Multidrug-resistant Pseudomonas aeruginosa ventilator-associated pneumonia: the role of endotracheal aspirate surveillance cultures

The threat of multidrug-resistant/extensively drug-resistant Gram-negative respiratory infections: another pandemic

Antibiotic resistance is recognised as a global threat to human health by national healthcare agencies, governments and medical societies, as well as the World Health Organization. Increasing resistance to available antimicrobial agents is of concern for bacterial, fungal, viral and parasitic pathogens. One of the greatest concerns is the continuing escalation of antimicrobial resistance among Gram-negative bacteria resulting in the endemic presence of multidrug-resistant (MDR) and extremely drug-resistant (XDR) pathogens. This concern is heightened by the identification of such MDR/XDR Gram-negative bacteria in water and food sources, as colonisers of the intestine and other locations in both hospitalised patients and individuals in the community, and as agents of all types of infections. Pneumonia and other types of respiratory infections are among the most common infections caused by MDR/XDR Gram-negative bacteria and are associated with high rates of mortality. Future concerns are already heightened due to emergence of resistance to all existing antimicrobial agents developed in the past decade to treat MDR/XDR Gram-negative bacteria and a scarcity of novel agents in the developmental pipeline. This clinical scenario increases the likelihood of a future pandemic caused by MDR/XDR Gram-negative bacteria.

KPC-2 carbapenemase-producing Pseudomonas aeruginosa reaching Germany

Background

Antimicrobial resistance due to carbapenemase expression poses a worldwide threat in healthcare. Inter-genus exchange of genetic information is of utmost importance in this context.

Objectives

Here, to the best of our knowledge, we describe the first detection and characterization of a KPC-2-producing Pseudomonas aeruginosa in Germany.

Methods

Characterization of the isolate was performed using MALDI-TOF MS, automated microdilution and MLST. Carbapenemase detection was performed using phenotypic and genotypic assays. The blaKPC-2-carrying plasmid was transformed into Escherichia coli NEB® 10-beta. The purified plasmid DNA was sequenced using the Illumina technique.

Results

The isolate expressed ST235 and was resistant to carbapenems. Antimicrobial susceptibility testing revealed colistin to be the only antimicrobial agent active in vitro. The blaKPC-2 gene was located on a replicon type lncHI1 plasmid as part of Tn4401.

Conclusions

The first detection (to the best of our knowledge) of plasmid-encoded KPC-2 in P. aeruginosa in Germany may point to a currently underestimated spread of carbapenemases among clinically relevant Gram-negative bacteria. Here, to the best of our knowledge, we also provide the first report of blaKPC-2 associated with the IncHI1 plasmid.

Multi-drug resistant organism infections in a medical ICU: Association to clinical features and impact upon outcome

OBJECTIVE

To define clinical features associated with Intensive Care Unit (ICU) infections caused by multi-drug resistant organisms (MDRO) and their impact on patient outcome.

DESIGN

A single-center, retrospective case-control study was carried out between January 2010 and May 2010.

SETTING

A medical ICU (MICU) in the United States.

PATIENTS

The study included a total of 127 MDRO-positive patients and 186 MDRO-negative patients.

INTERVENTIONS

No interventions were carried out.

RESULTS

Out of a total of 313 patients, MDROs were present in 127 (41.7%). Based on the multivariate analysis, only infection as a cause of admission [OR 3.3 (1.9-5.8)]), total days of ventilation [OR 1.07 (1.01-1.12)], total days in hospital [OR 1.04 (1.01-1.07)], immunosuppression [OR 2.04 (1.2-3.5)], a history of hyperlipidemia [OR 2.2 (1.2-3.8)], surgical history [OR 1.82 (1.05-3.14)] and age [OR 1.02 (1.00-1.04)] were identified as clinical factors independently associated to MDROs, while the Caucasian race was negatively associated to MDROs. The distribution of days on ventilation, days in hospital and days of antibiotic treatment prior to infection differed between the MDRO-positive and MDRO-negative groups. The MDRO-positive patients showed a greater median number of days in hospital and days of antibiotic treatment before infection, with a greater median number of days in hospital, days of antibiotic treatment and days of ventilation after infection, compared to the MDRO-negative patients. The mortality rate was not significantly different between the two groups. Appropriate empirical antibiotic therapy was prescribed in 82% of the MDRO-positive cases - such treatment being started within 24h after onset of the infection in 68.5% of the cases.

