Role of quantitative cultures and microscopic examinations of endotracheal aspirates in the diagnosis of pulmonary infections in ventilated patients

Detection of Eight Respiratory Bacterial Pathogens Based on Multiplex Real-Time PCR with Fluorescence Melting Curve Analysis

Background and Objective. Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae, Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, Pseudomonas aeruginosa, and Mycobacterium tuberculosis are primary respiratory bacterial pathogens contributing to morbidity and mortality in developing countries. This study evaluated the diagnostic performance of multiplex real-time PCR with fluorescence melting curve analysis (MCA) assay, which was used to detect eight respiratory bacterial pathogens simultaneously.

Methods

A total of 157 sputum specimens were examined by multiplex real-time with fluorescence MCA, and the results were compared with the conventional culture method.

Results

Multiplex real-time PCR with fluorescence MCA specifically detected and differentiated eight respiratory bacterial pathogens by different melting curve peaks for each amplification product within 2 hours and exhibited high repeatability. The limit of detection ranged from 64 to 10² CFU/mL in the multiplex PCR system. Multiplex real-time PCR with fluorescence MCA showed a sensitivity greater than 80% and a 100% specificity for each pathogen. The kappa correlation of eight bacteria ranged from 0.89 to 1.00, and the coefficient of variation ranged from 0.05% to 0.80%.

Conclusions

Multiplex real-time PCR with fluorescence MCA assay is a sensitive, specific, high-throughput, and cost-effective method to detect multiple bacterial pathogens simultaneously.

The Use of Procalcitonin for Prediction of Pulmonary Bacterial Coinfection in Children With Respiratory Failure Associated With Viral Bronchiolitis

Objectives. Viral bronchiolitis is a frequent cause of pediatric hospitalization and respiratory failure. Procalcitonin (PCT) is a biomarker used to identify serious bacterial infection and can distinguish bacterial and viral infections. Concomitant bacterial pneumonia is not rare in viral bronchiolitis and can lead to a worse clinical course. This study examined the use of PCT in pediatric patients with respiratory failure attributed to viral bronchiolitis to predict concomitant bacterial pneumonia. Methods. This prospective descriptive study evaluated children less than 4 years of age who underwent endotracheal intubation for respiratory failure due to viral bronchiolitis. PCT levels and endotracheal aspirate cultures were obtained at admission. Bacterial pneumonia was defined as at least moderate growth of a single pathogenic organism from endotracheal culture. PCT levels were evaluated in groups with and without concomitant bacterial pneumonia. Results. Thirty-five patients were enrolled between February 2013 and May 2015. All subjects tested positive for at least 1 viral pathogen by nasal wash polymerase chain reaction or enzyme immunoassay. The top viruses obtained were respiratory syncytial virus (n = 15, 42.8%) and rhinovirus (n = 8, 22.9%). The incidence of bacterial pneumonia was 60% (21/35). The PCT median was 0.93 ng/mL (interquartile range = 0.25-6.64) in the bacterial pneumonia group and 1.85 ng/mL (interquartile range = 0.28-7.94) in the nonbacterial pneumonia group. No correlation was found between PCT and bronchiolitis with bacterial coinfection (P = .74). Conclusion. Incidence of bacterial coinfection in patients with respiratory failure and viral bronchiolitis was high. PCT did not predict concomitant bacterial pneumonia in children with viral bronchiolitis.

Use of Tracheal Aspirate Culture in Newly Intubated Patients with Community-Onset Pneumonia

RATIONALE

Successful treatment of life-threatening community-acquired pneumonia requires appropriate empiric antibiotic coverage. But using conventional diagnostic techniques, a microbiological diagnosis is often not achieved. The diagnostic usefulness of tracheal aspirate at the time of intubation in patients with severe pneumonia has not been well studied.

OBJECTIVES

The purpose of this study was to evaluate the use of tracheal aspirate culture in identifying pneumonia pathogens.

