The usefulness of filmarray as a diagnostic method for bacterial pneumonia

Introduction: Early diagnosis of severe pneumonia and appropriate treatment is related to improved survival. The Film Array is a matrix in which the most common pathogens related to community and nosocomial pneumonia are analyzed through PCR. It has been shown to be a valid tool for early diagnosis, although its validity compared to culture (gold standard) is not yet well defined. Objectives: -Explore the effectiveness of the Film Array as an early diagnostic tool for severe pneumonia versus conventional respiratory secretion culture (gold standard). -Establish a cut-off point for a positive Film Array (cycles) and culture isolation. Methods: A retrospective descriptive study was conducted based on lower respiratory tract cultures (BAS, BAL, CTT) obtained from patients with suspected pneumonia on mechanical ventilation who underwent respiratory Filmarray testing between January 2022-March 2023. The presence of legionella and pneumococcus antigenuria was also considered equivalent to positive culture. Multiplex PCR (Filmarray® BioFire- A Biomérieux Company) was used for the Film Array. The pneumonia criteria were based: Presence or progression of infiltrate reasonably excluding cardiac insufficiency or hypervolemia. Associated with at least one of the following variables: fever > 38 °C without other origin, leukopenia (< 4,000/mm3) or leukocytosis (≥ 12,000/mm3), as well as at least one of the following variables: Purulent sputum, cough dyspnea or tachypnea, suggestive pulmonary auscultation and worsening gas exchange. Results: A total of 74 samples were identified, of which 10 were discarded due to insufficient sample, exclusion of infection or dissociation between the Filmarray and culture samples. 64 samples were included for analysis, of which 24 (37.5%) were positive by culture. The Filmarray test was positive in 19 of the 24 culture-positive cases (79%) and in 6 of the 40 culture-negative cases (15%). Equivalence between the microbiological results obtained by culture and the bacterial pathogens identified by the Filmarray was compared using a contingency table, evaluating positive and negative predictive values (Chi square p < 0.001, positive predictive value 76%, negative predictive value 87.2%, sensitivity 79.2%, and specificity 85%. Accuracy of 82.8%) as well as the Kappa index (Kappa 0.636, 95% CI 0.39-0.88). The appearance of the germ in cultures was analyzed with respect to the cycles present in the Filmarray, evaluating the cutoff point for culture isolation. A cutoff point of 10∧5 cycles was found for appearance on the culture plate (Significance of Montecarlo (bilateral) p 0.002; 99% CI 0.001-0.003). Conclusions: The Film array has proven to be a highly valid tool for early etiological diagnosis of severe bacterial pneumonia, with high equivalence to cultures. The germs that did not appear on the Filmarray were due to their absence in the matrix, mainly opportunistic, so its use in immunocompromised patients should be interpreted with caution. (Table Presented).