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Journal of Hospital Infection xxx (2014) 1e8
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Journal of Hospital Infection
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Microbiological comparison of hand-drying methods:
the potential for contamination of the environment,
user, and bystander
E.L. Best a, P. Parnell a, M.H. Wilcox a, b, *
a
b
Microbiology Department, Old Medical School, Leeds General Infirmary, Leeds Teaching Hospitals NHS Trust, Leeds, UK
University of Leeds, Leeds, UK
A R T I C L E
I N F O
Article history:
Received 27 November 2013
Accepted 7 August 2014
Available online xxx
Keywords:
Air driers
Bacteria
Droplet dispersal
Environmental contamination
Hand drying
Hand hygiene
S U M M A R Y
Background: The efficiency of hand drying is important in preventing pathogen spread,
but knowledge surrounding which drying methods contribute least towards contamination
of the environment and users is limited.
Aim: To compare the propensity of three common hand-drying methods (jet air, warm air
dryers, and paper towels) to contaminate the environment, users, and bystanders.
Methods: Hands were coated in lactobacilli to simulate poorly washed, contaminated
hands, and dried. The investigation comprised 120 air-sampling tests (60 tests and 60
controls), divided into close and 1 m proximity from the drying process. Separate tests
used hands coated in paint to visualize droplet dispersal.
Findings: Air bacterial counts in close proximity to hand drying were 4.5-fold higher for
the jet air dryer (70.7 cfu) compared with the warm air dryer (15.7 cfu) (P ¼ 0.001), and
27-fold higher compared with use of paper towels (2.6 cfu) (P < 0.001). Airborne counts
were also significantly different during use of towel drying versus warm air dryer
(P ¼ 0.001). A similar pattern was seen for bacterial counts at 1 m away. Visualization
experiments demonstrated that the jet air dryer caused the most droplet dispersal.
Conclusion: Jet air and warm air dryers result in increased bacterial aerosolization when
drying hands. These results suggest that air dryers may be unsuitable for use in healthcare
settings, as they may facilitate microbial cross-contamination via airborne dissemination
to the environment or bathroom visitors.
ª 2014 The Healthcare Infection Society. Published by Elsevier Ltd. All rights reserved.
Introduction
Hand hygiene is a fundamental component for controlling
the spread of infection.1,2 Promotion of improved hand hygiene
* Corresponding author. Address: Microbiology Department, Old
Medical School, Leeds General Infirmary, Leeds Teaching Hospitals NHS
Trust, Leeds LS1 3EX, UK. Tel.: þ44 113 392 6818; fax: þ44 113 392
2696.
E-mail address: [email protected] (M.H. Wilcox).
is recognized as an important public health measure. There is
much emphasis on the correct method for handwashing, but
less so concerning the options for drying hands. Evidence suggests that efficiency of hand drying is important in the prevention of the transfer of micro-organisms from person to
person or to the environment.3 However, the risk of aerosolizing micro-organisms during hand drying by various methods
remains unclear.
Methods for hand drying vary widely and include paper or
cloth towels, warm air dryers or jet air dryers either singly or in
http://dx.doi.org/10.1016/j.jhin.2014.08.002
0195-6701/ª 2014 The Healthcare Infection Society. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Best EL, et al., Microbiological comparison of hand-drying methods: the potential for contamination of the
environment, user, and bystander, Journal of Hospital Infection (2014), http://dx.doi.org/10.1016/j.jhin.2014.08.002
2
E.L. Best et al. / Journal of Hospital Infection xxx (2014) 1e8
airborne bacteria. Experiments were carried out over a period
of six weeks.
combination. Drying with towels may remove remaining microorganisms through friction, while moisture is wicked away into
the absorbent material. Warm air dryers evaporate moisture
and remove some micro-organisms during hand rubbing,
although this process may take too long for efficient use, with
hands consequently remaining damp. Newer jet air dryers rely
on the passage of high speed, usually unheated, air to dry
hands without rubbing, typically in 15 s.4 The selection of
drying method may depend upon a number of factors including
practicality, space availability, cost, or personal preference.
Infection prevention considerations may influence the choice
of hand-drying method, but the evidence base is weak to make
informed decisions. Notably, the recent National Health Service (NHS) building guidance states that ‘Hot-air hand dryers
reduce paper waste and may be considered for use in public
areas of healthcare facilities, but should not be installed in
clinical areas as they are noisy and could disturb patients’.5 It is
clearly desirable to ensure that the process of hand drying does
not increase the potential for micro-organism transmission,
either directly to another person or indirectly by contamination of the bathroom environment.