METHODS

We identified all patients older than 18 years of age with International Classification of Disease, Ninth Revision codes and radiographic evidence of pneumonia seen in the emergency departments at 2 university-affiliated Utah hospitals from December 2009 to November 2010 and from December 2011 to November 2012. Patients intubated within 24 hours of arrival were then identified electronically. Postintubation orders instructed respiratory therapists to obtain tracheal aspirate for culture. All culture results were reviewed individually and defined as positive if a pneumonia pathogen was identified. Results of other microbiology studies were obtained from the electronic medical record.

MEASUREMENTS AND MAIN RESULTS

Of 2,011 patients with pneumonia, 94 were intubated and 84 had a tracheal aspirate obtained. Of these 84 patients, 47 (56%) had a pulmonary pathogen identified by tracheal aspirate culture, 80 also had blood cultures, and 71 underwent Pneumococcal and Legionella urinary antigen testing. A microbiological diagnosis was made in 55 patients (65.5%) by any diagnostic method. In 39% of patients (32 of 82), the tracheal aspirate culture was the only positive test, resulting in a unique microbiological diagnosis in patients who would have otherwise been classified as "culture negative."

CONCLUSIONS

Tracheal aspirate cultures obtained as part of routine care identified a plausible pneumonia pathogen in more than one-half of emergency department adult patients with severe pneumonia requiring intubation. Tracheal aspirate culture offers important additive diagnostic value to other routine tests.

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.

Usefulness of quantitative endotracheal aspirate cultures in intensive care unit patients with suspected pneumonia

It is difficult to differentiate pathogens responsible for pneumonia or colonization in patients with an endotracheal tube or in patients that have undergone tracheostomy. We evaluated the clinical usefulness of quantitative endotracheal aspirates cultures and sought to determine the result threshold level for positivity. The authors performed this retrospective cohort study between December 1, 2004 and January 31, 2006. Forty-five suspected pneumonia patients admitted to an intensive care unit (ICU) with quantitative bronchoalveolar lavage (BAL) and endotracheal aspirate (EA) culture results were enrolled. Using a threshold of 10(5) cfu/mL, 10 of the 45 (22.2%) quantitative EA cultures were positive, as compared with 7 (15.6%) BAL cultures. When BAL culture findings were used as the reference, the sensitivity and specificity of quantitative EA cultures were 85.7% and 89.5%, respectively, at a threshold of 10(5) cfu/mL, and 85.7% and 94.7%, respectively, at a threshold of 10(6) cfu/mL. Of the 10 EA culture positive patients, 2 patients with a result of -10(5) cfu/mL were BAL culture negative. The quantitative EA culture is a useful non-invasive tool for the diagnosis of pneumonia pathogens. It is suggested that a threshold level of 10(6) cfu/mL is appropriate.

Novel in vitro pharmacodynamic model simulating ofloxacin pharmacokinetics in the treatment of Pseudomonas aeruginosa biofilm-associated infections

OBJECTIVES

The conventional in vitro models simulate pharmacodynamics of antibiotics in the treatment of planktonic Pseudomonas aeruginosa. In this study, we propose a novel pharmacodynamic model of ofloxacin activity in the treatment of P. aeruginosa biofilm.

METHODS

P. aeruginosa biofilm carrying coupons were suspended in a continuous flow central compartment bioreactor (CCB). In the CCB, the pharmacokinetics of different ofloxacin dosing regimens were simulated. Samples from the coupons and the CCB were assessed for viability of the biofilm and the shedding planktonic cells, respectively, over 24h. In addition, ofloxacin concentrations were assessed in each sample withdrawn for the CCB using bioassay method.

RESULTS

The microbiological outcomes on P. aeruginosa biofilm and the shedding planktonic cells in response to different ofloxacin dosing regimens were not parallel and this may explain the non-coincidence of microbiological and clinical outcomes with biofilm associated infections.

CONCLUSION

The current study has introduced unprecedented novel dynamic model for the assessment of the microbiological outcome on both biofilm and shedding planktonic cells of P. aeruginosa in response to different dosing regimens of ofloxacin which in turn can simulate the clinical outcomes in biofilm associated infections of P. aeruginosa, e.g. cystic fibrosis. Furthermore, different scenarios of antibiotic dosing regimens against biofilm related infections can be mimicked using such model.

