Transfer of dry surface biofilm in the healthcare environment: the role of healthcare workers' hands as vehicles

Background: Dry surface biofilms (DSBs) persist for extended periods in hospital, and may play a significant role in transmission of healthcare-associated infections. Aim: To determine whether DSBs may be transferred from hospital surfaces to healthcare workers' hands. Method: Twelve-day Staphylococcus aureus DSB was grown on polycarbonate and glass coupons in a CDC Biofilm Reactor^®. A total of 1.8 × 10⁶ and 8.8 × 10⁵ bacteria grew on the polycarbonate and glass coupons respectively. Transmission was tested by lifting the coupon with forefinger and thumb of ungloved hands to a height of 30 cm, then touching horse blood agar (HBA) plates 19 sequential times. Transferred bacterial number was determined by colony-forming units. The effect of DSB wetting on biofilm transfer was tested with 5% neutral detergent treatment for 5 s. Findings: Between 5.5 and 6.6% of the DSB bacteria were transferred to hands with one touch and ∼20% were then transferred to HBA with one touch, giving an overall transfer rate of 1.26% and 1.04% for polycarbonate and glass coupons, respectively. Detergent treatment had little effect on bacterial removal from coupons, but, for biofilm grown on polycarbonate, significantly increased transferral to HBA (P < 0.001) to 5.2%. Large numbers of bacteria were transferred by bare hands to multiple fomites. One-third of polycarbonate coupons transferred >1000 colonies during the first five sequential touches. Sufficient bacteria to cause infection were transmitted up to 19 times following one touch of the DSB. Conclusion: DSB bacteria are transferred by hands from one fomite to multiple fomites, suggesting that DSB may serve as a persistent environmental source of pathogens.