Evidence concerning whether hand-drying methods differ in
their propensity to aerosolize, and so transmit microorganisms, is contradictory.6e11 Some studies suggest that
drying hands with warmed air is associated with increased
aerosolization of micro-organisms.11 However, others have
suggested that there is little difference in aerosolization for the
different drying methods.6 One of the reasons for discrepant
results may be the use of relatively insensitive methods or
experimental designs that fail to detect real differences. In this
study, we aimed to compare the propensity of three widely
used methods of hand drying (jet air dryer, warm air dryer, and
paper towel drying) to contaminate the environment with
bacteria via aerosolization during the drying process. Additionally, we investigated the extent of possible contamination
of people drying their hands, as well as the possibility of
contamination of a bystander.
Two electric hand dryers, a jet air dryer (Dyson Airblade)
and warm air dryer (Pro-Elec GSQ250B), and a paper towel
dispenser (Tork H3 classic dispenser containing Tork Advanced
Towels, MRT213) were mounted on one wall at manufacturerrecommended heights for use. Air was collected using two
Airtrace Environmental portable samplers (Biotrace, Microbial
Contamination Control, Runcorn, UK) via a 1 m long Tygon tube
placed at the left- and right-hand sides (LHS, RHS) of each
drying unit, in close proximity and also at 1 m away. As air
entered the sampler (28.3 L/min), it was forced through a fine
slit (44 0.152 mm) at a velocity of 70 m/s thereby causing
particulate matter (minimum size 0.4 mm) to impact upon a
140 mm diameter, lactobacillus-selective, agar plate (LAMVAB
agar, Bioconnections, Wetherby, UK, supplemented with vancomycin). The plate rotated constantly from a known start
point throughout the sampling period; thus, following culture,
the location of the colonies represents the time of recovery
from air. Following each test, the two plates (from the LHS and
RHS) were immediately transported to the laboratory and
incubated in an anaerobic cabinet at 37 C for 48e72 h, and
colonies were then counted. Data from each drying method
were compared using ManneWitney U-test (SPSS, IBM, Armonk,
NY, USA) using a 5% confidence level to determine significance.
In addition, four settle plates containing LAMVAB agar were
sited at various locations around each dryer (Figure 1). At the
end of each sampling session, the air-sampling machine was
cleaned externally and internally using a disinfectant (Trigene,
Medichem, Queenborough, UK) and run on a purge cycle to
decontaminate the machine and tubing, as recommended by
the manufacturer. Floor surfaces, the wall area around the
dryers, and the dryer units were also thoroughly cleaned between tests using Trigene.
Methods
Testing procedure
Organization of air sampling
Air-sampling tubes were clamped at a height of 1.2 m (from
floor level) on the LHS and RHS of the area where the drying of
lactobacilli-contaminated gloved hands was taking place, in
the outer edges of the airstream produced by the jet and warm
air dryers. To ensure reproducibility, this was the same relative
position for each of the hand-drying methods. For the tests 1 m
away from the hand drying, the ends of the air-sampling tubes
were clamped at the same height as before. The air samplers
were switched on and hands were then immediately dried. For
the warm air dryer, hands were rubbed together for 30e40 s
until dry; for the jet air dryer, hands were placed into the unit
and slowly drawn up until dry (15 s); for towel drying, four
paper towels were taken from the dispenser and these were
rubbed over hands until dry (15 s). The air samplers were left
running for 15 min following each hand-drying process.
All tests were carried out in a room measuring 65 m3 with the
door closed throughout experiments. Room air was maintained
by standard ventilation without air-conditioning or negative or
positive pressure ventilation. For each test, gloved hands were
first coated by immersion in a suspension of lactobacilli
(107 cfu/mL) that were cultured from a proprietary yoghurt
(Actimel, Danone, Paris, France) and then dried in a standardized manner using one of each of the three drying
methods: a warm air dryer, a jet air dryer, or paper towels. In
total, this part of the study comprised 120 air-sampling tests
(60 tests and 60 controls) with a total testing time of 15 min per
test (comprising up to 40 s of drying time dependent on the
method used and the remainder being the air-sampling time).
The 60 air-sampling tests of contaminated hands comprised 20
collections for each drying method, of which 10 were in close
proximity to the hands being dried and 10 were 1 m away.
