Effect of surgical mask position on bacterial contamination of the operative field

The influence of surgical mask usage on bacterial contamination of the operative field was studied during 30 cardiac catheterization procedures. Mask position was varied during each procedure according to a predesigned random table. The number of bacterial colonies recoverable when no mask was worn was significantly higher than that detected when a full mask was worn (P < 0·002). Shedding of Staphylococcus epidermidis was greater when no mask was worn (mean 5·2 colonies 10 min^-1) than shedding with full mask (mean 2·7 colonies 10 min^-1; P < 0·004). Although mask placement below the nose was associated with higher mean colony counts than that above the nose, these differences were not statistically significant.