CONCLUSION

Defining clinical factors associated with MDRO infections and administering timely and appropriate empirical antibiotic therapy may help reduce the mortality associated with these infections. In our hospital we did not withhold broad spectrum drugs as empirical therapy in patients with clinical features associated to MDRO infection. Our rate of appropriate empirical therapy was therefore high, which could explain the absence of excessive mortality in patients infected with MDROs.

Surveillance cultures in healthcare-associated pneumonia: sense or nonsense?

PURPOSE OF REVIEW

This review explores the usefulness of surveillance cultures in healthcare-associated pneumonia (HCAP).

RECENT FINDINGS

The definition of HCAP is controversial. Causative micro-organisms of HCAP resemble those found in hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP). Some types of surveillance cultures have proven useful in hospitalized patients. Whereas numerous studies have investigated the role of surveillance cultures in VAP, one may wonder whether surveillance culture implementation should belong in HCAP management guidelines.

SUMMARY

Studies exploring the usefulness of obtaining surveillance cultures in VAP are numerous, but are mostly retrospective, observational and/or quasi-experimental in nature. Surveillance cultures may be useful for antibiotic guidance, but positive predictive value and specificity of surveillance cultures are low, obviously negatively impacting on cost effectiveness, especially in the large population at risk for HCAP. On the other hand, multidrug-resistance is increasing and surveillance cultures for methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci in ICU-admitted patients appeared useful and cost-effective. Furthermore, surveillance cultures for the presence of multidrug-resistant Gram-negative bacilli might be useful for antibiotic guidance. Currently, neither community-acquired pneumonia, HCAP, HAP nor VAP guidelines incorporate surveillance cultures. In the future, surveillance cultures in populations at risk for HCAP may be able to differentiate HCAP from other kinds of pneumonia and authorize its reason for existence.

Global prospective epidemiologic and surveillance study of ventilator-associated pneumonia due to Pseudomonas aeruginosa

OBJECTIVE

To estimate the prevalence of ventilator-associated pneumonia caused by Pseudomonas aeruginosa in patients at risk for ventilator-associated pneumonia and to describe risk factors for P. aeruginosa ventilator-associated pneumonia.

DESIGN

Prospective, observational study.

SETTING

ICUs at 56 sites in 11 countries across four regions: the United States (n = 502 patients), Europe (n = 495), Latin America (n = 500), and Asia Pacific (n = 376).

PATIENTS

Adults intubated and mechanically ventilated for 48 hours to 7 days, inclusive.

INTERVENTIONS

None (local standard of care).

MEASUREMENTS AND MAIN RESULTS

Ventilator-associated pneumonia prevalence as defined by local investigators were 15.6% (293/1,873) globally, 13.5% in the United States, 19.4% in Europe, 13.8% in Latin America, and 16.0% in Asia Pacific (p = 0.04). Corresponding P. aeruginosa ventilator-associated pneumonia prevalences were 4.1%, 3.4%, 4.8%, 4.6%, and 3.2% (p = 0.49). Of 50 patients with P. aeruginosa ventilator-associated pneumonia who underwent surveillance testing, 19 (38%) had prior P. aeruginosa colonization and 31 (62%) did not (odds ratio, 7.99; 95% CI, 4.31-14.71). Of predefined risk factors for multidrug resistance (hereafter, risk factors), the most frequent in all patients were antimicrobial therapy within 90 days (51.9% of enrolled patients) and current hospitalization of more than or equal to 5 days (45.3%). None of these risk factors were significantly associated with P. aeruginosa ventilator-associated pneumonia by multivariate logistic regression. Risk factors associated with prior P. aeruginosa colonization were antimicrobial therapy within 90 days (odds ratio, 0.46; 95% CI, 0.29-0.73) and high proportion of antibiotic resistance in the community or hospital unit (odds ratio, 1.79; 95% CI, 1.14-2.82).

