Bacteremic nosocomial pneumonia. A 7-year experience in one institution

Evaluation of immune and pyroptosis status in a model of sepsis-induced secondary pneumonia

In recent years, researchers have focused on studying the mechanism of sepsis-induced immunosuppression, but there is still a lack of suitable animal models that accurately reflect the process of sepsis-induced immunosuppression. The aim of this study was to evaluate the immune status at various stages in a model of sepsis-induced secondary pneumonia and to demonstrate whether pyroptosis is one of the modes of immune cell death in sepsis. Firstly, we established a sepsis model in C57BL/6J mice using cecal ligation and puncture (CLP). The surviving mice were treated with a 40 μL suspension of P.aeruginosa (Pa) under anesthesia on day 4 post-CLP to establish a sepsis-induced secondary pneumonia model. Secondly, routine blood tests, serum ALT and PCT levels, gross lung specimens, and H&E staining of the lung and liver tissues were used to assess the successful establishment of this model. Serum levels of TNF-α and IL-6, the CD4+/CD8+ratio in blood, H&E staining of the spleen, and immunohistochemistry of CD4 and CD8 in the spleen were detected to evaluate the immune status of the model mice. Finally, the expression levels of pyroptosis-related proteins in the spleen were detected by Western blot. The expression of GSDMD was assessed using immunohistochemistry, and pyroptosis was directly observed through transmission electron microscopy. The experimental results above confirmed the successful construction of the model for sepsis-induced secondary pneumonia, demonstrating its ability to reflect sepsis-induced immunosuppression. Moreover, the expression of pyroptosis-related proteins, immunohistochemical GSDMD, and transmission electron microscopy of the spleen showed that pyroptosis was one of the modes of immune cell death in sepsis.

Comparative study of the etiology of nosocomial bacteremic pneumonia in ventilated and non-ventilated patients: a 10-year experience in an institution

IMPORTANCE

This study on bacteremic nosocomial pneumonia (bNP) demonstrates the importance of this condition both in patients undergoing and not undergoing mechanical ventilation. Staphylococcus aureus, Enterobacterales, and non-fermenting Gram-negative bacilli are all causative agents in ventilator-associated pneumonia (VAP) and hospital-acquired pneumonia (HAP), with a predominance of S. aureus in HAP and of Pseudomonas aeruginosa in VAP. Mortality in this condition is very high. Therefore, new therapeutic and preventive approaches should be sought.

The effect of artesunate to reverse CLP-induced sepsis immunosuppression mice with secondary infection is tightly related to reducing the apoptosis of T cells via decreasing the inhibiting receptors and activating MAPK/ERK pathway

T cells play an important role in regulating immune system balance. Sepsis-associated immunosuppression causes apoptosis of T cells and a decrease in their number. Previously, artesunate was found to have an immunomodulatory effect on immunosuppression in model mice with cecal ligation and puncture (CLP)-induced sepsis. In the present study, mouse sepsis models of CLP and CLP with secondary infection were established and treated with artesunate in order to examine the effect of artesunate on adaptive immune response in sepsis-related immunosuppression. The results showed that artesunate treatment could increase the survival rate of CLP mice with secondary Pseudomonas aeruginosa infection, increase the bacterial clearance rate, and also increase the level of the pro-inflammatory cytokine TNF-α. In addition, artesunate resulted in an increase in the number of T cells, CD4+ T cells and CD8+ T cells, and inhibited CD4+ and CD8+ T-cell apoptosis. Artesunate was also found to inhibit the expression of the inhibitory receptors of PD-1, CTLA-4, and BTLA, but it did not affect the expression of Tim-3. Additionally, artesunate significantly increased the phosphorylated ERK level of CD4+ T cells and CD8+ T cells and inhibited mitochondrial pathway-mediated apoptosis in CLP mice with Pseudomonas aeruginosa infection. These findings reveal that artesunate has an immunomodulatory effect on the adaptive immune response in sepsis. These effects include an increase in the numbers of T cells, CD4+ T cells, and CD8+ T cells through inhibition of the expression of inhibitory receptors and promotion of the MAPK/ERK pathway.

Mechanisms and Targeted Therapies for Pseudomonas aeruginosa Lung Infection

Pseudomonas aeruginosa is a complex gram-negative facultative anaerobe replete with a variety of arsenals to activate, modify, and destroy host defense mechanisms. The microbe is a common cause of nosocomial infections and an antibiotic-resistant priority pathogen. In the lung, P. aeruginosa disrupts upper and lower airway homeostasis by damaging the epithelium and evading innate and adaptive immune responses. The biology of these interactions is essential to understand P. aeruginosa pathogenesis. P. aeruginosa interacts directly with host cells via flagella, pili, lipoproteins, lipopolysaccharides, and the type III secretion system localized in the outer membrane. P. aeruginosa quorum-sensing molecules regulate the release of soluble factors that enhance the spread of infection. These characteristics of P. aeruginosa differentially affect lung epithelial, innate, and adaptive immune cells involved in the production of mediators and the recruitment of additional immune cell subsets. Pathogen interactions with individual host cells and in the context of host acute lung infection are discussed to reveal pathways that may be targeted therapeutically.

