ASM Microbe
ASM Microbe
June 21, 2016
2 min read

Alcohol-based hand hygiene confers no additional benefit after 30 seconds

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BOSTON — Although the effectiveness of alcohol-based handrub increases with duration, practicing WHO’s suggested technique for longer than 30 seconds may not confer any additional sanitation benefits, according to experimental data presented here at ASM Microbe 2016.

Furthermore, a separate study quantifying the spread of Escherichia coli between health care workers’ hands suggests a direct relationship between bacterial load and the risk for bacterial spread. According to Fernando Bellissimo-Rodrigues, MD, PhD, research fellow at the University of Geneva Hospitals, these findings reinforce the importance of reducing skin contamination.

Handrub for 45, 60 seconds appears unnecessary

While many studies have examined hand hygiene compliance and techniques to maximize friction, Daniela Pires, MD, also from the University of Geneva Hospitals, said little is known about how long a health care worker should spend performing hand hygiene. To address this gap, Pires, Bellissimo-Rodriguez and colleagues contaminated the hands of 23 health care workers (HCWs) with E. coli, and instructed these HCWs to rub for 10, 15, 20, 30, 45 and 60 seconds. All participants cleansed with 3 mL of isopropanol 60% solution, and adhered to WHO’s “how to handrub” technique. The researchers collected fingertip bacterial counts before and after rubbing, and employed a linear analytic model to measure the effectiveness of each duration.

After adjustment for participants’ gender and hand size, data from 110 measurements indicated a significant trend of steadily decreasing bacterial counts with increased cleansing duration (P < .001). However, Pires said the adjusted decline in bacterial count after 45 seconds of rubbing was significantly smaller than declines measured at 15, 20 and 30 seconds, as was the difference after 60 seconds of rubbing compared with 20 or 30 seconds.

“From our data, there doesn’t seem to be a gain from [performing] hand hygiene for longer than 30 seconds,” Pires said during the presentation. “But of course, more studies are needed to assess this in the clinical setting.”

Greater contamination increases risk for transmission

Although hand hygiene reduces bacterial load, Bellissimo-Rodrigues said the minimal quantity required for skin-to-skin transmission between HCWs has been unclear. In a second experimental design study, the researchers contaminated the hands of six HCWs using suspensions with E. coli concentrations ranging from 103 cfu/mL to 106 cfu/mL. Participants with a contaminated hand were then instructed to hold the hand of another participant for 1 minute with their fingers interlocked to simulate skin-to-skin contact. The researchers collected cultures from the recipient’s fingertips, and used these to model bacterial transmissions resulting from each test. 

The researchers reported a positive relationship between the bacterial counts of the contaminator and the recipient (P < .001). Compared with inoculum less than 3 log10, risk of cross-contamination increased more than fourfold with inoculum between 3 log10 and 3.5 log10, more than 16-fold with inoculum between 3.5 log10 and 4 log10, and nearly 47-fold with more than 4 log10. They observed no cross-contamination events until the bacterial count of the contaminator’s hand exceeded 1 log10.

“Under the described conditions, at least 1 log10 of E. coli must be present on HCWs’ hands to be potentially transmitted,” Bellissimo-Rodrigues said. “This threshold might be useful for further developing the microbiological concept of ‘safe hands.’ ” — by Dave Muoio


Bellissimo-Rodrigues F, et al. Assessing the Risk of Hand-to-Hand Transmission of Bacteria. Presented at: ASM Microbe; June 16-20, 2016; Boston.

Pires D, et al. Hand Hygiene with Alcohol-Based Handrub: How Long is Long Enough? Presented at: ASM Microbe; June 16-20, 2016; Boston.

Disclosure: The researchers report no relevant financial disclosures.