Effect of a Modified Air-Gun Purging Method on Microbial Detection of Endoscope Drying Air: A Comparative Study

To compare conventional direct blowing with a modified acrylic-shielded air-gun purging method for microbiological detection of endoscope drying air.

From April to June 2024, seven endoscope drying air guns connected to the same centralized compressed-air system underwent five paired sampling rounds using both methods, producing 35 samples per method. Direct blowing exposed a nutrient agar plate to discharged air in the room, whereas the modified method placed the plate inside an acrylic shield to create a relatively enclosed sampling space. Colony-forming units (CFU) were quantified, and representative colonies were identified.

Direct blowing yielded positive cultures in 34 of 35 samples (97.1%), whereas all 35 samples collected with the modified method were negative (exact McNemar P<0.001). Direct-blowing counts ranged from 0 to 16 CFU/plate, with a median of 5 CFU/plate (IQR, 3-8) and a mean of 6.1 ± 3.9 CFU/plate; the modified method yielded 0 CFU/plate in every sample. Among 41 representative isolates from positive direct-blowing cultures, 25 (61.0%) were Staphylococcus hominis, 9 (22.0%) Aspergillus fumigatus, and 7 (17.1%) Kocuria palustris. No typical high-concern waterborne or enteric Gram-negative organisms were identified among the representative isolates.

The modified air-gun purging method markedly reduced microbial recovery associated with open environmental exposure and may better isolate discharged drying air from ambient interference. This simple, low-cost approach may support more specific microbiological surveillance of endoscope drying-air guns, although broader validation is required before standardization.