Predictive value of broncho-alveolar lavage fluid Gram's stain in the diagnosis of ventilator-associated pneumonia: a prospective study

A Bibliometric Analysis of the Role and Research Trending of Bronchoalveolar Lavage in the Diagnosis and Treatment of Ventilator-Associated Pneumonia

Ventilator-associated pneumonia (VAP) is one of the most common complications in intensive care units (ICUs) and negatively affects patient outcomes. Despite its widespread use as a diagnostic and therapeutic measure, the application and effectiveness of bronchoalveolar lavage (BAL) in the management of VAP require further exploration. This study aimed to evaluate the research dynamics, major trends, and scientific networks of BAL in the diagnosis and treatment of VAP using bibliometric analysis. Literature from the Web of Science database on BAL for the diagnosis and treatment of VAP from 1990 to 2024 was screened and analyzed. Keyword co-occurrence, trend analysis, and citation burst analyses were conducted using CiteSpace to identify research hotspots, core authors, institutions, and countries, as well as the evolution of research domains. The bibliometric analysis included 968 publications. Trend analysis indicated growing interest in BAL techniques, particularly in the categories of RESPIRATORY SYSTEM (burst score: 27.82) and MEDICINE, RESEARCH, and EXPERIMENTAL (burst score: 7.41). The co-citation analysis highlighted influential authors in the field, such as Torres (burst score: 9.35), Croce (burst score: 5.86), and Meduri (burst score: 5.71). Keyword analysis results revealed core clusters in the treatment of VAP with BAL, including "nonbronchoscopic lavage" (silhouette value: 0.703), "ICU-acquired infection" (silhouette value: 0.7), and "ventilator-associated tracheobronchitis" (silhouette value: 0.637). Additionally, geographic analysis showed that North America and Europe dominated the research in this field. Recently, research trends regarding protected specimen brushes and quantitative culture techniques have emerged. This study found broad applications of BAL in VAP management, especially in improving diagnostic accuracy and treatment outcomes. Optimized strategies such as improvement of lavage techniques and multidisciplinary collaboration may emerge as potential research hotspots in the future.

Systematic review of studies investigating ventilator associated pneumonia diagnostics in intensive care

Background

Ventilator-associated pneumonia (VAP) is an important diagnosis in critical care. VAP research is complicated by the lack of agreed diagnostic criteria and reference standard test criteria. Our aim was to review which reference standard tests are used to evaluate novel index tests for suspected VAP.

Methods

We conducted a comprehensive search using electronic databases and hand reference checks. The Cochrane Library, MEDLINE, CINHAL, EMBASE, and web of science were searched from 2008 until November 2018. All terms related to VAP diagnostics in the intensive treatment unit were used to conduct the search. We adopted a checklist from the critical appraisal skills programme checklist for diagnostic studies to assess the quality of the included studies.

Results

We identified 2441 records, of which 178 were selected for full-text review. Following methodological examination and quality assessment, 44 studies were included in narrative data synthesis. Thirty-two (72.7%) studies utilised a sole microbiological reference standard; the remaining 12 studies utilised a composite reference standard, nine of which included a mandatory microbiological criterion. Histopathological criteria were optional in four studies but mandatory in none.

Conclusions

Nearly all reference standards for VAP used in diagnostic test research required some microbiological confirmation of infection, with BAL culture being the most common reference standard used.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12890-021-01560-0.