Mice Survival and Plasmatic Cytokine Secretion in a "Two Hit" Model of Sepsis Depend on Intratracheal Pseudomonas Aeruginosa Bacterial Load

Sepsis is characterized by pro- and anti-inflammatory responses following infection. While inflammation is responsible for widespread organ damage, anti-inflammatory mediators lead to immunoparalysis increasing susceptibility to secondary infections (nosocomial pneumonia). We aimed to investigate the impact of bacterial load on survival and cytokine release in a two-hit murine (C57BL/6J) model of CLP followed by P. aeruginosa pneumonia. Plasmatic TNFα, IL-6, IL-10, sTNFr I and II were quantified until 13 days. At D5, splenocytes were processed for immunological assays or mice were intratracheally instilled with Pseudomonas aeruginosa (5.10⁶, 2.10⁷ and 10⁸ CFU) to evaluate survival and cytokines production. TNFα, sTNFrs, IL-6 and IL-10 increased 2h post CLP. TNFα and sTNFrs declined respectively one and two days later. In CLP mice, IL-6 and IL-10 remained high for the whole experiment, as compared to Sham. At D5, for CLP mice, whereas total T cells population (CD3+) decreased, Treg fraction (CD4+/CD25+) increased. In parallel, T cells proliferation and LPS-stimulated splenocytes ability to release TNFα decreased. At D13, survival was 100% after 5.10⁶ CFU, 50% for CLP mice after 2.10⁷ CFU and 0% for CLP and Sham after 10⁸ CFU. After instillation, IL-10 and IL-6 increased and appeared to be dose and time dependent. Pseudomonas was detected in all CLP and Sham’s lungs; in spleen and liver only in CLP at 2.10⁷ CFU, and in CLP and Sham at 10⁸ CFU. We demonstrated that post-CLP immunosuppression followed by Pseudomonas aeruginosa lung instillation increases mortality reactivates cytokines secretion and is associated with systemic dissemination in septic mice depending on bacterial load.

A cohort study of bacteremic pneumonia: The importance of antibiotic resistance and appropriate initial therapy?

Bacteremic pneumonia is usually associated with greater mortality. However, risk factors associated with hospital mortality in bacteremic pneumonia are inadequately described.The study was a retrospective cohort study, conducted in Barnes-Jewish Hospital (2008-2015). For purposes of this investigation, antibiotic susceptibility was determined according to ceftriaxone susceptibility, as ceftriaxone represents the antimicrobial agent most frequently recommended for hospitalized patients with community-acquired pneumonia as opposed to nosocomial pneumonia. Two multivariable analyses were planned: the first model included resistance to ceftriaxone as a variable, whereas the second model included the various antibiotic-resistant species (methicillin-resistant Staphylococcus aureus, Pseudomonas aeruginosa, and Enterobacteriaceae).In all, 1031 consecutive patients with bacteremic pneumonia (mortality 37.1%) were included. The most common pathogens associated with infection were S aureus (34.1%; methicillin resistance 54.0%), Enterobacteriaceae (28.0%), P aeruginosa (10.6%), anaerobic bacteria (7.3%), and Streptococcus pneumoniae (5.6%). Compared with ceftriaxone-susceptible pathogens (46.8%), ceftriaxone-resistant pathogens (53.2%) were significantly more likely to receive inappropriate initial antibiotic treatment (IIAT) (27.9% vs 7.1%; P < 0.001) and to die during hospitalization (41.5% vs 32.0%; P = 0.001). The first logistic regression analysis identified IIAT with the greatest odds ratio (OR) for mortality (OR 2.2, 95% confidence interval [CI] 1.5-3.2, P < 0.001). Other independent predictors of mortality included age, mechanical ventilation, immune suppression, prior hospitalization, prior antibiotic administration, septic shock, comorbid conditions, and severity of illness. In the second multivariable analysis that included the antibiotic-resistant species, IIAT was still associated with excess mortality, and P aeruginosa infection was identified as an independent predictor of mortality (OR 1.6, 95% CI 1.1-2.2, P = 0.047), whereas infection with ceftriaxone-resistant Enterobacteriaceae (OR 0.6, 95% CI 0.4-1.0, P = 0.050) was associated with lower mortality.More than one-third of our patients hospitalized with bacteremic pneumonia died. IIAT was identified as the most important risk factor for hospital mortality and the only risk factor amenable to potential intervention. Specific antibiotic-resistant pathogen species were also associated with mortality.

Risk factors for hospital-acquired pneumonia outside the intensive care unit: a case-control study

BACKGROUND

Hospital-acquired pneumonia (HAP) is one of the leading nosocomial infections and is associated with high morbidity and mortality. Numerous studies on HAP have been performed in intensive care units (ICUs), whereas very few have focused on patients in general wards. This study examined the incidence of, risk factors for, and outcomes of HAP outside the ICU.

METHODS

An incident case-control study was conducted in a 600-bed hospital between January 2006 and April 2008. Each case of HAP was randomly matched with 2 paired controls. Data on risk factors, patient characteristics, and outcomes were collected.

RESULTS

The study group comprised 119 patients with HAP and 238 controls. The incidence of HAP outside the ICU was 2.45 cases per 1,000 discharges. Multivariate analysis identified malnutrition, chronic renal failure, anemia, depression of consciousness, Charlson comorbidity index ≥3, previous hospitalization, and thoracic surgery as significant risk factors for HAP. Complications occurred in 57.1% patients. The mortality attributed to HAP was 27.7%.

CONCLUSIONS

HAP outside the ICU prevailed in patients with malnutrition, chronic renal failure, anemia, depression of consciousness, comorbidity, recent hospitalization, and thoracic surgery. HAP in general wards carries an elevated morbidity and mortality and is associated with increased length of hospital stay and increased rate of discharge to a skilled nursing facility.

Clinical practice guidelines for hospital-acquired pneumonia and ventilator-associated pneumonia in adults

Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) are important causes of morbidity and mortality, with mortality rates approaching 62%. HAP and VAP are the second most common cause of nosocomial infection overall, but are the most common cause documented in the intensive care unit setting. In addition, HAP and VAP produce the highest mortality associated with nosocomial infection. As a result, evidence-based guidelines were prepared detailing the epidemiology, microbial etiology, risk factors and clinical manifestations of HAP and VAP. Furthermore, an approach based on the available data, expert opinion and current practice for the provision of care within the Canadian health care system was used to determine risk stratification schemas to enable appropriate diagnosis, antimicrobial management and nonantimicrobial management of HAP and VAP. Finally, prevention and risk-reduction strategies to reduce the risk of acquiring these infections were collated. Future initiatives to enhance more rapid diagnosis and to effect better treatment for resistant pathogens are necessary to reduce morbidity and improve survival.

