Molecular versus conventional assay for diagnosis of hospital-acquired pneumonia in critically ill patients: a single center experience

Purpose

Lower respiratory tract infections are reported as one of top five causes of mortality and morbidity in the world. A bacterial etiology is often involved in HAP, most frequently from multidrug resistant gram-negative bacteria, and fast accurate diagnosis of etiologic agent(s) of LRTI is essential for an appropriate management. The aim of this retrospective study was to evaluate the analytical performance of Biofire Filmarray Pneumonia Plus for bacteria detection in bronchoalveolar lavage samples and the concordance of bacterial loads between BFPP and cultural gold standard methods.

Methods

A total of 111 BAL samples were obtained from 111 consecutive patients admitted to Intensive Care Unit of “Renato Dulbecco” Teaching Hospital of Catanzaro, from March 2023 to March 2024.

Results

Compared to conventional methods, BFPP showed a sensitivity of 99 % and a specificity of 64 %. The agreement between the two methods was assessed by calculating PPA and NPA, being 89 % and 95 %, respectively. The most common bacterial species identified at BFPP was Klebsiella pneumoniae, followed by Acinetobacter calcaceuticus-baumanii complex, Staphylococcus aureus and Pseudomonas aeruginosa. Bacterial load (CFU/ml) in relation to copy number detected by molecular analysis showed the best performance for value ≥10⁶ copie/mL. About molecular mechanisms of resistance in comparison to phenotypic profiles, the highest level of performance was observed for presence of KPC genes, all isolates showing resistance to carbapenems, followed by OXA-48 like and NDM.

Conclusion

The high concordance reported in this study between the identification of resistance genes and phenotypic indication can lead to an appropriate, fast and tailored antibiotic therapy.