Correlation between Either Cupriavidus or Porphyromonas and Primary Pulmonary Tuberculosis Found by Analysing the Microbiota in Patients' Bronchoalveolar Lavage Fluid

Pulmonary tuberculosis (TB) has gained attention in recent decades because of its rising incidence trend; simultaneously, increasing numbers of studies have identified the relationship between microbiota and chronic infectious diseases. In our work, we enrolled 32 patients with primary TB characterised by unilateral TB lesion formation diagnosed by chest radiographic exam. Bronchoalveolar lavage fluid was taken from both lungs. Twenty-four healthy people were chosen as controls. Pyrosequencing was performed on the V3 hypervariable region of 16S rDNA in all bacterial samples and used as a culture-independent method to describe the phylogenetic composition of the microbiota. Through pyrosequencing, 271,764 amplicons were detected in samples and analysed using tools in the Ribosomal Database Project (RDP) and bioinformatics. These analyses revealed significant differences in the microbiota in the lower respiratory tract (LRT) of TB patients compared with healthy controls; in contrast, the microbiota of intra/extra-TB lesions were similar. These results showed that the dominant bacterial genus in the LRT of TB patients was Cupriavidus and not Streptococcus, which resulted in a significant change in the microbiota in TB patients. The abundance of Mycobacteria and Porphyromonas significantly increased inside TB lesions when compared with non-lesion-containing contralateral lungs. From these data, it can be concluded that Cupriavidus plays an important role in TB's secondary infection and that in addition to Mycobacteria, Porphyromonas may also be a co-factor in lesion formation. The mechanisms underlying this connection warrant further research.

Accuracy of tracheal aspirate gram stain in predicting Staphylococcus aureus infection in ventilator-associated pneumonia

BACKGROUND

The Gram stain can be used to direct initial empiric antimicrobial therapy when complete culture is not available. This rapid test could prevent the initiation of inappropriate therapy and adverse outcomes. However, several studies have attempted to determine the value of the Gram stain in the diagnosis and therapy of bacterial infection in different populations of patients with ventilator-associated pneumonia (VAP) with conflicting results. The objective of this study is to evaluate the accuracy of the Gram stain in predicting the existence of Staphylococcus aureus infections from cultures of patients suspected of having VAP.

METHODS

This prospective single-center open cohort study enrolled 399 patients from December 2005 to December 2010. Patients suspected of having VAP by ATS IDSA criteria were included. Respiratory secretion samples were collected by tracheal aspirate (TA) for standard bacterioscopic analysis by Gram stain and culture.

RESULTS

Respiratory secretion samples collected by tracheal aspirates of 392 patients were analyzed by Gram stain and culture. When Gram-positive cocci were arranged in clusters, the sensitivity was 68.4%, specificity 97.8%, positive predictive value 88.1% and negative predictive value 92.8% for predicting the presence of Staphylococcus aureus in culture (p < 0.001).

CONCLUSIONS

A tracheal aspirate Gram stain can be used to rule out the presence of Staphylococcus aureus in patients with a clinical diagnosis of VAP with a 92.8% Negative Predictive Value. Therefore, 7.2% of patients with Staphylococcus aureus would not be protected by an empiric treatment that limits antimicrobial coverage to Staphylococcus aureus only when Gram positive cocci in clusters are identified.

Endotracheal aspirate and bronchoalveolar lavage fluid analysis: interchangeable diagnostic modalities in suspected ventilator-associated pneumonia?

Authoritative guidelines state that the diagnosis of ventilator-associated pneumonia (VAP) can be established using either endotracheal aspirate (ETA) or bronchoalveolar lavage fluid (BALF) analysis, thereby suggesting that their results are considered to be in accordance. Therefore, the results of ETA Gram staining and semiquantitative cultures were compared to the results from a paired ETA-BALF analysis. Different thresholds for the positivity of ETAs were assessed. This was a prospective study of all patients who underwent bronchoalveolar lavage for suspected VAP in a 27-bed university intensive care unit during an 8-year period. VAP was diagnosed when ≥ 2% of the BALF cells contained intracellular organisms and/or when BALF quantitative culture revealed ≥ 10(4) CFU/ml of potentially pathogenic microorganisms. ETA Gram staining and semiquantitative cultures were compared to the results from paired BALF analysis by Cohen's kappa coefficients. VAP was suspected in 311 patients and diagnosed in 122 (39%) patients. In 288 (93%) patients, the results from the ETA analysis were available for comparison. Depending on the threshold used and the diagnostic modality, VAP incidences varied from 15% to 68%. For the diagnosis of VAP, the most accurate threshold for positivity of ETA semiquantitative cultures was moderate or heavy growth, whereas the optimal threshold for BALF Gram staining was ≥ 1 microorganisms per high power field. The Cohen's kappa coefficients were 0.22, 0.31, and 0.60 for ETA and paired BALF Gram stains, cultures, and BALF Gram stains, respectively. Since the ETA and BALF Gram stains and cultures agreed only fairly, they are probably not interchangeable for diagnosing VAP.

