Impact of the microscopic quality of endotracheal aspirates on the performance of the Filmarray® pneumonia plus panel in intensive care unit patients with suspected lower respiratory tract infection

We investigated how the microscopic quality of endotracheal aspirates (ETA) impacts the performance of the Filmarray® pneumonia plus panel (FA-PP) in patients undergoing mechanical ventilation (IMV) with suspicion of lower respiratory tract bacterial infection (LRTBI).

The quality of ETA was categorized according to the number of leukocytes and buccal squamous epithelial (BSE)/field (100x magnification). G5 (< 10 BSE cells and > 25 leukocytes/field) and G4 (10–25 BSE cells and > 25 leukocytes/field) ETA were tested in parallel by the FA-PP and conventional semiquantitative culture.

In total, 153 ETA were graded as G5 (from 115 patients) and 56 as G4 (from 48 patients). Focusing on “conventional” bacterial species, a trend towards more positive results (P = 0.16), and co-detections (P = 0.18) was returned by G5 ETA. Although more targets were detected on G5 ETA (P = 0.005), the spectra of bacteria detected was comparable across G5 and G4 specimens. A trend towards higher bacterial burdens as quantitated by the FA-PP, and irrespective of the target, was observed in G5 (median, 10⁶ genome copies/ml) vs. G4 ETA (median, 10⁵ genome copies/ml). The degree of full agreement between FA-PP and culture was higher for G5 ETA (Kappa value, 0.54; 95% CI, 0.43–0.66) than for G4 ETA (Kappa value, 0.31; 95% CI, 0.11–0.49). For all bacterial targets detected, genome copy/ml numbers exceeded colony forming units (CFU)/ml counts in 1–2 log₁₀, irrespective of ETA grading. The degree of correlation between genome copies/ml and CFU/ml was slightly better for G5 ETA (Rho = 0.65; P = 0.001) than for G4 ETA (Rho = 0.54; P = 0.11).

FA-PP testing of G5 ETA may provide more comprehensive and clinically useful information compared with G4 specimens in patients undergoing IMV with suspected LRTBI and receiving antimicrobial therapy. Yet G4 ETA may still provide useful microbiological information.