CONCLUSIONS

Our findings suggest that ventilator-associated pneumonia remains a common ICU infection and that P. aeruginosa is one of the most common causative pathogens. The odds of developing P. aeruginosa ventilator-associated pneumonia were eight times higher in patients with prior P. aeruginosa colonization than in uncolonized patients, which in turn was associated with local resistance.

Respiratory infections in patients undergoing mechanical ventilation

Lower respiratory tract infections in mechanically ventilated patients are a frequent cause of antibiotic treatment in intensive-care units. These infections present as severe sepsis or septic shock with respiratory dysfunction in intubated patients. Purulent respiratory secretions are needed for diagnosis, but distinguishing between pneumonia and tracheobronchitis is not easy. Both presentations are associated with longlasting mechanical ventilation and extended intensive-care unit stay, providing a rationale for antibiotic treatment initiation. Differentiation of colonisers from true pathogens is difficult, and microbiological data show Staphylococcus aureus and Pseudomonas aeruginosa to be of great concern because of clinical outcomes and therapeutic challenges. Key management issues include identification of the pathogen, choice of initial empirical antibiotic, and decisions with regard to the resolution pattern.

Risk of developing pneumonia is enhanced by the combined traits of fluoroquinolone resistance and type III secretion virulence in respiratory isolates of Pseudomonas aeruginosa

OBJECTIVES

To determine the differential association of host characteristics, antimicrobial resistance, and type III secretion system virulence of Pseudomonas aeruginosa isolates with respiratory syndromes in hospitalized adult patients.

DESIGN

Retrospective, cohort study.

SETTING

Community teaching hospital.

PATIENTS

Two hundred eighteen consecutive adult patients with respiratory culture positive for P. aeruginosa between January 2005 to January 2010.

INTERVENTIONS

Medical charts were reviewed to obtain demographic, laboratory, radiographic, and clinical information. Isolates were assayed by polymerase chain reaction for genes encoding the type III secretion system effectors (ExoU, ExoS, and PcrV) and for strain relatedness using randomly amplified polymorphic DNA analysis. Levofloxacin susceptibility was determined by broth microdilution. Patients were grouped by colonization, bronchitis, or pneumonia and were compared for differential risk of developing the clinical syndrome with respect to host and microbial characteristics.

MEASUREMENTS AND MAIN RESULTS

Half of the study cohort (54%, 117 of 218) had pneumonia, 32% (70 of 218) had bronchitis, and 14% (31 of 218) had colonization; in-hospital mortality was 35%, 11%, and 0%, respectively. Host factors strongly associated with pneumonia development were residence in long-term care facility, healthcare-associated acquisition of P. aeruginosa, higher Acute Physiology and Chronic Health Evaluation II score, presence of enteral feeding tube, mechanical ventilation, and recent history of pneumonia. Fluoroquinolone-resistant (57% vs 34%, 16%; p < 0.0001) and multidrug-resistant (36% vs 26%, 7%; p = 0.0045) strains were more likely to cause pneumonia than bronchitis or colonization, respectively. Analysis of host and microbial factors in a multivariate regression model yielded the combined traits of fluoroquinolone resistance and gene encoding the type III secretion system ExoU effector in P. aeruginosa as the single most significant predictor of pneumonia development.

CONCLUSIONS

These results suggest that fluoroquinolone-resistant phenotype in a type III secretion system exoU strain background contributes toward the pathogenesis of P. aeruginosa in pneumonia.

A systematic review and meta-analyses show that carbapenem use and medical devices are the leading risk factors for carbapenem-resistant Pseudomonas aeruginosa

A systematic review and meta-analyses were performed to identify the risk factors associated with carbapenem-resistant Pseudomonas aeruginosa and to identify sources and reservoirs for the pathogen. A systematic search of PubMed and Embase databases from 1 January 1987 until 27 January 2012 identified 1,662 articles, 53 of which were included in a systematic review and 38 in a random-effects meta-analysis study. The use of carbapenem, use of fluoroquinolones, use of vancomycin, use of other antibiotics, having medical devices, intensive care unit (ICU) admission, having underlying diseases, patient characteristics, and length of hospital stay were significant risk factors in multivariate analyses. The meta-analyses showed that carbapenem use (odds ratio [OR] = 7.09; 95% confidence interval [CI] = 5.43 to 9.25) and medical devices (OR = 5.11; 95% CI = 3.55 to 7.37) generated the highest pooled estimates. Cumulative meta-analyses showed that the pooled estimate of carbapenem use was stable and that the pooled estimate of the risk factor "having medical devices" increased with time. We conclude that our results highlight the importance of antibiotic stewardship and the thoughtful use of medical devices in helping prevent outbreaks of carbapenem-resistant P. aeruginosa.

