Comparative surface-to-hand and fingertip-to-mouth transfer efficiency of gram-positive bacteria, gram-negative bacteria, and phage

Abstract

Aims: To determine the transfer efficiency of micro-organisms from fomites to hands and the subsequent transfer from the fingertip to the lip. Methods and Results: Volunteers hands were sampled after the normal usage of fomites seeded with a pooled culture of a Gram-positive bacterium (Micrococcus luteus), a Gram-negative bacterium (Serratia rubidea) and phage PRD-1 (Period A). Activities included wringing out a dishcloth/sponge, turning on/off a kitchen faucet, cutting up a carrot, making hamburger patties, holding a phone receiver, and removing laundry from the washing machine. Transfer efficiencies were 38·47% to 65·80% and 27·59% to 40·03% for the phone receiver and faucet, respectively. Transfer efficiencies from porous fomites were <0·01%. In most cases, M.luteus was transferred most efficiently, followed by phage PRD-1 and S. rubidea. When the volunteers' fingertips were inoculated with the pooled organisms and held to the lip area (Period B), transfer rates of 40·99%, 33·97%, and 33·90% occurred with M. luteus, S. rubidea, and PRD-1, respectively. Conclusions: The highest bacteral transfer rates from fomites to the hands were seen with the hard, non-porous surfaces. Even with low transfer rates, the numbers of bacteria transferred to the hands were still high (up to 106 cells). Transfer of bacteria from the fingertip to the lip is similar to that observed from hard surfaces to hands. Significance and Impact of the Study: Infectious doses of pathogens may be transferred to the mouth after handling an everyday contaminated household object.