patients in a semirecumbent position and the appropriate use of enteral feeding, antibiotics, and selected medical devices. Prophylaxis of NP and VAP is carried out best by a multidisciplinary management team comprised of physicians (critical care, pulmonary medicine, infectious diseases, and primary care), critical care and infection control nurses, and respiratory therapists, even though this approach may result in decreased professional autonomy and freedom. This group should review the current guidelines, pathways, and standards for short-term and long-term prophylaxis of NP and VAP, then integrate them into and monitor their use for routine patient care. The risk factors and prophylaxis strategies for NP discussed in this article apply primarily to patients in acute care facilities, but also are relevant to alternative health care settings as well as the care of ill patients in ambulatory settings. The routine use of effective team policies for prophylaxis needs to be monitored by the Joint Commission for the Accreditation of Health Care or other agencies. Research to delineate the most effective and feasible strategies for prophylaxis NP has been compromised by insufficient funding and lack of adequate, randomized multicenter studies to enable generalizability of results. Effective strategies for prophylaxis have not been disseminated widely or implemented in hospitals. Successful short-term and long-term strategies for prophylaxis must be evaluated and implemented by a team of physicians, nurses, and respiratory therapists. More than 100 years ago, Sir William Osler warned health care providers, "Remember how much you don't know." The authors would add that clinicians have acquired significant knowledge about risk factors and prophylaxis of NP in the 1980s and 1990s, but prophylaxis as a theory rather than an action. If the tree has not been planted, the time is now.

Antibiotic therapy of ventilator-associated pneumonia--a reappraisal of rationale in the era of bacterial resistance

Ventilator-associated pneumonia (VAP) is the most frequent nosocomial infection in intensive care units (ICU). Resistance patterns seen in ICUs suggest that prescribing recommendations should be reappraised to limit practices engendering resistance to large families of antibiotics. Despite concern surrounding the use of antibiotics in the management of VAP, there is limited evidence to assist the clinician in making decisions about the indications for such therapy, the selection of the correct antibiotic(s), the timing of initiation of therapy and its duration. The high amount of antibiotic use, in combination with the low grade colonisation of patients with multi-resistant pathogens at the time of admission, turns the ICU into an environment where antibiotic policy is likely to have an effect on the resistance problem. Opinions are changing as to the validity of invasive techniques in guiding prescribing decisions. Invasive and semi-invasive diagnostic testing increases physician confidence in the diagnosis and management of VAP and helps to limit or discontinue antibiotic treatment.

Effectiveness and cost of selective decontamination of the digestive tract in critically ill intubated patients. A randomized, double-blind, placebo-controlled, multicenter trial

We evaluated the effect of selective decontamination of the digestive tract (SDD) on the incidence of ventilator-associated pneumonia (VAP) and its associated morbidity and cost in a mixed population of intubated patients. Two hundred seventy-one consecutive patients admitted to the intensive care units (ICUs) of five teaching hospitals and who had an expected need for intubation exceeding 48 h were enrolled and received topical antibiotics or placebo. Uninfected patients additionally received ceftriaxone or placebo for 3 d. VAP occurred in 11.4% of SDD-treated and 29.3% of control-group patients (p < 0.001; 95% confidence interval [CI]: 7.8 to 27.9). The incidence of nonrespiratory infections in the two groups was 19.1% and 30.7%, respectively (p = 0.04; 95% CI: 0.7 to 22.7). Among survivors, the median length of ICU stay was 11 d (interquartile range: 7 to 21.5 d) for the SDD-treated group and 16. 5 d (10 to 30 d) for the control group (p = 0.006). Mean cost per survivor was $11,926 for treated and $16,296 for control-group patients. Mortality was 38.9% and 47.1%, respectively (p = 0.57). In decontaminated patients, the prevalence of gram-negative bacilli fell within 7 d from 47.4% to 13.0% (p < 0.001), whereas colonization with resistant gram-positive strains was higher (p < 0. 05) than in the placebo group. In a mixed population of intubated patients, SDD was associated with a significant reduction of morbidity at a reduced cost. Our findings support the use of SDD in this high-risk group.