Bacteremia is an independent risk factor for mortality in nosocomial pneumonia: a prospective and observational multicenter study

Introduction

Since positive blood cultures are uncommon in patients with nosocomial pneumonia (NP), the responsible pathogens are usually isolated from respiratory samples. Studies on bacteremia associated with hospital-acquired pneumonia (HAP) have reported fatality rates of up to 50%. The purpose of the study is to compare risk factors, pathogens and outcomes between bacteremic nosocomial pneumonia (B-NP) and nonbacteremic nosocomial pneumonia (NB-NP) episodes.

Methods

This is a prospective, observational and multicenter study (27 intensive care units in nine European countries). Consecutive patients requiring invasive mechanical ventilation for an admission diagnosis of pneumonia or on mechanical ventilation for > 48 hours irrespective of admission diagnosis were recruited.

Results

A total of 2,436 patients were evaluated; 689 intubated patients presented with NP, 224 of them developed HAP and 465 developed ventilation-acquired pneumonia. Blood samples were extracted in 479 (69.5%) patients, 70 (14.6%) being positive. B-NP patients had higher Simplified Acute Physiology Score (SAPS) II score (51.5 ± 19.8 vs. 46.6 ± 17.5, P = 0.03) and were more frequently medical patients (77.1% vs. 60.4%, P = 0.01). Mortality in the intensive care unit was higher in B-NP patients compared with NB-NP patients (57.1% vs. 33%, P < 0.001). B-NP patients had a more prolonged mean intensive care unit length of stay after pneumonia onset than NB-NP patients (28.5 ± 30.6 vs. 20.5 ± 17.1 days, P = 0.03). Logistic regression analysis confirmed that medical patients (odds ratio (OR) = 5.72, 95% confidence interval (CI) = 1.93 to 16.99, P = 0.002), methicillin-resistant Staphylococcus aureus (MRSA) etiology (OR = 3.42, 95% CI = 1.57 to 5.81, P = 0.01), Acinetobacter baumannii etiology (OR = 4.78, 95% CI = 2.46 to 9.29, P < 0.001) and days of mechanical ventilation (OR = 1.02, 95% CI = 1.01 to 1.03, P < 0.001) were independently associated with B-NP episodes. Bacteremia (OR = 2.01, 95% CI = 1.22 to 3.55, P = 0.008), diagnostic category (medical patients (OR = 3.71, 95% CI = 2.01 to 6.95, P = 0.02) and surgical patients (OR = 2.32, 95% CI = 1.10 to 4.97, P = 0.03)) and higher SAPS II score (OR = 1.02, 95% CI = 1.01 to 1.03, P = 0.008) were independent risk factors for mortality.

Conclusions

B-NP episodes are more frequent in patients with medical admission, MRSA and A. baumannii etiology and prolonged mechanical ventilation, and are independently associated with higher mortality rates.

A New Approach to Ventilator-associated Pneumonia Based on the PIRO System

Several new scoring systems have been developed over recent years to assess the degree of organ failure (e.g., Acute Physiology and Chronic Health Evaluation [APACHE] II, APACHE III, Sequential Organ Failure Assessment [SOFA], Simplified Acute Physiology Score [SAPS] II, and Multiple Organ Dysfunction Score [MODS]). Most of these were models generated based on the concepts of sepsis, severe sepsis and septic shock. In 2001, an International Sepsis Definition Conference updated these terms in order to facilitate standardized enrolment into clinical trials, but due to their simplicity and easy use physicians rapidly adopted them for daily clinical practice [1].

Infectious background of febrile advanced lung cancer patients who received chemotherapy

The study aimed to determine the diagnostic utility of procalcitonin (PCT) in order to discriminate between infective fever and fever due to inflammation in febrile advanced lung cancer patients treated with cytotoxic chemotherapy. A total of 121 patients with advanced lung cancer, treated with a cytotoxic chemotherapy regimen between September 2007 and September 2008 at Kyoto University Hospital, were recruited. Blood samples were obtained on the first day of the fever. Serum c-reactive protein (CRP) and PCT levels were measured. At least two blood cultures were performed, and sputum was taken for Gram staining and culture. There were 71 episodes in 61 patients in the 12 months of the study, representing 50.4% of our study population. A total of 41 patients (57.7%) were diagnosed with pneumonia using imaging modalities, 6 (8.5%) with bacteremia using blood culture and 4 (5.6%) with urinary tract infections using urine culture. Among the 41 pneumonia cases, culture from sputum revealed pathologic bacteria in 21 (51.2%) and fungal disease in 14 (34.1%) cases. Among the 71 febrile episodes, serum procalcitonin and CRP were measured in 50 episodes. Serum procalcitonin-positive patients showed poor outcomes on antibiotics therapy (Fisher's exact test, p=0.042). Furthermore, serum procalcitonin positivity was able to discriminate infective fever from fever due to inflammation (Chi-square test, p=0.001). We showed the causative organisms of febrile advanced lung cancer patients who received cytotoxic chemotherapy, as well as the possibility of PCT to discriminate infective fever from fever due to inflammation.

Long term trends in the occurrence of nosocomial blood stream infection

OBJECTIVE

To determine trends in the occurrence of nosocomial blood stream infection at the University of Alberta Hospital.

METHODS

A prospective survey of nosocomial blood stream infection was conducted; cases from August 1986 to December 1996 were reviewed. Cases were detected by a review of positive blood cultures reported by the microbiology laboratory. Centers for Disease Control and Prevention definitions of nosocomial infection were used to categorize isolates as nosocomial, community acquired or contaminant.

RESULTS

There were 2389 cases; primary bacteremia was the most common source (57%), followed by urinary tract, respiratory tract and surgical site sources (10% each). The nosocomial blood steam infection rate rose progressively from 6.0/1000 admissions and 4.59/10,000 patient days in 1986 to 11.2/1000 admissions and 14.31/10,000 days in 1996 (P<0.01); 48% of the total increase in rate occurred between 1995 and 1996. Significant increases occurred between 1986 and 1996 in primary infections (from 3.2 to 7.5/1000 admissions, P<0.01) and infections from all secondary sources (from 2.5 to 3.8/1000 admissions, P=0.01). Coagulase-negative staphylococci (27%), Staphylococcus aureus (19%) and enterococci (9%) were the most common microbial causes. Aerobic Gram-negative bacilli accounted for 28% and candida for 6%. Coagulase-negative staphylococci, enterococci and candida all became more prevalent as causes of infection over the study period.

