Swab-based recovery of simethicone emulsion at different concentrations in gastroscope biopsy channels: an experimental study

Simethicone is widely used during endoscopy but raises concerns about residue retention. This study quantitatively evaluated swab-recoverable simethicone residues in endoscope channels under clean and contaminated conditions, and assessed standard reprocessing effectiveness. Thirty-six gastroscopes with nominal 2.8-mm instrument channels were divided into clean (Olympus GIF-HQ290, n = 18) and contaminated (SonoScape 580, n = 18) arms. Three simethicone concentrations (0.1, 0.2, 1.0 mg/mL) were tested. The contaminated arm received defibrinated sheep blood containing Escherichia coli (10⁶ CFU/mL) before simethicone. Residues were measured by ¹H-nuclear magnetic resonance before and after standard reprocessing (manual cleaning plus automated orthophthalaldehyde disinfection). A linear mixed-effects model (LMM) was fitted to log-transformed residue mass with arm, phase, concentration, and their interactions as fixed effects, and endoscope as a random intercept. In clean endoscopes, pre-reprocessing swab-recoverable residue increased with concentration (F = 12.842, P < 0.001), decreasing significantly after reprocessing to 0.22–0.33 mg (P < 0.001). In contaminated endoscopes, no concentration-response relationship was observed, and residues did not decrease significantly after reprocessing (P = 0.134). A linear mixed-effects model confirmed that the pre-to-post reduction in residue differed significantly between clean and contaminated endoscopes (arm × phase interaction: coefficient = 0.597, 95% CI: 0.092 to 1.102, P = 0.021). ​Residues did not decrease significantly in the contaminated arm (P = 0.134), although this comparison had only 32.3% statistical power. Standard reprocessing effectively reduced swab-recoverable simethicone residue in clean endoscopes. The pre-to-post change differed between the two study arms; however, because endoscope model and contamination condition were collinear, this difference cannot be attributed exclusively to biological contamination. Whether standard reprocessing definitively fails in soiled endoscopes remains inconclusive and warrants larger model-controlled studies using validated absolute-quantification methods. Even low-dose simethicone (0.1 mg/mL) leaves detectable swab-recoverable residue in endoscope biopsy channels after standard reprocessing. Standard reprocessing significantly reduces swab-recoverable simethicone residue in clean endoscopes (58.1% reduction, P < 0.001). The pre-to-post change in swab-recoverable residue differed between study arms (LMM arm × phase interaction, P = 0.021), but biological-soil and endoscope-model effects cannot be separated; within-arm effectiveness in contaminated scopes remains inconclusive (P = 0.134, power 32.3%). This study quantifies the swab-based recovery of simethicone residue, not the absolute residual mass on the channel wall; reported values represent the recoverable fraction under standardized sampling conditions.