Is a strategy based on routine endotracheal cultures the best way to prescribe antibiotics in ventilator-associated pneumonia?

OBJECTIVES

The objectives of this study were to evaluate if a strategy based on routine endotracheal aspirate (ETA) cultures is better than using the American Thoracic Society/Infectious Diseases Society of America (ATS/IDSA) guidelines to prescribe antimicrobials in ventilator-associated pneumonia (VAP).

METHODS

This was a prospective, observational, cohort study conducted in a 15-bed ICU and comprising 283 patients who were mechanically ventilated for ≥48 h. Interventions included twice-weekly ETA; BAL culture was done if VAP was suspected. BAL (collected at the time of VAP) plus ETA cultures (collected≤7 days before VAP) (n=146 different pairs) were defined. We compared two models of 10 days of empirical antimicrobials (ETA-based vs ATS/IDSA guidelines-based strategies), analyzing their impact on appropriateness of therapy and total antimicrobial-days, using the BAL result as the standard for comparison.

RESULTS

Complete ETA and BAL culture concordance (identical pathogens or negative result) occurred in 52 pairs; discordance (false positive or false negative) in 67, and partial concordance in two. ETA predicted the etiology in 62.4% of all pairs, in 74.0% of pairs if ETA was performed≤2 days before BAL, and in 46.2% of pairs if ETA was performed 3 to 7 days before BAL (P=.016). Strategies based on the ATS/IDSA guidelines and on ETA results led to appropriate therapy in 97.9% and 77.4% of pairs, respectively (P<.001). The numbers of antimicrobial-days were 1,942 and 1,557 for therapies based on ATS/IDSA guidelines and ETA results, respectively (P<.001).

CONCLUSIONS

The ATS/IDSA guidelines-based approach was more accurate than the ETA-based strategy for prescribing appropriate, initial, empirical antibiotics in VAP, unless a sample was available≤2 days of the onset of VAP. The ETA-based strategy led to fewer days on prescribed antimicrobials.

Management and prevention of ventilator-associated pneumonia caused by multidrug-resistant pathogens

Ventilator-associated pneumonia (VAP) due to multidrug-resistant (MDR) pathogens is a leading healthcare-associated infection in mechanically ventilated patients. The incidence of VAP due to MDR pathogens has increased significantly in the last decade. Risk factors for VAP due to MDR organisms include advanced age, immunosuppression, broad-spectrum antibiotic exposure, increased severity of illness, previous hospitalization or residence in a chronic care facility and prolonged duration of invasive mechanical ventilation. Methicillin-resistant Staphylococcus aureus and several different species of Gram-negative bacteria can cause MDR VAP. Especially difficult Gram-negative bacteria include Pseudomonas aeruginosa, Acinetobacter baumannii, carbapenemase-producing Enterobacteraciae and extended-spectrum β-lactamase producing bacteria. Proper management includes selecting appropriate antibiotics, optimizing dosing and using timely de-escalation based on antiimicrobial sensitivity data. Evidence-based strategies to prevent VAP that incorporate multidisciplinary staff education and collaboration are essential to reduce the burden of this disease and associated healthcare costs.

Value of lower respiratory tract surveillance cultures to predict bacterial pathogens in ventilator-associated pneumonia: systematic review and diagnostic test accuracy meta-analysis

PURPOSE

In ventilator-associated pneumonia (VAP), early appropriate antimicrobial therapy may be hampered by involvement of multidrug-resistant (MDR) pathogens.