CONCLUSIONS

The nosocomial blood stream infection rate in the hospital has nearly doubled in the past 10 years, largely due to increased primary bacteremia.

Spectrum of practice in the diagnosis of nosocomial pneumonia in patients requiring mechanical ventilation in European intensive care units

OBJECTIVES

Information on clinical practice regarding the diagnosis of pneumonia in European intensive care units is limited. The aim of this study was to describe the spectrum of actual diagnostic practices in a large sample of European intensive care units.

DESIGN

Prospective, observational, multicenter study.

SETTING

Twenty-seven intensive care units of nine European countries.

PATIENTS

Consecutive patients requiring invasive mechanical ventilation for an admission diagnosis of pneumonia or receiving mechanical ventilation for >48 hrs irrespective of admission diagnosis.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A total of 2,436 patients were evaluated; 827 were admitted with or developed nosocomial pneumonia (hospital-acquired pneumonia [HAP], 27.1%; ventilator-associated pneumonia [VAP], 56.2%; very early onset VAP, 16.7%). Mean age was 59.4 +/- 18.1 yrs, 65.0% were men, and mean admission Simplified Acute Physiology Score II was 46.7 +/- 17.1. Worsening oxygenation (76.8%), purulent/changing respiratory secretions (72.1%), and new temperature elevation (69.2%) were the most frequent clinical signs of nosocomial pneumonia. Etiological diagnosis was based on noninvasive respiratory specimens in 74.8% of episodes. Bronchoscopy was performed in 23.3% of episodes. Bronchoscopy performance, after adjustment by severity of illness, age, and type of hospital, were predicted by worsening oxygenation (odds ratio 2.03; 95% confidence interval, 1.27-3.24) and male sex (odds ratio 1.77; 95% confidence interval, 1.19-2.65). Definite cause was documented in 69.5% of nosocomial pneumonia cases. The most common isolates were Staphylococcus aureus (16.3% methicillin-sensitive S. aureus and 16.0% methicillin-resistant S. aureus), Pseudomonas aeruginosa (23.1%), and Acinetobacter baumannii (19.1%). Presence of nosocomial pneumonia significantly prolonged mean length of mechanical ventilation (10.3 days, p < .05) and mean intensive care unit length of stay (12.2 days, p < .05) in intensive care unit survivors. Mortality rate was 37.7% for nosocomial pneumonia vs. 31.6% for patients without pneumonia (p < .05).

CONCLUSIONS

Etiological diagnosis of nosocomial pneumonia in a large sample of European intensive care units was based mainly on noninvasive techniques. However, there was high variability in bronchoscopy use between the participating intensive care units.

Bacteremia in patients with ventilator-associated pneumonia is associated with increased mortality: A study comparing bacteremic vs. nonbacteremic ventilator-associated pneumonia

OBJECTIVE

To assess whether bacteremic ventilator-associated pneumonia (B-VAP) differs in terms of risk factors, organisms, and outcomes from nonbacteremic VAP (NB-VAP).

DESIGN

A retrospective, single-center, observational, cohort study.

SETTING

Multidisciplinary teaching intensive care unit.

PATIENTS

Adult patients requiring mechanical ventilation, identified as having VAP in a 44-month prospective surveillance database.

INTERVENTIONS

Each B-VAP patient was matched with two controls with VAP and negative blood cultures based on the microbial etiology responsible for VAP, Acute Physiology and Chronic Health Evaluation II score on admission (+/-3 points), diagnostic category, and length of stay before pneumonia onset.

MEASUREMENTS AND MAIN RESULTS

B-VAP was documented in 35 (17.6%) of 199 microbiologically confirmed VAP episodes. B-VAP developed later (median 8 vs. 5 days, p = .03) and was more frequent in previously hospitalized patients (34.3% vs. 11.0%, p < .01) and in older patients (57.4 +/- 15.2 vs. 49.5 +/- 19.3 yrs, p = .02). B-VAP was more often caused by methicillin-resistant Staphylococcus aureus (12 [20.7%] vs. 13 [5.1%] episodes, p < .01), whereas Haemophilus influenzae was associated with NB-VAP (52 [20.4%] vs. 0, p < .01). Multivariate analysis confirmed an association between B-VAP and both methicillin-resistant S. aureus (odds ratio 3.18; 95% confidence interval 1.15-8.76, p < .01) and prior hospitalization (odds ratio 2.56; 95% confidence interval 1.01-6.54, p = .05). After adjustment for potential confounders, B-VAP (hazard ratio for death 2.55; 95% confidence interval 1.25-5.23, p = .01) and vasopressor use (hazard ratio 2.43; 95% confidence interval 1.23-4.82, p = .01) remained associated with mortality. The estimated relative risk of death for bacteremic cases was 2.86 (95% confidence interval 1.09-7.51), since mortality for cases and matched NB-VAP controls was 40.6% (13 of 32) and 19.3% (11 of 57), respectively.

CONCLUSIONS

B-VAP occurs later during intensive care unit stay, is more frequent in previously hospitalized patients, is more often caused by methicillin-resistant S. aureus, and is independently associated with increased intensive care unit mortality.

The type III pseudomonal exotoxin U activates the c-Jun NH2-terminal kinase pathway and increases human epithelial interleukin-8 production

Microbial interactions with host cell signaling pathways are key determinants of the host cell response to infection. Many toxins secreted by bacterial type III secretion systems either stimulate or inhibit the host inflammatory response. We investigated the role of type III secreted toxins of the lung pathogen Pseudomonas aeruginosa in the inflammatory response of human respiratory epithelial cells to infection. Using bacteria with specific gene deletions, we found that interleukin-8 production by these cells was almost entirely dependent on bacterial type III secretion of exotoxin U (ExoU), a phospholipase, although other bacterial factors are involved. ExoU activated the c-Jun NH(2)-terminal kinase pathway, stimulating the phosphorylation and activation of mitogen-activated kinase kinase 4, c-Jun NH(2)-terminal kinase, and c-Jun. This in turn increased levels of transcriptionally competent activator protein-1. Although this pathway was dependent on the lipase activity of ExoU, it was independent of cell death. Activation of mitogen-activated kinase signaling by ExoU in this fashion is a novel mechanism by which a bacterial product can initiate a host inflammatory response, and it may result in increased epithelial permeability and bacterial spread.

