Physical factors that affect microbial transfer during surface touch

Knowledge of the factors that affect microbial transfer during surface touch is essential for controlling the risk of infection by fomite transmission. Thirteen factors that affect the microbial transfer rate were identified by reviewing the published data. Principal component analysis was performed. Stepwise multiple linear regression revealed donor wetness, microbial transfer direction, donor roughness and existence of rubbing to be the most significant factors. The transfer rate during surface touch was newly measured using a purpose-made touch machine. The microbial transfer rate was quantified by polymerase chain reaction. In addition to the four significant factors determined by data analysis, five other factors were investigated, including three that have received wide attention (surface material, bacterial species and touch force) and two that were recently found to be significant (bacterial suspension medium and bacterial growth phase). The relative standard deviation of the measured transfer rate was reduced to 35.6%. The average metal-to-fingerpad transfer rate of Staphylococcus aureus was 15.6% in the baseline condition. It increased to more than 35% under positive conditions such as rubbing during the touch and decreased to less than 5% when water was used as the bacterial suspension medium. Furthermore, the transfer rate increased with a decrease in the donor roughness or an increase in the touch force. No significant difference was observed when the metal surface was replaced with glass and quartz or between the S. aureus and Escherichia coli experiments. These results offer insights into the factors that affect microbial transfer during surface touch.