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

AIMS: 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. METHODS AND RESULTS: 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. CONCLUSIONS: 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. SIGNIFICANCE AND IMPACT OF THE STUDY: 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.