Neumonía nosocomial en el enfermo no intubado

Hospital-acquired pneumonia is one of the main causes of nosocomial infection. Although its incidence is higher in intubated patients, around half of all cases occur outside the intensive care unit (ICU). However, few studies have been performed in this setting and consequently most data come from hospitalized series that include patients undergoing mechanical ventilation. The epidemiological differences between intubated patients and non-ICU patients suggest that the etiology and therapeutic approach differ between these two groups. The present article reviews the epidemiology, diagnosis, treatment and prevention of nosocomial pneumonia in general wards.

Aportación del laboratorio de microbiología al diagnóstico de la neumonía asociada a la ventilación mecánica

The etiologic diagnosis of ventilator-associated pneumonia (VAP) should be considered as a microbiological emergency due to its impact on morbidity and mortality. Sampling of the lower respiratory tract (LRT) must be performed before starting or modifying antimicrobial therapy. Surveillance cultures in patients without criteria of VAP are not recommended. There is no evidence of any superiority of bronchoscopic over non-bronchoscopic sampling procedures, but quantitative bacterial cultures are essential to allow colonization to be differentiated from true infection of the LRT. Under these conditions, negative cultures practically rule out bacterial infection or, at least, identify patients who will not benefit from antibiotic therapy or who will require a very short course of treatment. Given that identification and antimicrobial susceptibility testing of microorganisms usually takes up to 3 or 4 days, rapid procedures that provide the clinician with useful information are essential. Rapid information, even if partial or less than perfect, is clearly better for the patient than a perfect but delayed report. Gram stain of LRT secretions is an immediate procedure that can guide management and it has a reasonable correlation with culture results. At present, new antibiogram procedures, performed on direct clinical samples, allow presumptive identification and information on susceptibility to commonly used antibiotics in less than 24 hours after sampling. The impact of using this procedure in clinical practice is currently under research.

The spectrum of practice in the diagnosis and management of pneumonia in patients requiring mechanical ventilation. Australian and New Zealand practice in intensive care (ANZPIC II)

This study of ventilated patients investigated current clinical practice in 476 episodes of pneumonia (48% community-acquired pneumonia, 24% hospital-acquired pneumonia, 28% ventilator-associated pneumonia) using a prospective survey in 14 intensive care units (ICUs) within Australia and New Zealand. Diagnostic methods and confidence, disease severity, microbiology and antibiotic use were assessed. All pneumonia types had similar mortality (community-acquired pneumonia 33%, hospital-acquired pneumonia 37% and ventilator-associated pneumonia 24%, P=0.15) with no inter-hospital differences (P=0.08-0.91). Bronchoscopy was performed in 26%, its use predicted by admission hospital (one tertiary: OR 9.98, CI 95% 5.11-19.49, P< 0.001; one regional: OR 6.29, CI 95% 3.24-12.20, P<0.001), clinical signs of consolidation (OR 3.72, CI 95% 2.09-6.62, P<0.001) and diagnostic confidence (OR 2.19, CI 95% 1.29-3.72, P=0.004). Bronchoscopy did not predict outcome (P=0.11) or appropriate antibiotic selection (P=0.69). Inappropriate antibiotic prescription was similar for all pneumonia types (11-13%, P=0.12) and hospitals (0-16%, P=0.25). Blood cultures were taken in 51% of cases. For community-acquired pneumonia, 70% received a third generation cephalosporin and 65% a macrolide. Third generation cephalosporins were less frequently used for mild infections (OR 0.38, CI 95% 0.16-0.90, P=0.03), hospital-acquired pneumonia (OR 0.40, CI 95% 0.23-0.72, P<0.01), ventilator-associated pneumonia (OR 0.04, CI 95% 0.02-0.13, P<0.001), suspected aspiration (OR 0.20, CI 95% 0.04-0.92, P=0.04), in one regional (OR 0.26, CI95% 0.07-0.97, P=0.05) and one tertiary hospital (OR 0.14, CI 95% 0.03-0. 73, P=0.02) but were more commonly used in older patients (OR 1.02, CI 95% 1.01-1.03, P=0.01). There is practice variability in bronchoscopy and antibiotic use for pneumonia in Australian and New Zealand ICUs without significant impact on patient outcome, as the prevalence of inappropriate antibiotic prescription is low. There are opportunities for improving microbiological diagnostic work-up for isolation of aetiological pathogens.

Multicenter study of hospital-acquired pneumonia in non-ICU patients

STUDY OBJECTIVE

To know the incidence, epidemiology, etiology, and outcome of hospital-acquired pneumonia (HAP) in non-ICUs adult patients.

SETTING

Twelve Spanish teaching hospitals.

INTERVENTIONS

From April 1999 to November 2000, non-ICU HAP was prospectively studied by active, bimonthly 1-week surveillance. Epidemiologic data, etiology, and evolution of pneumonia were recorded. Blood and sputum cultures and Legionella pneumophila and Streptococcus pneumoniae urinary antigen tests were performed.

RESULTS

We included 186 patients, with complete data available in 165 patients (70.3% male gender; mean age, 63.7 +/- 16.9 years [ +/- SD]) The mean incidence of HAP was 3 +/- 1.4 cases/1,000 hospital admissions. Most patients (64.2%) were in medical wards, had severe underlying diseases (66.6%), and had a hospital stay > 5 days (76.4%). Blood cultures were performed in 139 patients (84.2%), sputum cultures were performed in 89 patients (53.9%), and urinary antigen detection was performed in 123 patients (74.5%). An etiologic diagnosis was obtained in 60 cases (36.4%), and 31 were definitive. The most frequent etiologies were S pneumoniae (16 cases, 14 definitive), L pneumophila (7 cases, 7 definitive), Aspergillus sp (7 cases, 3 definitive), Pseudomonas aeruginosa (7 cases, 2 definitive), and several Enterobacteriaceae (8 cases, 4 definitive). Clinical complications occurred in 52.1% of the cases, and mortality was 26% (13.9% attributed to pneumonia).

