Minding the matrix: The importance of inoculum suspensions on finger transfer efficiency of virus

AIMS: The aim of this study was to determine how the transfer efficiency of MS‐2 coliphage from the toilet seat to hands and fingertip to lip differs according to the suspension of the inoculum. METHODS AND RESULTS: Hands were sampled after lifting a toilet seat which was inoculated with MS‐2 on the underneath side. MS‐2 was suspended in a spectrum of proteinaceous and non‐proteinaceous solutions. Transfer efficiencies were greatest with the ASTM tripartite soil load (3.02% ± 4.03) and lowest with phosphate‐buffered saline (PBS) (1.10% ± 0.81) for hand‐to‐toilet seat contacts. Finger‐to‐lip transfer rates were significantly different (p < 0.05) depending on suspension matrix, with PBS yielding the highest transfer (52.53% ± 4.48%) and tryptose soy broth (TSB) the lowest (23.15% ± 24.27%). Quantitative microbial risk assessment was used to estimate the probability of infection from adenovirus and norovirus from finger contact with a toilet seat. CONCLUSIONS: The greatest transfer as well as the largest variation of transfer were measured for finger‐to‐lip contacts as opposed to toilet seat‐to‐finger contacts. These factors influence the estimation of the probability of infection from micro‐activity, that is, toilet seat adjustment. SIGNIFICANCE AND IMPACT: Viruses may be transferred from various human excreta with differing transfer efficiencies, depending on the protein content.