METHODS

A systematic review and diagnostic test accuracy meta-analysis were performed to analyse whether lower respiratory tract surveillance cultures accurately predict the causative pathogens of subsequent VAP in adult patients. Selection and assessment of eligibility were performed by three investigators by mutual consideration. Of the 525 studies retrieved, 14 were eligible for inclusion (all in English; published since 1994), accounting for 791 VAP episodes. The following data were collected: study and population characteristics; in- and exclusion criteria; diagnostic criteria for VAP; microbiological workup of surveillance and diagnostic VAP cultures. Sub-analyses were conducted for VAP caused by Staphylococcus aureus, Pseudomonas spp., and Acinetobacter spp., MDR microorganisms, frequency of sampling, and consideration of all versus the most recent surveillance cultures.

RESULTS

The meta-analysis showed a high accuracy of surveillance cultures, with pooled sensitivities up to 0.75 and specificities up to 0.92 in culture-positive VAP. The area under the curve (AUC) of the hierarchical summary receiver-operating characteristic curve demonstrates moderate accuracy (AUC: 0.90) in predicting multidrug resistance. A sampling frequency of >2/week (sensitivity 0.79; specificity 0.96) and consideration of only the most recent surveillance culture (sensitivity 0.78; specificity 0.96) are associated with a higher accuracy of prediction.

CONCLUSIONS

This study provides evidence for the benefit of surveillance cultures in predicting MDR bacterial pathogens in VAP. However, clinical and statistical heterogeneity, limited samples sizes, and bias remain important limitations of this meta-analysis.

Clinical outcomes of Pseudomonas aeruginosa pneumonia in intensive care unit patients

PURPOSE

Our aim was to identify the clinical profile of intensive care unit (ICU) patients with Pseudomonas aeruginosa (PA) pneumonia and the impact on ICU mortality and duration of mechanical ventilation (MV) of multidrug resistance (MDR) in the PA isolate and inadequate initial antibiotic therapy (IIAT).

METHODS

We conducted a retrospective analysis of data prospectively collected in the 18-bed general ICU of a major teaching hospital in Rome, Italy. The study cohort consisted of 110 adult patients with culture-confirmed PA pneumonia consecutively diagnosed in 2008-2010. ICU survivor and nonsurvivor groups were compared to identify factors associated with ICU mortality.

RESULTS

In 42 (38 %) of the 110 cases of PA pneumonia analyzed, the PA isolate was MDR. Fifty-six (50.9 %) of the patients received IIAT, and 49 (44.5 %) died in ICU. In logistic regression analysis, IIAT, diabetes mellitus, higher Simplified Acute Physiology Score (SAPS) II scores, and older age were independently associated with ICU mortality. Among survivors, those who received IIAT or had MDR PA pneumonia had significantly longer median (interquartile ranges, IQR) periods of post-pneumonia onset MV (16.5 [14.5-20] and 15 [12-18] days, respectively) compared with those whose initial therapy was adequate (8 [6-13] days, P < 0.001) and those whose infections were caused by non-MDR PA (10.5 [6.5-13] days, P = 0.01).

CONCLUSIONS

Our findings highlight the importance of IIAT as a risk factor for mortality in ICU patients with PA pneumonia. MDR in the PA isolate, like IIAT, can significantly increase the need for MV.

Implications of endotracheal tube biofilm in ventilator-associated pneumonia response: a state of concept

INTRODUCTION

Biofilm in endotracheal tubes (ETT) of ventilated patients has been suggested to play a role in the development of ventilator-associated pneumonia (VAP). Our purpose was to analyze the formation of ETT biofilm and its implication in the response and relapse of VAP.

METHODS

We performed a prospective, observational study in a medical intensive care unit. Patients mechanically ventilated for more than 24 hours were consecutively included. We obtained surveillance endotracheal aspirates (ETA) twice weekly and, at extubation, ETTs were processed for microbiological assessment and scanning electron microscopy.

