Preliminary Study on the Clinical Application Value of "Showering Cells" in Diagnosing Aspiration Pneumonia

Study Design and Participants: This single-center, retrospective case-control study enrolled adult patients (18-100 years) hospitalized in the RICU of the Chinese PLA General Hospital between January 2018 and December 2024, who were clinically diagnosed with pulmonary infection and underwent both bronchoalveolar lavage (BAL) and rapid on-site evaluation (ROSE) examination. Exclusion criteria included age outside the range, non-infectious pulmonary diseases, absence of bronchoscopy/BAL, unqualified ROSE specimens (poor image quality or substandard samples), or missing critical clinical data for grouping. Diagnostic Criteria and Grouping: Aspiration pneumonia (AP) was diagnosed using a clinical-imaging composite gold standard. The AP group had to simultaneously meet: (1) chest CT showing new gravitationally-dependent infiltrates; (2) a definite aspiration history or at least one high-risk factor (e.g., impaired consciousness, swallowing dysfunction, gastroesophageal reflux, diminished cough/gag reflex, poor oral hygiene); and (3) ≥2 of the following infection criteria: fever (\>38.0°C or \<36.0°C), new/worsened respiratory symptoms or purulent secretions with gastric contents, and abnormal peripheral white blood cell count or left shift. The non-AP group comprised patients with ≥2 infection criteria but who did not meet the AP diagnostic criteria. ROSE Procedure and Definition of "Showering Cells": BALF was submitted for testing within 30 minutes, centrifuged, and the sediment smeared onto slides for Gram and Diff-staining. A blinded morphologist assessed specimen adequacy and performed microscopic examination. "Showering cells" were defined as squamous epithelial cells observed under high-power fields (×1000) with the distinct morphology of no bacterial adhesion on the surface, clear cytoplasm, and a clean background. Ten non-overlapping high-power fields were randomly selected to count the total number of showering cells and total squamous epithelial cells, and th