CONCLUSIONS

Non-ICU HAP is an important cause of hospital morbidity, observed most frequently in medical wards and elderly patients with severe underlying diseases. In this setting, S pneumoniae and Legionella sp should be considered in addition to other nosocomial pathogens; urinary antigen detection is useful in determining the prevalence of these microorganisms.

Imagerie moderne des pneumonies infectieuses aiguës

Les pneumonies infectieuses aiguës constituent un problème de santé publique important, car elles sont une cause majeure de morbidité et de mortalité chez l’adulte. Si les données cliniques et radiographiques permettent le plus souvent de faire le diagnostic de pneumonie infectieuse, le diagnostic étiologique est plus difficile. En effet, de nombreux agents pathogènes peuvent être responsables de pneumonie et la réaction du parenchyme pulmonaire est peu variée, d’où la faible spécificité des lésions radiologiques observées en dehors de quelques cas particuliers. C’est pourquoi la compréhension des mécanismes physiopathologiques permet d’expliquer certains aspects radiologiques. De même, la connaissance des bases anatomocliniques et radiologiques autorise la reconnaissance de trois aspects radiographiques principaux. Quant à l’appréciation des contextes épidémiologique et immunitaire, ils peuvent permettre également d’approcher le germe en cause.

Effects of monoclonal anti-PcrV antibody on Pseudomonas aeruginosa-induced acute lung injury in a rat model

BACKGROUND: The effects of the murine monoclonal anti-PcrV antibody Mab166 on acute lung injury induced by Pseudomonas aeruginosa were analyzed in a rat model. METHODS: Lung injury was induced by the instillation of P. aeruginosa strain PA103 directly into the left lungs of anesthetized rats. One hour after the bacterial instillation, rabbit polyclonal anti-PcrV IgG, murine monoclonal anti-PcrV IgG Mab166 or Mab166 Fab-fragments were administered intratracheally directly into the lungs. The degree of alveolar epithelial injury, amount of lung edema, decrease in oxygenation and extent of lung inflammation by histology were evaluated as independent parameters of acute lung injury. RESULTS: These parameters improved in rats that had received intratracheal instillation of either rabbit polyclonal anti-PcrV IgG, murine monoclonal anti-PcrV IgG Mab166 or Mab166 Fab-fragments in comparison with the control group. CONCLUSION: Mab166 and its Fab fragments have potential as adjuvant therapy for acute lung injury due to P. aeruginosa pneumonia.

Effects of Cl2MDP-encapsulating liposomes in a murine model of Pseudomonas aeruginosa-induced sepsis

Pseudomonas aeruginosa is a pathogen that frequently causes acute lung injury, bacteremia and sepsis in critically ill patients. As tissue macrophages are a major producer of inflammatory mediators that contribute to septic physiology, and are essential for eliminating bacteria from the circulation, we investigated the role of tissue macrophages in the generation of both inflammatory and anti-inflammatory cytokines in septic shock by using our mouse model of P. aeruginosa pneumonia. To see the effects of tissue macrophage depletion, we intravenously injected dichloromethylene-diphosphonate (Cl2MDP)-encapsulating liposomes in mice. Two days after the liposome injection, we instilled cytotoxic P. aeruginosa (PA103) into the lung that disseminates and causes septic shock. After the infection, we collected blood and bronchoalveolar lavage fluids. The samples were then analyzed for TNF-alpha, MIP-2, and IL-10 concentration. We compared these results to control mice that received either liposomes without Cl2MDP or phosphate buffered saline alone. Plasma TNF-alpha, MIP-2, and IL-10 levels were significantly decreased in the tissue macrophage-depleted mice compared to the control groups of mice. Although depletion of tissue macrophages by Cl2MDP-liposome administration did not affect the severity of bacteremia or the survival of infected mice, these results imply that tissue macrophages have a major role in the production of both proinflammatory and anti-inflammatory cytokines in the circulation and in the causing septic physiology associated with P. aeruginosa pneumonia.

Imaging of pneumonia: trends and algorithms

Pneumonia is one of the major infectious diseases responsible for significant morbidity and mortality throughout the world. Imaging plays a crucial role in the detection and management of patients with pneumonia. This review article discusses the different imaging methods used in the diagnosis and management of suspected pulmonary infections. The imaging examination should always begin with conventional radiography. When the results of routine radiography are inconclusive, computed tomography is mandatory. A combination of pattern recognition with knowledge of the clinical setting is the best approach to the pulmonary infectious processes. A specific pattern of involvement can suggest a likely diagnosis in many instances. In acquired immune deficiency syndrome patients, diffuse ground-glass and interstitial infiltrates are most commonly present in Pneumocystis carinii pneumonia whereas in the nonimmunosuppressed patients, a segmental lobar infiltrate is suggestive of a bacterial pneumonia. Round pneumonia is most often encountered in children than adults and is most often caused by Streptococcus pneumoniae. Different combinations of parenchymal and pleural abnormalities may be suggestive for additional diagnoses. When an infectious pulmonary process is suspected, knowledge of the varied radiographic manifestations will narrow the differential diagnosis, helping to direct additional diagnostic measures, and serving as an ideal tool for follow-up examinations.