RESULTS

Eighty-seven percent of the patients were colonized based on ETA cultures. Biofilm was found in 95% of the ETTs. In 56% of the cases, the same microorganism grew in ETA and biofilm. In both samples the most frequent bacteria isolated were Acinetobacter baumannii and Pseudomonas aeruginosa. Nineteen percent of the patients developed VAP (N = 14), and etiology was predicted by ETA in 100% of the cases. Despite appropriate antibiotic treatment, bacteria involved in VAP were found in biofilm (50%). In this situation, microbial persistence and impaired response to treatment (treatment failure and relapse) were more frequent (100% vs 29%, P = 0.021; 57% vs 14%, P = 0.133).

CONCLUSIONS

Airway bacterial colonization and biofilm formation on ETTs are early and frequent events in ventilated patients. There is microbiological continuity between airway colonization, biofilm formation and VAP development. Biofilm stands as a pathogenic mechanism for microbial persistence, and impaired response to treatment in VAP.

Diagnosis of ventilator-associated respiratory infections (VARI): microbiologic clues for tracheobronchitis (VAT) and pneumonia (VAP)

Intubated patients are at risk of bacterial colonization and ventilator-associated respiratory infection (VARI). VARI includes tracheobronchitis (VAT) or pneumonia (VAP). VAT and VAP caused by multidrug-resistant (MDR) pathogens are increasing in the United States and Europe. In patients with risk factors for MDR pathogens, empiric antibiotics are often initiated for 48 to 72 hours pending the availability of pathogen identification and antibiotic sensitivity data. Extensive data indicate that early, appropriate antibiotic therapy improves outcomes for patients with VAP. Recognizing and treating VARI may allow earlier appropriate therapy and improved patient outcomes.

Inhaled antibiotic therapy for ventilator-associated tracheobronchitis and ventilator-associated pneumonia: an update

Ventilator-associated pneumonia (VAP) remains a leading cause of morbidity and mortality in mechanically-ventilated patients in the Intensive Care Unit (ICU). Ventilator-associated tracheobronchitis (VAT) was previously believed to be an intermediate stage between colonization of the lower respiratory tract and VAP. More recent data, however, suggest that VAT may be a separate entity that increases morbidity and mortality, independently of the occurrence of VAP. Some, but not all, patients with VAT progress to develop VAP. Although inhaled antibiotics alone could be effective for the treatment of VAP, the current consensus of opinion favors their role as adjuncts to systemic antimicrobial therapy for VAP. Inhaled antibiotics are increasingly employed for salvage therapy in patients with VAP due to multi-drug resistant Gram-negative bacteria. In contrast to VAP, VAT could be effectively treated with inhaled antibiotic therapy alone or in combination with systemic antimicrobials.

Differences in biofilm formation and antimicrobial resistance of Pseudomonas aeruginosa isolated from airways of mechanically ventilated patients and cystic fibrosis patients

Pseudomonas aeruginosa biofilms exhibit increased antimicrobial resistance compared with planktonic isolates and are implicated in the pathogenesis of both acute and chronic lung infections. Whilst antibiotic choices for both infections are based on planktonic antibiotic susceptibility results, differences in biofilm-forming ability between the two diseases have not previously been explored. The aim of this study was to compare differences in biofilm formation and antibiotic resistance of P. aeruginosa isolated from intubated patients and from patients with chronic pulmonary disease associated with cystic fibrosis (CF). The temporal evolution of antibiotic resistance in clonal P. aeruginosa strains isolated from CF patients during periods of chronic infection and acute pulmonary exacerbation was also evaluated. Biofilm formation and biofilm antibiotic susceptibilities were determined using a modified microtitre plate assay and were compared with antibiotic susceptibility results obtained using traditional planktonic culture. Clonality was confirmed using random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) analysis. Pseudomonas aeruginosa isolates collected from intubated patients produced substantially more biofilms compared with CF isolates. There was considerable heterogeneity in biofilm-forming ability amongst the CF isolates and this was unrelated to pulmonary status. Biofilm antibiotic resistance developed rapidly amongst clonal CF isolates over time, whilst traditional antibiotic resistance determined using planktonic cultures remained stable. There was a significant positive correlation between imipenem/cilastatin and ceftazidime resistance and biofilm-forming ability. The variability in biofilm-forming ability in P. aeruginosa and the rapid evolution of biofilm resistance may require consideration when choosing antibiotic therapy for newly intubated patients and CF patients.