Control air sampling was carried out before every hand-drying
test (with no hand drying taking place) both to provide baseline
measurements and to minimize the risk of carryover of
Air-sampling process
Visual determination of the extent of contamination
of the environment, user, and bystander
To visualize the extent of potential contamination occurring
during each drying process within the environment, and on to a
Please cite this article in press as: Best EL, et al., Microbiological comparison of hand-drying methods: the potential for contamination of the
environment, user, and bystander, Journal of Hospital Infection (2014), http://dx.doi.org/10.1016/j.jhin.2014.08.002
E.L. Best et al. / Journal of Hospital Infection xxx (2014) 1e8
Left-hand side
Hand
drier/paper
towel dispenser
mounted on
wall
3
Right-hand side
Immediate
vicinity (10 cm
from each side
of hand drier)
1 m away from
hand-drying area
2 m away from
hand-drying area
Figure 1. Locations of air-sampling tubes and settle plates. Diagram showing position of hand dryer and positions of the ends of the airsampling tubes for each of the three tests (black circles indicate the position of the end of the air sampler tubes) (mounted at a height of
1.2 m), white circles indicate position of settle plates on the floor.
user and a bystander, experiments were repeated as above.
However, for each test, gloved hands were coated in a solution
of black water-based paint (instead of lactobacilli), with the
user wearing a white disposable Tyvek suit (DuPont, Stevenage, UK); suits were worn backwards so that the hood covered
the face. Additionally, a bystander (wearing a suit in the same
manner) stood diagonally adjacent to the dryer user (1 m distance) in order to replicate the scenario of someone waiting to
dry his/her hands. In total, this user and bystander study
comprised 30 drying tests (10 tests for each drying method).
Following drying, the potential contamination within the
environment was visualized and enumerated by the distribution of black paint splatters around each drying unit, and the
distance travelled by the paint spots away from the drying
unit/area was measured. The extent of potential contamination on the user and bystander was quantified by counting the
numbers of paint spots on a number of predetermined areas
marked out on the Tyvek suits (Figure 2).
Results
Airborne lactobacilli counts during hand drying
For each drying method, the airborne bacterial counts were
very similar for samples collected on the LHS versus RHS of the
subject/dryer. Table I shows the combined LHS and RHS mean
counts (n ¼ 20) for each drying method. The air bacterial
counts in tests performed in close proximity to hand drying
Figure 2. White disposable Tyvek suit showing predetermined
areas used for counting paint spots.
Please cite this article in press as: Best EL, et al., Microbiological comparison of hand-drying methods: the potential for contamination of the
environment, user, and bystander, Journal of Hospital Infection (2014), http://dx.doi.org/10.1016/j.jhin.2014.08.002
4
E.L. Best et al. / Journal of Hospital Infection xxx (2014) 1e8
Table I
Mean lactobacilli counts (cfu) in the air after 15 min sampling for each drying method (n ¼ 10)
Distance
Close proximity
1 m away
Paper towels
Warm air dryer
Jet air dryer
LHS
(n ¼ 10)
RHS
(n ¼ 10)
Combined
(n ¼ 20)
LHS
(n ¼ 10)
RHS
(n ¼ 10)
Combined
(n ¼ 20)
LHS
(n ¼ 10)
RHS
(n ¼ 10)
Combined
(n ¼ 20)
2.6 (2.2)
2.4 (2.7)
2.6 (1.7)
2 (2.1)
2.6 (1.9)
2.2 (2.4)
14.9 (14.5)
18.2 (4.7)
16.5 (16)
19.1 (7.9)
15.7 (14.9)
18.6 (6.4)
76.2 (40)
89.1 (34.2)
65.2 (37.5)
89.9 (37.6)
70.7 (38.2)
89.5 (34.9)
LHS, left-hand side; RHS, right-hand side.
Values are mean (SD).
were 4.5-fold higher for the jet air dryer (70.7 cfu) compared
with the warm air dryer (15.7 cfu) (P ¼ 0.001) and 27-fold
higher compared with use of paper towels (2.6 cfu)
(P < 0.001). Airborne counts were also significantly different
during use of towel drying versus warm air dryer (P ¼ 0.001). A
similar pattern was seen in mean bacterial counts recovered
from air collected 1 m away from hand drying; bacterial air
counts recovered following use of the jet air dryer, warm air
dryer, and paper towels for hand drying were 89.5, 18.7, and
2.2 cfu, respectively. No lactobacilli were recovered in any
control air-sampling experiments.