Potentiation effects of amikacin and fosfomycin against selected amikacin-nonsusceptible Gram-negative respiratory tract pathogens

The amikacin-fosfomycin inhalation system (AFIS) is a combination of 2 antibiotics and an in-line nebulizer delivery system that is being developed for adjunctive treatment of pneumonia caused by Gram-negative organisms in patients on mechanical ventilation. AFIS consists of a combination of amikacin and fosfomycin solutions at a 5:2 ratio (amikacin, 3 ml at 100 mg/ml; fosfomycin, 3 ml at 40 mg/ml) and the PARI Investigational eFlow Inline System. In this antibiotic potentiation study, the antimicrobial activities of amikacin and fosfomycin, alone and in a 5:2 combination, were assessed against 62 Gram-negative pathogens from a worldwide antimicrobial surveillance collection (SENTRY). The amikacin MICs for 62 isolates of Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae were ≥32 μg/ml (intermediate or resistant according to the Clinical and Laboratory Standards Institute [CLSI]; resistant according to the European Committee on Antimicrobial Susceptibility Testing [EUCAST]). Each isolate was tested against amikacin (0.25 to 1,024 μg/ml), fosfomycin (0.1 to 409.6 μg/ml), and amikacin-fosfomycin (at a 5:2 ratio) using CLSI reference agar dilution methods. The median MIC values for amikacin and fosfomycin against the 62 isolates each decreased 2-fold with the amikacin-fosfomycin (5:2) combination from that with either antibiotic alone. Interactions between amikacin and fosfomycin differed by isolate and ranged from no detectable interaction to high potentiation. The amikacin-fosfomycin (5:2) combination reduced the amikacin concentration required to inhibit all 62 isolates from >1,024 to ≤ 256 μg/ml and reduced the required fosfomycin concentration from 204.8 to 102.4 μg/ml. These results support continued development of the amikacin-fosfomycin combination for aerosolized administration, where high drug levels can be achieved.

Amikacin-fosfomycin at a five-to-two ratio: characterization of mutation rates in microbial strains causing ventilator-associated pneumonia and interactions with commonly used antibiotics

The amikacin-fosfomycin inhalation system (AFIS), a combination of antibiotics administered with an in-line nebulizer delivery system, is being developed for adjunctive treatment of ventilator-associated pneumonia (VAP). The in vitro characterization of amikacin-fosfomycin (at a 5:2 ratio) described here included determining resistance selection rates for pathogens that are representative of those commonly associated with VAP (including multidrug-resistant strains) and evaluating interactions with antibiotics commonly used intravenously to treat VAP. Spontaneous resistance to amikacin-fosfomycin (5:2) was not observed for most strains tested (n, 10/14). Four strains had spontaneously resistant colonies (frequencies, 4.25 × 10(-8) to 3.47 × 10(-10)), for which amikacin-fosfomycin (5:2) MICs were 2- to 8-fold higher than those for the original strains. After 7 days of serial passage, resistance (>4-fold increase over the baseline MIC) occurred in fewer strains (n, 4/14) passaged in the presence of amikacin-fosfomycin (5:2) than with either amikacin (n, 7/14) or fosfomycin (n, 12/14) alone. Interactions between amikacin-fosfomycin (5:2) and 10 comparator antibiotics in checkerboard testing against 30 different Gram-positive or Gram-negative bacterial strains were synergistic (fractional inhibitory concentration [FIC] index, ≤ 0.5) for 6.7% (n, 10/150) of combinations tested. No antagonism was observed. Synergy was confirmed by time-kill methodology for amikacin-fosfomycin (5:2) plus cefepime (against Escherichia coli), aztreonam (against Pseudomonas aeruginosa), daptomycin (against Enterococcus faecalis), and azithromycin (against Staphylococcus aureus). Amikacin-fosfomycin (5:2) was bactericidal at 4-fold the MIC for 7 strains tested. The reduced incidence of development of resistance to amikacin-fosfomycin (5:2) compared with that for amikacin or fosfomycin alone, and the lack of negative interactions with commonly used intravenous antibiotics, further supports the development of AFIS for the treatment of VAP.

