Towards invasive diagnostic techniques as standard management of ventilator-associated pneumonia

Ventilator-Associated Pneumonia at a Tertiary-Care Center in a Developing Country: Incidence, Microbiology, and Susceptibility Patterns of Isolated Microorganisms

Objective:

Ventilator-associated pneumonia (VAP) complicates the course of up to 24% of intubated patients. Data from the Middle East are scarce. The objective of this study was to evaluate the incidence, microbiology, and antimicrobial susceptibility patterns of isolated microorganisms in VAP in a developing country.

Design:

Prospective observational cohort study.

Setting:

The American University of Beirut Medical Center, a tertiary-care center that serves as a major referral center for Lebanon and neighboring countries.

Patients:

All patients admitted to the intensive care and respiratory care units from March to September 2001, and who had been receiving mechanical ventilation for at least 48 hours, were included in the study. Results of samples submitted for culture were recorded and antimicrobial susceptibility testing of isolated pathogens was performed.

Results:

Seventy patients were entered into the study. The incidence of VAP was 47%. Gram-negative bacilli accounted for 83% of all isolates. The most commonly identified organism was Acinetobacter anitratus, followed by Pseudomonas aeruginosa. Fifty percent of all gram-negative bacterial isolates were classified as antibiotic resistant. Compared with patients without VAP, patients with VAP remained intubated for a longer period and stayed in the intensive care unit longer. VAP was not associated with an increased mortality rate.

Conclusion:

Compared with other studies, the results from this referral center in Lebanon indicate a higher incidence of VAP and a high prevalence of resistant organisms. These data are relevant because they direct the choice of empiric antibiotic therapy for VAP.

Impact of Ventilator-Associated Pneumonia on Resource Utilization and Patient Outcome

Objective:

To assess the effect of ventilator-associated pneumonia on resource utilization, morbidity, and mortality.

Design:

Retrospective matched cohort study based on prospectively collected data.

Setting:

Medical intensive care unit of a university teaching hospital.

Patients:

Case-patients were all patients receiving mechanical ventilation for 48 hours or more who experienced an episode of ventilator-associated pneumonia. Control-patients were matched for number of discharge diagnoses, duration of mechanical support before the onset of pneumonia among case-patients, age, admission diagnosis, gender, and study period.

Results:

One hundred six cases of ventilator-associated pneumonia were identified in 452 patients receiving mechanical ventilation. The matching procedure selected 97 pairs. Length of stay in the intensive care unit and duration of mechanical ventilation were greater among case-patients by a mean of 7.2 days (P< .001) and 5.1 days (P< .001), respectively. Median costs were $24,727 (interquartile range, $18,348 to $39,703) among case-patients and $17,438 (interquartile range, $12,261 to $24,226) among control-patients (P< .001). The attributable mortality rate was 7.3% (P = .26). The attributable extra hospital stay was 10 days with an extra cost of $15,986 per episode of pneumonia.

Conclusion:

Ventilator-associated pneumonia negatively affects patient outcome and represents a significant burden on intensive care unit and hospital resources.

A randomized trial of diagnostic techniques for ventilator-associated pneumonia

BACKGROUND

Critically ill patients who require mechanical ventilation are at risk for ventilator-associated pneumonia. Current data are conflicting as to the optimal diagnostic approach in patients who have suspected ventilator-associated pneumonia.

METHODS

In a multicenter trial, we randomly assigned immunocompetent adults who were receiving mechanical ventilation and who had suspected ventilator-associated pneumonia after 4 days in the intensive care unit (ICU) to undergo either bronchoalveolar lavage with quantitative culture of the bronchoalveolar-lavage fluid or endotracheal aspiration with nonquantitative culture of the aspirate. Patients known to be colonized or infected with pseudomonas species or methicillin-resistant Staphylococcus aureus were excluded. Empirical antibiotic therapy was initiated in all patients until culture results were available, at which point a protocol of targeted therapy was used for discontinuing or reducing the dose or number of antibiotics, or for resuming antibiotic therapy to treat a preenrollment condition if the culture was negative.

