Absence of Alveolar Neutrophilia Predictive of Negative Bacterial Pneumonia

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The most common pathogens isolated were <i>Pseudomonas aeruginosa</i>, methicillin-resistant <i>Staphylococcus aureus</i>, and <i>Klebsiella pneumoniae</i>.
The most common pathogens isolated were Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus, and Klebsiella pneumoniae.

Patients undergoing evaluation for ventilator-associated pneumonia who had an alveolar neutrophil percentage <50% had a negative predictive value >90% for bacterial pneumonia, according to the results of a study published in the American Journal of Respiratory and Critical Care Medicine.

Bronchoalveolar lavage specimens from patients undergoing evaluation for ventilator-associated pneumonia at an urban academic medical center were analyzed retrospectively for associations between alveolar neutrophilia and bacterial pneumonia diagnosis. All lavage samples were processed for flow-cytometry sorting within 12 hours of collection. Pneumonia was defined as ≥104 colony-forming units/mL of a bacterial species on quantitative culture in the setting of a clinical suspicion of infection and an abnormal chest radiograph.

Of the 1156 bronchoalveolar lavage specimens screened for inclusion, 851 were included in the final analysis. Of these 851 specimens, 344 (40.4%) met the definition for bacterial pneumonia. The most common pathogens isolated were Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus, and Klebsiella pneumoniae. The area under the curve for bronchoalveolar lavage neutrophilia was 0.751 (95% CI, 0.719-0.784). When bronchoalveolar lavage neutrophils were <50%, the negative predictive value for pneumonia was 91.5%.

“[T]he absence of alveolar neutrophilia is useful in ruling out bacterial pneumonia in mechanically ventilated patients with suspected infection,” the researchers concluded. “A combination of cellular and molecular analysis of the host and pathogen in [bronchoalveolar lavage] fluid shows promise for improving the diagnosis and management of pneumonia.”

Reference

Walter J, Ren Z, Yacoub T, et al. Multidimensional assessment of the host response in mechanically ventilated patients with suspected pneumonia [published online November 6, 2018]. Am J Respir Crit Care Med. doi:10.1164/rccm.201804-0650OC

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