Measuring bi-directional bacterial transfer efficiencies and the impact on model parameterization

Healthcare-associated infections (HAIs) affect millions of patients every year globally. Implementation of improved infection control and surveillance methods have led to a reduction in HAIs, but the incidence remains high. Pathogen transmission via environmental surfaces (fomites) and healthcare workers (HCW) contribute to the persistence of HAIs in hospitals. A critical parameter needed to assess risk due to environmental transmission is the transfer efficiencies of pathogens from fingers to fomites and fomites to fingers. Most fate and transport mathematical models assume equal transfer efficiency values for calculating the pick-up rate and the deposit rate of pathogens. This assumption may be appropriate when the two contacting surfaces are composed of the same material (i.e. skin-skin contact). However, when the two contacting surfaces are different (i.e. skin-fomite contact), this assumption may not hold.

We found that the overall pick-up transfer efficiency of A. baumannii was significantly higher than the deposit transfer efficiency, regardless of glove use. We used this data to evaluate how the commonly-used assumption of symmetry in transfer efficiencies changes the dynamics of pathogen movement between patients and rooms and the exposures to uncolonized patients.

Symmetric models consistently overestimate A. baumannii contamination levels on fomites and underestimate contamination on patients and HCWs compared to the asymmetrical model. The magnitudes of these miscalculations can exceed 100% and extend to biased effectiveness estimates for hand washing interventions. To provide more accurate models that can inform control strategies, additional bidirectional transfer studies are needed across different pathogens and surface types.