Effects of antibiotic therapy on Pseudomonas aeruginosa-induced lung injury in a rat model

The effect of antibiotics on the acute lung injury induced by virulent Pseudomonas aeruginosa PA103 was quantitatively analyzed in a rat model. Lung injury was induced by the instillation of PA103 directly into the right lower lobes of the lungs of anesthetized rats. The alveolar epithelial injury, extravascular lung water, and total plasma equivalents were measured as separate, independent parameters of acute lung injury. Four hours after the instillation of PA103, all the parameters were increased linearly depending on the dose of P. aeruginosa. Next, we examined the effects of intravenously administered antibiotics on the parameters of acute lung injury in D-galactosamine-sensitized rats. One hour after the rats received 10(7) CFU of PA103, an intravenous bolus injection of aztreonam (60 mg/kg) or imipenem-cilastatin (30 mg/kg) was administered. Despite an MIC indicating resistance, imipenem-cilastatin improved all the measurements of lung injury; in contrast, aztreonam, which had an MIC indicating sensitivity, did not improve any of the lung injury parameters. The antibiotics did not generate different quantities of plasma endotoxin; therefore, endotoxin did not appear to explain the differences in lung injury. This in vivo model is useful to quantitatively compare the efficacies of parenteral antibiotic administration on Pseudomonas airspace infections.

Blood cultures have limited value in predicting severity of illness and as a diagnostic tool in ventilator-associated pneumonia

STUDY OBJECTIVES

To define the usefulness of blood cultures for confirming the pathogenic microorganism and severity of illness in patients with ventilator-associated pneumonia (VAP).

DESIGN

Prospective observational study using BAL and blood cultures collected within 24 h of establishing a clinical diagnosis of VAP.

SETTING

A 15-bed medical and surgical ICU.

PATIENTS

One hundred and sixty-two patients receiving mechanical ventilation hospitalized for > 72 h who had new or progressive lung infiltrate plus at least two of three clinical criteria for VAP.

INTERVENTIONS

BAL and blood culture performed within 24 h of establishing a clinical diagnosis of VAP.

MEASUREMENTS AND RESULTS

Ninety patients were BAL positive (BAL+), satisfying a microbiological definition of VAP (>/= 10(4) cfu/mL), 72 patients were BAL negative (BAL-). Bacteremia was diagnosed when at least two sets of blood cultures yielded a microorganism or when only one set was positive, but the same bacteria was present at a concentration >/= 10(4) cfu/mL in the BAL fluid. Bacteremia was significantly more frequent in the BAL+ than in the BAL- group (22/90 patients vs 5/72 patients; p = 0.006). In 6 of 22 BAL+ patients with bacteremia, an extrapulmonary site of infection was the source of bacteremia. Sensitivity of blood culture for disclosing the pathogenic microorganism in BAL+ patients was 26%, and the positive predictive value to detect the pathogen was 73%. Factors associated with mortality were age > 50 years, simplified acute physiology score > 14, prior inadequate antibiotic therapy, PaO(2)/fraction of inspired oxygen < 205, and use of H(2) blockers. By multivariate analysis, only the use of prior inadequate antimicrobial therapy (odds ratio [OR], 6.47) and age > 50 years (OR, 5.12) were independently associated with higher mortality. The rate of complications was not different in patients with bacteremia.

CONCLUSIONS

Blood cultures have a low sensitivity for detecting the same pathogenic microorganism as BAL culture in patients with VAP. The presence of bacteremia does not predict complications, it is not related to the length of stay, and it does not identify patients with more severe illness. Inadequacy of prior antimicrobial therapy and age > 50 years were the only factors associated with mortality in a multivariate analysis. Blood cultures in patients with VAP are clearly useful if there is suspicion of another probable infectious condition, but the isolation of a microorganism in the blood does not confirm that microorganism as the pathogen causing VAP.

Pathogenesis of septic shock in Pseudomonas aeruginosa pneumonia

The pathogenesis of septic shock occurring after Pseudomonas aeruginosa pneumonia was studied in a rabbit model. The airspace instillation of the cytotoxic P. aeruginosa strain PA103 into the rabbit caused a consistent alveolar epithelial injury, progressive bacteremia, and septic shock. The lung instillation of a noncytotoxic, isogenic mutant strain (PA103DeltaUT), which is defective for production of type III secreted toxins, did not cause either systemic inflammatory response or septic shock, despite a potent inflammatory response in the lung. The intravenous injection of PA103 did not cause shock or an increase in TNF-alpha, despite the fact that the animals were bacteremic. The systemic administration of either anti-TNF-alpha serum or recombinant human IL-10 improved both septic shock and bacteremia in the animals that were instilled with PA103. Radiolabeled TNF-alpha instilled in the lung significantly leaked into the circulation only in the presence of alveolar epithelial injury. We conclude that injury to the alveolar epithelium allows the release of proinflammatory mediators into the circulation that are primarily responsible for septic shock. Our results demonstrate the importance of compartmentalization of inflammatory mediators in the lung, and the crucial role of bacterial cytotoxins in causing alveolar epithelial damage in the pathogenesis of acute septic shock in P. aeruginosa pneumonia.

Prospective randomized comparison of imipenem-cilastatin and piperacillin-tazobactam in nosocomial pneumonia or peritonitis