Nosocomial pneumonia in patients with acute respiratory distress syndrome

To describe the epidemiologic and microbial aspects of ventilator-associated pneumonia (VAP) in patients with acute respiratory distress syndrome (ARDS), we prospectively evaluated 243 consecutive patients who required mechanical ventilation (MV) for > or = 48 h, 56 of whom developed ARDS as defined by a Murray lung injury score > 2.5. We did this with bronchoscopic techniques when VAP was clinically suspected, before any modification of existing antimicrobial therapy. For all patients, the diagnosis of pneumonia was established on the basis of culture results of protected-specimen brush (PSB) (> or = 10(3) cfu/ml) and bronchoalvelolar lavage fluid (BALF) (> or = 10(4) cfu/ml) specimens, and direct examination of cells recovered by bronchoalveolar lavage (BAL) (< or = 5% of infected cells). Thirty-one (55%) of the 56 patients with ARDS developed VAP for a total of 41 episodes, as compared with only 53 (28%) of the 187 patients without ARDS for a total of 65 episodes (p = 0.0005). Only 10% of first episodes of VAP in patients with ARDS occurred before Day 7 of MV, as compared with 40% of the episodes in patients without ARDS (p = 0.005). All but two patients with ARDS who developed VAP had received antimicrobial treatment (mostly with broad-spectrum antibiotics) before the onset of infection, as compared with only 35 patients without ARDS (p = 0.004). The organisms most frequently isolated from patients with ARDS and VAP were methicillin-resistant Staphylococcus aureus (23%), nonfermenting gram-negative bacilli (21%), and Enterobacteriaceae (21%). These findings confirm that microbiologically provable VAP occurs far more often in patients with ARDS than in other ventilated patients. Because these patients are often treated with antibiotics early in the course of the syndrome, the onset of VAP is frequently delayed after the first week of MV, and is then caused mainly by methicillin-resistant S. aureus and other multiresistant microorganisms.

Reducing the incidence of ventilator-related pneumonia

Ventilator-related pneumonia is costly not only in terms of treatment, equipment, and length of stay but also in terms of patient morbidity and mortality. From October 1995 through March 1996 an increase in ventilator-related pneumonia cases, of which 83% were caused by methicillin-resistant Staphylococcus aureus (MRSA), was noted at a Veterans Affairs medical center. A multidisciplinary team based on the TQI model and using TQI tools, methodology, and principles of problem solving was subsequently formed to look into ventilator-related pneumonia. The team's data collection and analysis efforts identified numerous opportunities for improvement. The primary outcome has been a decrease in the incidence of ventilator-related pneumonia that has resulted in substantial cost savings.

Lower respiratory tract colonization and infection during severe acute respiratory distress syndrome: incidence and diagnosis

Ventilator-associated pneumonia (VAP) is difficult to detect and is often unsuspected during adult respiratory distress syndrome (ARDS). We prospectively evaluated lower respiratory tract (LRT) colonization and infection in 30 patients with severe ARDS (PaO2/FIO2 ratio < 150 mm Hg), using repeated quantitative cultures of plugged telescopic catheter (PTC) specimens taken blindly via the endotracheal tube every 48 to 72 h after onset of ARDS. All patients except one were receiving antibiotics. When VAP was suspected on the presence of clinical criteria for infection, a repeated PTC and, when possible, a bronchoalveolar lavage (BAL) were obtained before any new antimicrobials were administered; samples growing > or = 10(3) cfu/ml (PTC) or > or = 10(4) cfu/ml (BAL) were considered diagnostic of infection. Twenty-four VAP episodes were diagnosed in 18 patients (60% of patients or 4.2/100 ventilator-days) a mean of 9.8+/-5.7 d after onset of ARDS. Eighteen LRT colonization episodes were recorded; 16 of 24 (66%) VAP episodes were preceded (by 2 to 6 d) by LRT colonization with the same organism(s), and only two episodes of colonization were not followed by VAP. We conclude that although VAP is of relatively late-onset during severe ARDS, its incidence is much higher than in other conditions and can be underestimated. Lower airways colonization is consistently followed by infection with the same organisms and precedes VAP in two thirds of episodes. Repeated protected specimens taken blindly may provide a useful means to predict infection and therefore allow early antimicrobial therapy in high-risk patients with diffuse lung injury.