Evaluation of semi-quantitative scoring of Gram staining or semi-quantitative culture for the diagnosis of ventilator-associated pneumonia: a retrospective comparison with quantitative culture

Background

Semi-quantitative Gram stain and culture methods are still commonly used for diagnosing ventilator-associated pneumonia (VAP), due to its convenience. Only a few studies, however, have assessed the reliability of these methods when compared with quantitative cultures, a current standard for the diagnosis of VAP. The objective of this study was to assess the utility of semi-quantitative scores obtained using Gram stains and cultures of endotracheal aspirates when compared with quantitative cultures in the diagnosis of VAP.

Methods

A retrospective chart review of mechanically ventilated patients with clinically suspected VAP in a single intensive care unit was performed. Semi-quantitative scores of Gram stains or culture results were compared with quantitative culture results of endotracheal aspirate for the diagnosis of VAP in 136 samples for 51 patients.

Results

The semi-quantitative scores of Gram stains and the semi-quantitative culture results significantly correlated with the log value of the quantitative culture results (r_s = 0.64 and 0.75). When using a log count ≥6 of quantitative cultures as the reference standard for the diagnosis of VAP, the sensitivity and specificity was 95% and 61% for Gram stain score of ≥1+, and was 42% and 96% for Gram stain score ≥3+, respectively. The sensitivity and specificity was 96% and 40% for the semi-quantitative culture score of ≥2+, and was 59% and 86% for the semi-quantitative culture score of ≥3+, respectively.

Conclusions

Absence of bacteria in semi-quantitative Gram stain and poor growth (≤1+) in semi-quantitative culture method could be utilized to exclude the possibility of VAP, whereas detection of abundant (≥3+) bacteria in semi-quantitative Gram stain could be utilized to strongly suspect VAP.

Is the gram stain useful in the microbiologic diagnosis of VAP? A meta-analysis

In a meta-analysis examining respiratory specimen Gram stain for diagnosis of ventilator-associated pneumonia, absence of bacteria on Gram stain had a high negative predictive value, but a positive Gram stain correlated poorly with organisms recovered in culture. Rapid and accurate diagnosis of ventilator-associated pneumonia (VAP) is a major challenge and no generally accepted gold standard exists for VAP diagnosis. We conducted a meta-analysis to examine the role of respiratory specimen Gram stain to diagnose VAP, and the correlation with final culture results. In 21 studies, pooled sensitivity of Gram stain for VAP was 0.79 (95% confidence interval [CI], .77-0.81; P < .0001) and specificity was 0.75 (95% CI, .73-.78; P < .0001). Negative predictive value of Gram stain for a VAP prevalence of 20%-30% was 91%, suggesting that VAP is unlikely with a negative Gram stain but the positive predictive value of Gram stain was only 40%. Pooled kappa was 0.42 for gram-positive organisms and 0.34 for gram-negative organisms, suggesting fair concordance between organisms on Gram stain and recovery by culture. Therefore, a positive Gram stain should not be used to narrow anti-infective therapy until culture results become available.