RESULTS

We enrolled 740 patients in 28 ICUs in Canada and the United States. There was no significant difference in the primary outcome (28-day mortality rate) between the bronchoalveolar-lavage group and the endotracheal-aspiration group (18.9% and 18.4%, respectively; P=0.94). The bronchoalveolar-lavage group and the endotracheal-aspiration group also had similar rates of targeted therapy (74.2% and 74.6%, respectively; P=0.90), days alive without antibiotics (10.4+/-7.5 and 10.6+/-7.9, P=0.86), and maximum organ-dysfunction scores (mean [+/-SD], 8.3+/-3.6 and 8.6+/-4.0; P=0.26). The two groups did not differ significantly in the length of stay in the ICU or hospital.

CONCLUSIONS

Two diagnostic strategies for ventilator-associated pneumonia--bronchoalveolar lavage with quantitative culture of the bronchoalveolar-lavage fluid and endotracheal aspiration with nonquantitative culture of the aspirate--are associated with similar clinical outcomes and similar overall use of antibiotics. (Current Controlled Trials number, ISRCTN51767272 [controlled-trials.com].).

Validation of a rapid diagnostic strategy for determination of significant bacterial counts in bronchoalveolar lavage samples

CONTEXT

Bacterial cultures of bronchoscopic samples require 1 to 2 days for results to be available for use in clinical decisions. We developed a rapid diagnostic testing strategy that is highly sensitive for screening bacteria in bronchoalveolar lavage (BAL) samples, with results available within hours of collection.

OBJECTIVE

To validate the ability of a bacterial adenosine triphosphate (ATP) assay and routine Gram stain microscopy to detect significant bacterial counts in BAL samples.

DESIGN

Four hundred seventy-seven BAL samples from 319 patients suspected of having pneumonia were tested using a rapid diagnostic strategy, consisting of Gram stain and a bacterial ATP assay. Rapid results were compared with quantitative cultures with a positive cutoff of 10(4) CFU/mL or higher.

RESULTS

Significant bacterial counts were identified in 107 samples (22%). The most common etiologic agents were Staphylococcus aureus (25%), Haemophilus influenzae (17%), and Streptococcus pneumoniae (12%). The rapid test results were false negative in 5 cases (S aureus in 2, both Klebsiella pneumoniae and S aureus in 1, and Stenotrophomonas maltophilia and S pneumoniae in 1 case each). The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of the rapid diagnostic strategy were 95.3%, 54.9%, 37.9%, 97.6%, and 63.9%, respectively.

CONCLUSION

A negative result with this rapid diagnostic testing strategy rules out significant bacterial counts in BAL samples with a high degree of certainty and may allow use of narrow-spectrum antimicrobial agents or withholding of empiric antimicrobial therapy in patients suspected of having ventilator-associated pneumonia.

Effect of hospitalization and antimicrobial therapy on antimicrobial resistance of colonizing Staphylococcus epidermidis

Endogenous infections with multi-resistant S. epidermidis are among the leading causes of nosocomial infections. The effect of hospitalization and antimicrobial therapy on antimicrobial resistance of colonizing staphylococci was determined from swabs of the nose, hand, axilla and groin from 157 patients on one day. Hospitalization for >72 hours, compared with <72 hours, was associated with a higher percentage of isolates resistant to oxacillin (56% versus 19%), gentamicin (40% versus 15%), trimethoprim (36% versus 17%), clindamycin (56% versus 17%), and fusidic acid (20% versus 4%; p < 0.01 for all), but not to rifampicin (6% versus 1%) or fosfomycin (43% versus 34%, p > 0.05 for both). Concurrent antimicrobial therapy resulted in increased resistance to oxacillin (61% versus 28%), gentamicin (43% versus 20%), and clindamycin (60% versus 26%; p < 0.01 for all), but not to trimethoprim (39% versus 23%), fusidic acid (19% versus 9%), rifampicin (6% versus 3%), or fosfomycin (46% versus 38%, p > 0.05 for all). The increase in resistant isolates was not independent, since hospitalization and antimicrobial therapy were correlated (p < 0.001). After adjustment for potential risk factors such as diabetes mellitus, central venous catheters, and hemodialysis, the odds ratio for oxacillin resistance was 2.8-3.6. None of the risk factors showed statistically significant results, except for the presence of neoplastic disease, which had a significant interaction (P=0.035). The within-subgroup odds ratios for patients with and without neoplasm were 4.2 (95% CI, 2.3-5.7) and 2.1 (95% CI, 0.78-3.12), respectively. These results show that hospitalization for more than three days, with or without antimicrobial therapy, and the presence of neoplastic disease are associated with increased antimicrobial resistance in colonizing S. epidermidis.