The method enabled measurement of when bacteria were
recovered from air during the 15 min sampling periods. Using
the above test results, for the jet air dryer the mean proportions of bacteria recovered in the first, second, and third
5 min sectors (LHS and RHS, at all time-points, close to the
dryer) were 52%, 28%, and 20%. The corresponding data for the
warm air dryer were 50%, 24%, and 26%, and for the paper
towels were 46%, 39% and 15%. Similar trends were seen for the
bacteria recovered 1 m away from hand drying.
Settle plate lactobacilli counts
Settle plates located under each drying unit yielded the
greatest mean bacterial counts (Table II). Mean bacterial
counts for the 1 m distant settle plates (LHS and RHS results)
were combined, and results for the 10 tests at close proximity
and 1 m away were combined (n ¼ 20) as the positions of settle
plates remained the same. For the settle plates in close proximity to each drying method, counts under the dryer were the
highest for the warm air dryer (190 cfu) compared with the jet
air dryer (68.3 cfu) (P < 0.001) and the paper towel drying
(11.9 cfu) (P < 0.001). Counts on settle plates 1 m away for the
warm air dryer (7.8 cfu) were also higher than those for the jet
air dryer (2 cfu) (P < 0.001) and the paper towels (0.7 cfu)
(P < 0.001). There was no significant difference for the counts
for the one settle plate located 2 m away for the warm air dryer
and jet air dryer (both 1.4 cfu) (P ¼ 0.940). There was a significant difference between the counts on settle plates for the
paper towels (0.4 cfu) when compared to the warm air dryer
(P ¼ 0.040) and jet air drier (P ¼ 0.008). All settle plates for the
control experiments were negative.
Visualization tests to determine the extent of
contamination of the environment
Figures 3e5 show the distribution of paint following separate
drying episodes with hands coated in paint. For the jet dryer,
paint spots were found up to 120 cm away from the RHS of the
unit, 140 cm away on the LHS, 30 cm above the unit, and 85 cm
along the floor forwards towards the user (Figure 6). For the
warm air dryer, the maximum distance travelled by paint spots
was 30e40 cm on each side, 130 cm downwards along the wall
and 40 cm forwards along the floor towards the user (Figure 7).
For the hand towel drying process, markedly fewer paint spots
were visualized; a few were seen on the towel dispenser and on
the wall below, and some on the floor presumably due to
dripping while rubbing hands (Figure 8).
Table III shows mean numbers of paint spots detected during
hand drying (n ¼ 10) on each of the demarcated areas of the
body. No paint spots were seen on suits worn by the user or
bystander during hand drying using towels. Numbers of spots on
the user of the jet air dryer compared with the warm air dryer
were overall higher for all body areas, except for both arm
counts (mean counts: LHS arm 27.4 vs 14.8, P ¼ 0.061; RHS arm
8.7 vs 3.4, P ¼ 0.02). For both the jet air and warm air dryers,
spots predominated in the upper body area, with the numbers
Table II
Mean bacterial counts (mean cfu) on settle plates
Drying process
Paper towels
Warm air dryer
Jet air dryer
Position of settle plates
Under dryer
(n ¼ 20)
1 m awaya
(n ¼ 40)
2 m away
(n ¼ 20)
11.9
190
68.3
0.7
7.8
2
0.4
1.4
1.4
Results for 10 tests at close proximity and 1 m away were combined
as positions of settle plates remained the same.
a
Left- and right-hand-sided counts combined.
Figure 3. Visualization of paint spots following drying with the jet
air dryer.
Please cite this article in press as: Best EL, et al., Microbiological comparison of hand-drying methods: the potential for contamination of the
environment, user, and bystander, Journal of Hospital Infection (2014), http://dx.doi.org/10.1016/j.jhin.2014.08.002
E.L. Best et al. / Journal of Hospital Infection xxx (2014) 1e8
70 cm
140 cm
5
30 cm
76 cm
Jet air
drier
120 cm
Wall
Floor
100 cm
90 cm
85 cm
Figure 6. Furthest distance travelled by paint spots following one
drying process with the jet air dryer. Black arrows indicate distance along the wall on which the unit was mounted; red arrows
indicate distance forward along the floor.
Figure 4. Visualization of paint spots following drying with the
warm air dryer.
of spots from the jet air dryer being significantly higher [mean
counts of 144.1 and 65.8 (P ¼ 0.0005)]. Spot counts on upper
legs were higher after use of the jet air compared with the
warm air dryer [RHS mean counts 15 versus 1.6 (P ¼ 0.307) and
LHS 15.8 versus 3.4 (P ¼ 0.006)]. Similar spot counts were seen
on the lower legs (RHS mean counts 6.6 versus 4.3 (P ¼ 0.242)
and LHS 6.3 versus 2.8 (P ¼ 0.794). Relatively few spots were
detectable on the head area, with no significant difference
between the mean counts for the jet air dryer and the warm air
dryer [1.2 versus 0.5 (P ¼ 0.149)]. Overall, the mean number of
spots was significantly higher for the jet air dryer (mean counts
230.8) compared with the warm air dryer (135.1) (P ¼ 0.004).
