Detection of the etiological agents of hospital-acquired pneumonia - validity and comparison of different types of biological sample collection: a prospective, observational study in intensive care patients

Background: There is still a lack of evidence as to which method of biological sample collection is optimal for identifying bacterial pathogens causing hospital-acquired pneumonia (HAP). Much effort has been made to find an easy and valid approach to be used in clinical practice. Methods: The primary endpoint of this prospective, observational study was to determine the predictive value of oropharyngeal swab (OS) and gastric aspiration (GA) as simple and non-invasive methods for diagnosing HAP. Their efficacy was compared to endotracheal aspiration (ETA) and protected specimen brushing (PSB), the standard methods approved for HAP diagnosis. Results: Initially, 56 patients were enrolled. Significant amounts of bacterial pathogens were detected in 48 patients (79 isolates) in Round A and in 39 patients (45 isolates) in Round B (after 72 hours). The sensitivity rates were: ETA 98%, PSB 31%, OS 64% and GA 67% in Round A and ETA 87%, PSB 32%, OS 74% and GA 42% in Round B. Strains of 12 bacterial species were identified in the samples. The three most common etiological agents (both rounds together) were Klebsiella pneumoniae (23.7%), Burkholderia multivorans (21.1%) and Pseudomonas aeruginosa (15.8%). Conclusions: Blind ETA is an optimum method for obtaining biological samples for identification of etiological agents causing HAP in intubated patients. Microbial etiological agents were more frequently detected in ETA samples than in those collected by PSB. If ETA/PSB results are negative, samples may be collected by OS and/or GA as these techniques followed ETA in terms of the frequency of pathogen detection.