PER-1- and OXA-10-like beta-lactamases in ceftazidime-resistant Pseudomonas aeruginosa isolates from intensive care unit patients in Istanbul, Turkey

The presence of PER-1- and OXA-10-like beta-lactamases was investigated by PCR in 49 ceftazidime-resistant Pseudomonas aeruginosa isolates from patients hospitalised in the 24-bed general intensive care unit of the Istanbul Faculty of Medicine during a 12-month period between February 1999 and February 2000. The clonal relatedness of the isolates was investigated by random amplified polymorphic DNA (RAPD) analysis, and the sequences of the PER-1 and OXA genes from all isolates were determined. The rates of resistance of the isolates to imipenem, aztreonam and cefepime were 98%, 92% and 96%, respectively, and to piperacillin and piperacillin-tazobactam were 41% and 37%, respectively. Using the double-disk synergy test, 37% (18/49) of the isolates were identified as extended-spectrum beta-lactamase producers. The PER-1 gene was identified in 86% (42/49) and the OXA-10 gene in 55% (27/49) of the ceftazidime-resistant isolates. Of isolates carrying the PER-1 gene, 48% (20/42) also carried the OXA-10 gene. The respective nucleotide sequences were identical for each isolate. Sixteen RAPD patterns were detected among the PER-1-positive isolates, but 60% (25/42) of the PER-1-positive isolates belonged to two distinct patterns, while the remainder exhibited a wide clonal diversity. The results indicated that the prevalence of PER-1- and OXA-10-like beta-lactamases remains high among ceftazidime-resistant P. aeruginosa isolates in Turkey.

Ventilator associated pneumonia: comparison between quantitative and qualitative cultures of tracheal aspirates

Introduction

Deferred or inappropriate antibiotic treatment in ventilator-associated pneumonia (VAP) is associated with increased mortality, and clinical and radiological criteria are frequently employed to establish an early diagnosis. Culture results are used to confirm the clinical diagnosis and to adjust or sometimes withdraw antibiotic treatment. Tracheal aspirates have been shown to be useful for these purposes. Nonetheless, little is known about the usefulness of quantitative findings in tracheal secretions for diagnosing VAP.

Methods

To determine the value of quantification of bacterial colonies in tracheal aspirates for diagnosing VAP, we conducted a prospective follow-up study of 106 intensive care unit patients who were under ventilatory support. In total, the findings from 219 sequential weekly evaluations for VAP were examined. Clinical and radiological parameters were recorded and evaluated by three independent experts; a diagnosis of VAP required the agreement of at least two of the three experts. At the same time, cultures of tracheal aspirates were analyzed qualitatively and quantitatively (10⁵ colony-forming units [cfu]/ml and 10⁶ cfu/ml)

Results

Quantitative cultures of tracheal aspirates (10⁵ cfu/ml and 10⁶ cfu/ml) exhibited increased specificity (48% and 78%, respectively) over qualitative cultures (23%), but decreased sensitivity (26% and 65%, respectively) as compared with the qualitative findings (81%). Quantification did not improve the ability to predict a diagnosis of VAP.

Conclusion

Quantitative cultures of tracheal aspirates in selected critically ill patients have decreased sensitivity when compared with qualitative results, and they should not replace the latter to confirm a clinical diagnosis of VAP or to adjust antimicrobial therapy.

Impact of introducing quality control/quality assurance (QC/QA) guidelines in respiratory specimen processing

OBJECTIVES

To assess the impact of the introduction of a new quality control/quality assurance (QA/QC) protocol on the processing and reporting of respiratory specimens.

METHODS

After implementation of guidelines for processing respiratory specimens, an investigation was carried out over a six-month period on 200 specimens, 105 sputa, and 95 deep tracheal aspirates (DTAs), assessed blindly by two independent investigators. Data regarding disagreement were arranged into two subgroups. A minor disagreement was defined as a difference in the two assessments of < 10 or 10-25 for white blood cell (WBC) or squamous epithelial cell (SEC) counts. A major disagreement was defined as one assessor reporting < 10 and the other > 25 for either WBC count or SEC count, or one assessor reporting the specimen as non-assessable, or both assessors having a minor disagreement in both the WBC count and the SEC count.