Nosocomial pneumonia and acute peritonitis may be caused by a wide array of pathogens, and combination therapy is often recommended. We have previously shown that imipenem-cilastatin monotherapy was as efficacious as the combination of imipenem-cilastatin plus netilmicin in these two settings. The efficacy of imipenem-cilastatin is now compared to that of piperacillin-tazobactam as monotherapy in patients with nosocomial pneumonia or acute peritonitis. Three hundred seventy one patients with nosocomial pneumonia or peritonitis were randomly assigned to receive either imipenem-cilastatin (0.5 g four times a day) or piperacillin-tazobactam (4.5 g three times a day). Three hundred thirteen were assessable (154 with nosocomial pneumonia and 159 with peritonitis). For nosocomial pneumonia, clinical-failure rates in the piperacillin-tazobactam group (13 of 75 [17%]) and in the imipenem-cilastatin group (23 of 79 [29%]) were similar (P = 0.09), as were the numbers of deaths due to infection (6 in the imipenem-cilastatin group [8%], 7 in the piperacillin-tazobactam group [9%]) (P = 0.78). For acute peritonitis, clinical success rates were comparable (piperacillin-tazobactam, 72 of 76 [95%]; imipenem-cilastatin, 77 of 83 [93%]). For infections due to Pseudomonas aeruginosa, 45 patients had nosocomial pneumonia (21 in the piperacillin-tazobactam group and 24 in the imipenem-cilastatin group) and 10 had peritonitis (5 in each group). In the patients with nosocomial pneumonia, clinical failure was less frequent in the piperacillin-tazobactam group (2 of 21 [10%]) than in the imipenem-cilastatin [corrected] group (12 of 24 [50%]) (P = 0.004). Bacterial resistance to allocated regimen was the main cause of clinical failure (1 in the piperacillin-tazobactam group and 12 in the imipenem-cilastatin group). For the patients with peritonitis, no difference in clinical outcome was observed (five of five cured in each group). The overall frequencies of adverse events related to treatment in the two groups were similar (24 in the piperacillin-tazobactam group, 22 in the imipenem-cilastatin group). Diarrhea was significantly more frequent in the piperacillin-tazobactam group (10 of 24) than in the imipenem-cilastatin group (2 of 22). This study suggests that piperacillin-tazobactam monotherapy is at least as effective and safe as imipenem-cilastatin monotherapy in the treatment of nosocomial pneumonia or peritonitis. In P. aeruginosa pneumonia, piperacillin-tazobactam achieved a better clinical efficacy than imipenem-cilastatin, due to reduced development of microbiological resistance. Tolerance was comparable, with the exception of diarrhea, which was more frequent with piperacillin-tazobactam.

Clinical and epidemiological findings in mechanically-ventilated patients with methicillin-resistant Staphylococcus aureus pneumonia

Over the 5-year period from 1990 to 1994, a prospective cohort study was conducted to define the clinical and epidemiological characteristics of ventilator-associated methicillin-resistant Staphylococcus aureus (MRSA) pneumonia acquired during a large-scale outbreak of MRSA infection. Of 2411 mechanically ventilated patients, 347 (14.4%) acquired MRSA, 220 (63.4%) had MRSA positive respiratory tract samples and 41 (18.6%) developed ventilator-associated MRSA pneumonia. The overall attack rate for ventilator-associated MRSA pneumonia was 1.56 episodes/1000 ventilator days, but annual attack rates varied according to the trend of the outbreak (range 4.9-0.2). In comparison with methicillin-sensitive Staphylococcus aureus (MSSA), which was implicated in 98 episodes of ventilator-associated pneumonia, MRSA caused exclusively late-onset ventilator-associated pneumonia, while MSSA caused both early-onset [55 of 98 (56.1%) episodes] and late-onset [43 of 98 (43.8%) episodes] ventilator-associated pneumonia. Logistic regression analysis of all patients with Staphylococcus aureus pneumonia revealed intubation for more than 3 days (odds ratio (OR),1.11; confidence interval (CI):1.03-1.18) and prior bronchoscopy (OR,5.8; CI,1.85-18.19) to be independent variables associated with MRSA pneumonia. The results indicate that MRSA ventilator-associated pneumonia is a frequent complication in intensive care patients, manifesting itself as late-onset pneumonia in patients who have been intubated for prolonged periods and/or have often undergoing previous bronchoscopy.

Resistance issues and treatment implications: pneumococcus, Staphylococcus aureus, and gram-negative rods

During the last decade there has been an unexpectedly rapid evolution of antimicrobial resistance in the respiratory pathogens for community- and hospital-acquired pneumonia. In order to choose the most optimal therapy for their patients, it is essential that physicians be aware of the prevalence and mechanisms of resistance and their implications on the effectiveness of the various antimicrobials.

In vitro cellular toxicity predicts Pseudomonas aeruginosa virulence in lung infections

The role of quorum sensing by Pseudomonas aeruginosa in producing cytotoxicity has not been fully investigated. Strains of P. aeruginosa have been characterized as having an invasive or a cytotoxic phenotype (S. M. J. Fleiszig et al., Infect. Immun. 65:579-586, 1997). We noted that the application of a large inoculum of the invasive strain 6294 caused cytotoxicity of cultured epithelial cells. To investigate this dose-related cytotoxicity, we compared the behavior of 6294 to that of another invasive strain, PAO1, and determined whether the cytotoxicity could be related to quorum sensing. Both invasive strains, 6294 and PAO1, appear to have quorum-sensing systems that were operative when large doses of bacteria were applied to cultured lung epithelial cells or instilled into the lungs of animals. Nonetheless, only 6294 was cytotoxic. Cytotoxicity induced by 6294 correlated with increased elastase production. These experiments suggest that there are multiple mechanisms for the induction of cytotoxicity, pathology, and mortality in vivo. However, in vivo cytotoxicity and mortality, but not pathology, could be predicted by quantitative in vitro cellular damage experiments utilizing a range of bacteria-to-cell ratios. It appears that quorum sensing may inversely correlate with virulence in that strains that produced PAI [N-(3-oxododecanoyl) homoserine lactone] also appeared to attract more polymorphonuclear leukocytes in vivo and were possibly eliminated more quickly. In addition, exoproduct production in bacteriological medium in vitro may differ significantly from exoproduct expression from infections in vivo or during cocultivation of bacteria with tissue culture cells.

Hospital-acquired pneumonia: methicillin resistance and intensive care unit admission

Although epidemiologic investigations of hospital-acquired pneumonia have certain intrinsic limitations because of the heterogeneity of the study populations, the difficulties in making a clinical diagnosis of nosocomial pneumonia, and the need for better microbiologic assays, recent studies have provided new and important data concerning the role of Staphylococcus aureus in this disease. This pathogen has now been identified as the most frequent cause of nosocomial pneumonia in hospitals in both Europe and the United States among patients in general hospital units as well as in the intensive care unit (ICU). Patients who have been treated with mechanical ventilation are at especially high risk for S. aureus pneumonia. The incidence of nosocomial pneumonia related to methicillin-resistant S. aureus (MRSA) has increased in recent years in many countries, especially among patients in the ICU. Because hospitalized patients with suspected nosocomial pneumonia often have many risk factors for MRSA infection, it seems advisable to include coverage of MRSA in the initial therapeutic regimen for these patients until MRSA infection is excluded.