Bacterial contamination of mask inner surfaces during prolonged use by paramedics in prehospital emergency care

Paramedics are routinely exposed to respiratory secretions and aerosols in prehospital settings, necessitating prolonged or repeated mask use for infection prevention. However, evidence regarding time-dependent bacterial contamination of masks worn during extended prehospital duty remains limited. This within-subject repeated-measures study investigated bacterial contamination on the inner surface of KF94 masks worn by 24 Korean paramedics during routine duty. Mask samples were collected after 6, 12, and 24 h of wear. Bacterial contamination was quantified using colony-forming unit (CFU) counts, and bacterial species were identified via 16S rRNA gene sequencing. Differences across time points were analyzed using repeated-measures analysis of variance. Written informed consent was obtained from all participants, and institutional permission was secured from participating EMS agencies. Bacterial contamination increased significantly with prolonged mask-wearing duration (F(2,46) = 22.94, p < 0.001, partial η²=0.50). Mean CFU counts increased from 134.64 ± 131.30 CFU/mL at 6 h to 595.25 ± 153.23 CFU/mL at 24 h, approximately a 4.4-fold increase. Gram-positive bacteria predominated, including species from the Bacillaceae, Staphylococcaceae, and Micrococcaceae families. Attitudes toward mask use were positive overall (mean 3.89/5), alongside moderate perceived discomfort during prolonged wear. Prolonged mask use among paramedics is associated with significant, time-dependent bacterial accumulation on the inner surface of masks. These findings provide preliminary evidence that may inform the development of occupation-specific, evidence-based guidelines on mask replacement and PPE management in prehospital emergency care.