The number of paint spots detectable on the bystander was
generally low for the air dryers (0.1e0.8). The body areas of
the bystander where we recorded paint spots after using the
jet air dryer were both arms (mean counts 0.1 for both), top of
the right leg (mean count 0.8), and both lower legs (mean
counts 0.3 for both). After using the warm air dryer, spots were
most frequently seen on the head (mean counts 0.2), upper
body (mean count 0.2), both upper legs (mean counts 0.2 and
0.4), and right lower leg (mean count 0.5). Overall, there was
no significant difference when comparing the mean number of
spots on the bystander with the jet air and warm air drying
approach [mean counts 1.6 versus 1.5 (P ¼ 0.548)].
Discussion
Hand drying is an integral part of the hand hygiene process,
which aims to optimize the removal of potentially pathogenic
30 cm
Warm air
drier
130 cm
40 cm
Wall
Floor
40 cm
Figure 5. Visualization of paint spots following drying with the
hand towels.
Figure 7. Furthest distance travelled by paint spots following one
drying process with the warm air dryer. Black arrows indicate
distance along the wall on which the unit was mounted; red arrow
indicates distance forward along the floor.
Please cite this article in press as: Best EL, et al., Microbiological comparison of hand-drying methods: the potential for contamination of the
environment, user, and bystander, Journal of Hospital Infection (2014), http://dx.doi.org/10.1016/j.jhin.2014.08.002
6
E.L. Best et al. / Journal of Hospital Infection xxx (2014) 1e8
Paper towel
dispenser
20 cm
Wall
20 cm
Floor
Figure 8. Furthest distance travelled by paint spots following one
drying process with the paper towels. Black arrows indicate distance along the wall on which the unit was mounted; red arrow
indicates distance forward along the floor.
micro-organisms that may be acquired during toileting and use
of bathrooms. The published evidence concerning whether
hand-drying methods may differ in their propensity to aerosolize and so transmit micro-organisms is contradictory.6e11
Some studies suggest that drying hands via warmed air is
associated with increased aerosolization of micro-organisms,
and others suggest there to be no difference.12 Methodological issues may explain these discrepancies.
This study has demonstrated marked differences in the
extent of aerosolization of bacteria during three different
hand-drying methods, using a detection method that has been
used in the clinical setting to examine the transmissibility of
Clostridium difficile.13 In the present experiments, we used a
presumed non-pathogenic bacterium that was isolated from a
proprietary probiotic yoghurt. We have also shown clear differences between the methods in the degree of visible
splashing during hand drying, using paint spots, resulting in
contamination of both the user and bathroom environment.
Taylor et al. found no difference in the numbers of microorganisms remaining on hands following washing and drying
with paper towels or with a warm low-velocity air dryer.6 They
also sampled the air in the immediate vicinity of hands being
dried in an enclosed cabinet, and reported that both methods
contribute equally to aerosolization of bacteria. Matthews and
Newsom compared dryers and towels using whole-hand impressions on agar plates and found no difference in the
numbers of bacteria remaining on hands.8 No differences were
observed in airborne bacterial counts sampled during drying
with warm air dryers compared with hand towels. Meers and
Leong collected air using a Casella slit air sampler before,
during and after drying hands using a warm air hand dryer, and
more bacteria were detected in the air during and after
compared with before drying.11 Dispersal of marker bacteria
during use of a warm air dryer was up to three feet away and
included the investigator’s laboratory coat; no such spread was
seen during paper towel drying.11 Gendron et al. reported no
evidence of airborne transmission during paper towel
dispensing.14 There are few studies comparing airborne
contamination associated with jet air dryers versus other
methods of drying. Snelling et al. compared warm air dryers to
a jet air dryer and found that the latter was superior for
reducing bacterial transfer from hands.15 Given the use of a
standard method of contaminating hands prior to drying, these
data can be interpreted to show that greater removal (aerosolization) of bacteria occurred during use of the jet air dryer.