RESULTS

Agreement was obtained on 111 samples. For 45 specimens, a major disagreement was documented, and in 44 cases, a minor disagreement was recorded, WBC being the most common cause of divergence. Data for sputa and DTAs were examined separately: of 45 major disagreements, 64.4% were observed for DTAs, while minor disagreements were recorded mostly for sputa. The role of the settings in which samples were taken in affecting quality was studied. Among the 105 sputa, 27 were from Community Health Centers (CHCs) and 78 from hospitalized patients. Agreement between the two observers was obtained in 48.1% of CHC cases versus 60.2% of hospital samples. To investigate how many of the rejected samples presented WBC > 25 suggestive of infection, we looked at the 107 samples rejected during the six-month period, grouped according to the suspected diagnosis. The highest number of rejected samples falls in the category of unrelated (non-respiratory) diagnosis, and clinical suspicion is not helpful in Gram stain interpretation. The annual saving (not culturing, not testing, and not treating) derived from this simple QC procedure totals about 5000 Euro.

CONCLUSIONS

Standardization in microscopic screening of respiratory samples is difficult to achieve. Criteria for rejection must be adapted to local conditions after discussion with clinicians to increase their compliance with the newly introduced guidelines and to avoid sending unnecessary specimens. The effects on patient management and cost control are significant.

Clinical significance of potential pathogenic microorganisms of sputum in patients with pulmonary tuberculosis

BACKGROUND

Bacterial culture of sputum is frequently positive in patients with pulmonary tuberculosis (TB). However, it remains to be clarified whether detection of potential pathogenic microorganisms (PPM) in sputum represents bacterial infection or only colonization of the respiratory tract. In the present study, we investigated the clinical significance of PPM in patients with pulmonary TB.

METHODOLOGY

Sputum culture for PPM was studied in 174 pulmonary TB patients (117 males and 57 females, mean age of 71 years) on the day of admission. Ninety-seven patients (63 males and 34 females, mean age of 67.1 years) also underwent transtracheal aspirates (TTA). Quantitative culture of sputum and TTA was performed to distinguish infection from colonization. The results were evaluated as follows: more than 106 or 105 c.f.u./mL indicated infection in the case of sputum or TTA samples, respectively. We also compared various clinical parameters between patients with PPM and patients with non-potential pathogenic microorganisms (non-PPM).

RESULTS

Potential pathogenic microorganisms were positive in 44% and 24% of sputum and TTA specimens, respectively. However, quantitative culture for PPM showed positive findings in only 11% and 3% of sputum and TTA specimens, respectively. A comparative study of the clinical features revealed that PPM patients had a lower bodyweight and lower serum albumin levels than non-PPM patients. A fatal outcome was also more common in PPM patients than in non-PPM patients. Logistic regression analysis further confirmed that PPM clearly contributed to a fatal outcome in addition to the previously established parameters including age, performance status, haemoglobin, albumin and radiographic disease extent.

CONCLUSION

Although sputum PPM represent only colonization of the upper respiratory tract in TB patients, they are associated with a poor prognosis.

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

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

Candida colonization in mechanically ventilated patients

The diagnosis of pulmonary candidosis is controversial. We undertook a prospective study on 50 mechanically ventilated (>48 h) patients who were hospitalized (>72 h) in the intensive care unit (ICU) with the aim of assessing the incidence of the isolation of Candida species from endotracheal aspirates (EA). Patients were categorized as individuals already colonized with Candida spp. on admission, individuals becoming colonized during hospitalization, or patients with no colonization. Patients in the ICU were hospitalized for a mean of 23 days. The percentage of patients already colonized with Candida was low (six of 50; 12%), the incidence of Candida isolation from EA in critically ill, mechanically ventilated patients in ICU was also low (six of 50; 12%). Age, duration of hospitalization, pre-treatment with antimicrobials or immunosuppressive agents and occurrence of underlying disease were not risk factors in our study. Both antifungal usage and neutropenia were more common in already colonized patients. No risk factors were determined for patients colonized during hospitalization. As all the isolates identified were C. albicans. It appears that at present, colonization and/or infection by more resistant Candida species is not a problem in our unit.