New sequential-touch method to determine bacterial contact transfer rate from finger to surface

Infection can occur via surface touch. A new method was developed to more accurately evaluate the bacterial transfer rate from a finger to a surface.

Staphylococcus aureus was used as the model bacteria to inoculate a thumb. Sequential touches were made between the contaminated thumb and a series of clean microscope slides. The bacteria on the glass surface were cultured in situ, and the bacterial transfer rate was evaluated by fitting the colony-forming units (CFUs) on glass surfaces with the exponential decay function. The resident microflora on thumb were also used to validate the new method.

The average transfer rate was 12·9% for S. aureus under the baseline condition. The CFUs counted on the glass surfaces were well fitted by the exponential decay function. A set of trials with more surfaces resulted in a more accurate evaluation. No statistically significant difference was found in the estimated transfer rate between the standard strain and the resident microflora.

The new method significantly increases the accuracy of evaluation of the microbial transfer rate from a finger to a surface while maintaining a low workload.