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.

Prophylaxis with enteral antibiotics in ventilated patients: selective decontamination or selective cross-infection?

Selective decontamination of the digestive tract (SDD) has been evaluated as a method to prevent colonization and infection in ventilated patients in 40 trials. On the basis of an assumption that cross-infection would be reduced as a consequence of SDD and that this would distort the results of SDD studies that used concurrent controls, 14 studies used historic controls. To test this assumption, three observations from the two types of studies were compared. (i) The differences between observed and expected event rates for each study were used to perform a meta-analysis. This revealed that the summary odds ratios for bacteremia and respiratory infection were marked by significant heterogeneity (P > 0.95) and inconsistencies between those derived from studies with concurrent versus studies with historic controls. (ii) Where the data were available, the rates of acquisition of colonization in control groups were higher in studies with concurrent controls than in studies with historic controls. (iii) At least four studies with concurrent controls have shown a pattern of pathogenic isolates consistent with cross-infection between groups. These results are contrary to the initial assumption and suggest the possibility that SDD represents a major cross-infection hazard.

Diagnosing ventilator-associated pneumonia: the role of bronchoscopy

OBJECTIVE

To discuss the two diagnostic procedures used most frequently to obtain uncontaminated lower airway secretions during bronchoscopy.

DESIGN

This article reviews the contributing risk factors of ventilator-associated pneumonia (VAP) and the recent studies that have assessed the usefulness of the protected specimen brush (PSB) and bronchoalveolar lavage (BAL) in the nonimmunocompromised host.

RESULTS

A prompt, accurate diagnosis of VAP, including specific identification of the bacterial pathogen, remains a common challenge in the intensive-care unit. Standard clinical criteria are of suboptimal specificity for making decisions, including selecting antibiotic therapy. Bronchoscopic techniques of lung secretion sampling can be used in the intensive-care unit in an effort to overcome the effects of oropharyngeal contamination. The PSB and BAL, used appropriately, can help intensive-care clinicians formulate specific antimicrobial therapy. Evaluation of intracellular bacteria obtained by BAL has been reported to be useful in guiding empiric antibiotic therapy while the final results of cultures obtained with the PSB are pending. Prior antibiotic therapy, however, may confound the interpretation and clinical utility of results.

CONCLUSION

Currently, for a patient taking antibiotic therapy, no reliable technique nor quantitative culture threshold exists to help in diagnosing suspected VAP or in guiding antibiotic therapy. If the clinical situation allows, antibiotic therapy should be discontinued for 48 hours; then, the PSB, BAL, protected BAL, or endobronchial aspiration should be used. These contemporary modalities, however, necessitate further clinical trials before widespread use is warranted.

[Value of the cytology of bronchoalveolar lavage in the early diagnosis of nosocomial lung infections in patients with thoracic injuries]

Mechanically ventilated patients, especially those with thorax trauma, suffer commonly from nosocomial pneumonia. In these patients, conventional diagnostic criteria for bacterial pneumonia may not be completely reliable, as an accurate interpretation of the chest radiograph is too difficult. The invasive means for the diagnosis of pneumonia (protected specimen brush, bronchoalveolar lavage), require 24-48 hours to obtain the results of cultures. Therefore no information is available to guide the initial choice of antimicrobial therapy. For some authors, the quantification of intracellular bacteria, present in cytocentrifuged preparations made from lavage fluid, may provide rapid identification of patients with pneumonia. We evaluated the benefit of this type of analysis in thorax trauma patients. In 36 patients, 48 samples were taken. With a threshold value of 10% of cells containing intracellular organisms, microscopic examination had a sensitivity and a specificity of 83%. We conclude that this technique may be useful for the early diagnosis of nosocomial pneumonia in ventilated thorax trauma patients.