Evaluation of a rapid bacterial ATP assay for screening BAL samples from ICU patients submitted for quantitative bacterial cultures

A novel application of a rapid diagnostic technique for the detection of significant bacterial pathogens (>/=10(4) cfu/mL) in bronchoalveolar lavage (BAL) samples from critically ill ventilated patients is described. This rapid diagnostic assay (UTIscreen, Coral Biotechnology, San Diego, CA) utilizes a luciferin-luciferase reaction to detect bacterial adenosine triphosphate (ATP) and is currently commercially available for screening bacteriuria in urine specimens. One hundred and twenty-eight BAL samples were examined microscopically with Gram's stain and tested in parallel using the bacterial ATP assay and standard quantitative culture. The sensitivity (Sn), specificity (Sp), positive predictive value (PPV), and negative predictive value (NPV) for the detection of bacteria >/=10(4) cfu/ml in BAL specimens for the bacterial ATP assay was 87%, 59%, 39%, and 94%, and for the Gram's stain was 73%, 65%, 39%, and 89%, respectively. The diagnostic utility was improved by combining the results of Gram's stain/bacterial ATP assay results with Sn, Sp, PPV, and NPV of 97%, 38%, 32%, and 97% respectively. A combined negative rapid test consisting of Gram's stain/bacterial ATP assay rules out significant bacteria in BAL samples with a high degree of certainty. Future studies are needed to clinically validate these observations.

Nonantibibiotic measures for the prevention of Gram-positive infections

While Gram-negative bacteria remain a leading cause of nosocomial infections such as ventilator-associated pneumonia and catheter-associated urinary tract infections, Gram-positive cocci are now responsible for a large majority of surgical site and bloodstream infections. A shift has occurred during the last decade and multidrug-resistant micro-organisms have become predominant in most referral centers. Severe infections with Gram-positive micro-organisms such as methicillin-resistant Staphylococcus aureus, coagulase-negative staphylococci, vancomycin-resistant enterococci, penicillin-resistant Streptococcus pneumoniae and, more recently, glycopeptide intermediate S. aureus are now regularly reported to be associated with increased morbidity and represent a true health problem in many institutions. The importance of nonantimicrobial measures to prevent infections and further spread is reviewed in this paper. New evidence of the effectiveness of basic infection control measures that have been regarded of little importance during the last two decades by the exponential progress of technologically sophisticated medicine, is discussed.

Ventilator-associated pneumonia

Ventilator-associated pneumonia (VAP) continues to complicate the course of 8 to 28% of patients receiving mechanical ventilation (MV). In contrast to infections of more frequently involved organs (e.g., urinary tract and skin), for which mortality is low, ranging from 1 to 4%, the mortality rate for VAP ranges from 24 to 50% and can reach 76% in some specific settings or when lung infection is caused by high-risk pathogens. The predominant organisms responsible for infection are Staphylococcus aureus, Pseudomonas aeruginosa, and Enterobacteriaceae, but etiologic agents widely differ according to the population of patients in an intensive care unit, duration of hospital stay, and prior antimicrobial therapy. Because appropriate antimicrobial treatment of patients with VAP significantly improves outcome, more rapid identification of infected patients and accurate selection of antimicrobial agents represent important clinical goals. Our personal bias is that using bronchoscopic techniques to obtain protected brush and bronchoalveolar lavage specimens from the affected area in the lung permits physicians to devise a therapeutic strategy that is superior to one based only on clinical evaluation. When fiberoptic bronchoscopy is not available to physicians treating patients clinically suspected of having VAP, we recommend using either a simplified nonbronchoscopic diagnostic procedure or following a strategy in which decisions regarding antibiotic therapy are based on a clinical score constructed from seven variables. Selection of the initial antimicrobial therapy should be based on predominant flora responsible for VAP at each institution, clinical setting, information provided by direct examination of pulmonary secretions, and intrinsic antibacterial activities of antimicrobial agents and their pharmacokinetic characteristics. Further trials will be needed to clarify the optimal duration of treatment and the circumstances in which monotherapy can be safely used.

