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Assessing the Likelihood of Hand-to-Hand Cross-Transmission of Bacteria: An Experimental Study

  • Fernando Bellissimo-Rodrigues (a1) (a2), Daniela Pires (a1) (a3), Hervé Soule (a1), Angèle Gayet-Ageron (a1) and Didier Pittet (a1)...

Although the hands of healthcare workers (HCWs) are implicated in most episodes of healthcare-associated infections, the correlation between hand contamination and the likelihood of cross-transmission remains unknown.


We conducted a laboratory-based study involving pairs of HCWs. The hands of a HCW (transmitter) were contaminated with Escherichia coli ATCC 10536 before holding hands with another HCW (host) for 1 minute. Meanwhile, the unheld hand of the transmitter was sampled. Afterward, the host’s held hand was also sampled. Each experiment consisted of 4 trials with increasing concentrations of E. coli (103–106 colony-forming units [cfu]/mL). The primary outcome was the likelihood of transmission of at least 1 cfu from transmitter to host. We used a mixed logistic regression model with a random effect on the subject to assess the association between transmission and bacterial count on the transmitter’s hands.


In total, 6 HCWs performed 30 experiments and 120 trials. The bacterial counts recovered from host hands were directly associated with the bacterial counts on transmitter hands (P<.001). The probability of cross-transmission was 8.22 higher (95% confidence interval [CI], 0.98–68.8) when transmitter hand bacterial count was >1 and ≤3 log10 cfu compared to ≤1 log10. When transmitter contamination was <1 log10 cfu, no cross-transmission was detected.


There is a direct relationship between the bacterial burden on HCWs hands and the likelihood of cross-transmission. Under the described conditions, at least 1 log10 cfu must be present on HCW hands to be potentially transmitted. Further studies are needed at the low contamination range.

Infect Control Hosp Epidemiol 2017;38:553–558

Corresponding author
Address correspondence to Professor Didier Pittet, MD, MS, Infection Control Programme and WHO Collaborating Centre on Patient Safety, University of Geneva Hospitals and Faculty of Medicine, 4 Rue Gabrielle-Perret-Gentil, 1211, Geneva, Switzerland (
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Authors of equal contribution.

PREVIOUS PRESENTATION: These data were presented in part (no. 2016-A-2528) at the American Society of Microbiology (ASM) Microbe 2016 Congress in Boston, Massachusetts, on the June 18, 2016.

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