Abstract
Effective hand drying is an important part of hand hygiene that can reduce the risk of infectious disease transmission through cross-contamination of surfaces by wet hands. However, hand drying methods may also cause aerosolisation of pathogenic microorganisms if they are present in washed hands. This study investigated experimentally the impact of washing hands and different hand drying methods on the concentration and size distribution of aerosols and bacteria in indoor air. In this experiment, aerosol and bacteria concentrations were measured in indoor air while volunteers rinsed their hands with water or washed with soap and water prior to drying them with paper towels or jet air dryers. Results showed that the concentration of aerosols and bacteria in air increased with people walking in the room and washing hands, with a further increase during the hand drying process. The concentration of aerosols decreased with particle size, with maximum concentrations after drying hands of 6.63 × 106 ± 6.49 × 105 and 2.28 × 104 ± 9.72 × 103 particles m−3 for sizes 0.3 to <0.5 and ≥5.0 μm, respectively. The concentration of bacteria in indoor air after drying hands increased to a maximum of 3.81 × 102 ± 1.48 × 102 CFU m−3 (jet air dryers) and 4.50 × 102 ± 4.35 × 101 CFU m−3 (paper towels). This study indicates that the increase of aerosols and bacteria in air after drying hands with jet air dryers or paper towels are comparable and not statistically different from concentrations associated with walking and washing hands in the same environment. This work can support the development of hand hygiene practices and guidelines for public washrooms.
Highlights
Human skin, in particular hands, harbors resident and transient microorganisms, which may include bacteria, viruses and fungi
The background concentration of bacteria varied between 9.63 ± 0.00 and 1.21 x 102 ± 4.90 x 101 colony forming units (CFU) m−3
Concentration of aerosols and bacteria were measured when volunteers only walked in the chamber and when volunteers walked and washed hands, but did not dry them
Summary
In particular hands, harbors resident and transient microorganisms, which may include bacteria, viruses and fungi. Resident microorganisms are part of human skin flora, typically are not pathogenic and play a positive role in people’s health [1, 2]. Some transient microorganisms are innocuous to people, others might be pathogenic and can transmit disease [1, 2]. Effective hand washing can remove transient microorganisms, playing an important role in preventing disease transmission. Epidemiological studies have demonstrated that regular and adequate hand washing with soap and water can reduce the incidence of diarrhea, upper respiratory illness and other infectious diseases [3–5]. Health organizations worldwide recommend frequent hand washing with soap and water followed by drying, or the use of disinfectant solutions, such as alcohol gels [6, 7]
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