Prevention and management of ventilator-associated pneumonia

Worldwide, the increasing rates of microbial resistance represent a serious public health problem. Therefore, measures to prevent ventilator-associated pneumonia gain increasing importance. Because antimicrobial treatment in the ICU is a major source of microbial resistance, prevention should be understood not only as the sum of preventive measures but also as part of any management strategy. In this year of review, several important contributions have been made to a better understanding of the relative role of preventive measures. This is particularly true of noninvasive ventilation, continuous aspiration of subglottic secretions, and closed endotracheal suctioning. Management strategies for ventilator-assisted pneumonia remain highly controversial. Despite two decades of vigorous research, there is still no evidence that invasive bronchoscopic techniques should form part of a routine approach to suspected ventilator-assisted pneumonia. Moreover, an impact in terms of important outcome variables could not be consistently demonstrated. In the authors' view, the controversy regarding the relative validity of diagnostic tools should end, and the focus should shift to strategies that define low-risk patients with suspected ventilator-assisted pneumonia who can safely be treated by short-term monotherapy. Finally, several contributions have refined the established treatment regimen. Several new drugs for the treatment of ventilator-assisted pneumonia caused by Gram-positive multiresistant pathogens have been evaluated with promising results.

Infection control in the ICU

Nosocomial infections (NIs) now concern 5 to 15% of hospitalized patients and can lead to complications in 25 to 33% of those patients admitted to ICUs. The most common causes are pneumonia related to mechanical ventilation, intra-abdominal infections following trauma or surgery, and bacteremia derived from intravascular devices. This overview is targeted at ICU physicians to convince them that the principles of infection control in the ICU are based on simple concepts and that the application of preventive strategies should not be viewed as an administrative or constraining control of their activity but, rather, as basic measures that are easy to implement at the bedside. A detailed knowledge of the epidemiology, based on adequate surveillance methodologies, is necessary to understand the pathophysiology and the rationale of preventive strategies that have been demonstrated to be effective. The principles of general preventive measures such as the implementation of standard and isolation precautions, and the control of antibiotic use are reviewed. Specific practical measures, targeted at the practical prevention and control of ventilator-associated pneumonia, sinusitis, and bloodstream, urinary tract, and surgical site infections are detailed. Recent data strongly confirm that these strategies may only be effective over prolonged periods if they can be integrated into the behavior of all staff members who are involved in patient care. Accordingly, infection control measures are to be viewed as a priority and have to be integrated fully into the continuous process of improvement of the quality of care.

Colonization and infection by Serratia species in a paediatric surgical intensive care unit

Serratia species are known for the infections they cause in adult and neonatal intensive care patients. Little is known about colonization and infection in paediatric intensive care patients. This study aims to describe the type of infections in critically ill newborns, infants and children, caused by Serratia spp., to compare patients colonized by Serratia spp. to patients colonized with other micro-organisms, and to assess the importance of the respiratory and digestive tracts as reservoirs. To this end, all microbiological samples taken from patients in our paediatric surgical intensive care unit between January 1986 and November 1993 were retrieved from the hospital database and patient records reviewed. Serratia spp. were isolated 1356 times from 97 patients. Eighty-five infections were diagnosed in 40 patients. Infections of the respiratory tract occurred most frequently (n= 65), followed by septicaemia (13), urinary tract infections (3), omphalitis (2), meningitis (1) and conjunctivitis (1). Colonization by Serratia spp. was associated with yearly age at admission, long ICU stay and high mortality. Both the respiratory and digestive tracts were frequently colonized. Our findings do not support the contention that the digestive tract is more important as reservoir than the respiratory tract in neonates.