In a recent study of 100 volunteers using either paper towels or
a jet air dryer, more droplets and greater dispersal was seen
during jet air drying.16
Scoping experiments were carried out to determine the best
way of reproducibly measuring the extent of airborne dispersal
of micro-organisms during hand drying (data not shown). We
found that airborne bacterial counts of skin-type micro-organisms during hand drying were difficult to distinguish from
those measured when no hand drying occurs. This reflects the
background counts of such bacteria (present on skin scales)
that are liberated during normal human activity. We concluded
that using an indicator bacterial strain (chosen as it can be
identified amongst background contaminants that are found
normally in air and because it is considered to be harmless) to
seed gloved hands provided the most reproducible method to
measure dispersed bacteria during hand drying. This approach
allowed the same subject to carry out multiple repeats without
the risk of skin damage (due to repeated washing/drying),
which would risk confounding the results obtained, i.e. produce results that are erroneous and which potentially fail to
Table III
Mean paint spot counts (n ¼ 10) on different body areas for each different drying method for the user of the dryer and bystandera
Area of body (size of area used for counting spots)
Head (14 9 cm)
Arm (LHS) (24 13 cm)
Arm (RHS) (24 13 cm)
Upper body (36 26 cm)
Lower body (24 13 cm)
Right leg e upper (24 13 cm)
Right leg e lower (24 13 cm)
Left leg e upper (24 13 cm)
Left leg e lower (24 13 cm)
Jet air dryer
Warm air dryer
Paper towels
User
Bystander
User
Bystander
User
Bystander
1.2
14.8
3.4
144.1
23.6
15
6.6
15.8
6.3
0
0.1
0.1
0
0
0.8
0.3
0
0.3
0.5
27.4
8.7
65.8
20.6
1.6
4.3
3.4
2.8
0.2
0
0
0.2
0
0.2
0.5
0.4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
LHS, left-hand side; RHS, right-hand side.
a
See Figure 2 for body areas.
Please cite this article in press as: Best EL, et al., Microbiological comparison of hand-drying methods: the potential for contamination of the
environment, user, and bystander, Journal of Hospital Infection (2014), http://dx.doi.org/10.1016/j.jhin.2014.08.002
E.L. Best et al. / Journal of Hospital Infection xxx (2014) 1e8
detect real differences in microbe dispersal during hand drying. The capacity to carry out multiple repeats adds considerable rigour to the results. The use of an indicator bacterial
strain, seeded in numbers that reflect microbe counts found on
poorly washed hands (and also recommended for this type of
evaluation in British Standard EN1500 test procedure), was
used to measure the dispersal of microbes that are not normal
skin inhabitants, but which may contaminate hands during
toileting.3,17,18
In the present study, counts of airborne lactobacilli were
four- and 26-fold higher in the immediate vicinity of the jet air
dryer than those associated with the warm air dryer and paper
towels, respectively. Bacteria persisted in the air well beyond
the 15 s hand-drying time, with approximately half of the
lactobacilli collected more than 5 min after drying ceased.
Aerosolized bacteria were dispersed 1 m away from the jet air
dryer within the first 5 min of air sampling. As air is emitted
from the jet air dryer at speeds of up to 400 mph, it is not
surprising that bacteria were recoverable in similar quantities
in the immediate vicinity of, and 1 m away from, the machine.
Bacterial counts on settle plates at 1 and 2 m away, as well as
visual inspection of paint dispersed in the environment and on
to the user, demonstrate widespread droplet release during
drying with a jet air dryer. Droplets contaminated all areas of
the body, including the head, albeit in smaller numbers. There
is, therefore, the potential for splattering on to persons other
than the person drying their hands, and possibly inhalation of
microbes sheared off hands during drying. The extent of
contamination during use of the warm air dryer was not as
widespread as with the jet air dryer, likely reflecting the
lower speed of the air being emitted and its downwards, as
opposed to upwards, trajectory. However, the prolonged
drying time required for drying hands with a warm air dryer
may add to the dissemination of airborne bacteria. Bacteria
recovered from the air were four-fold less than with the jet
air dryer, but counts in air collected at close proximity and
1 m away were similar, suggesting that distribution of airborne
bacteria can also be widespread with this drying method. The
mean bacterial counts on the settle plates were highest after
use of the warm air dryer, which probably reflects the
downwards trajectory of air and droplets, as demonstrated by
paint splatter patterns (Figure 4). We confirmed this finding by
the distribution of paint spots on the suit of the user; whereas
there were generally fewer spots than seen on the suits worn
by the user of the jet air dryer, these were detectable all over
the body. These findings were similar to those of Ngeow
et al.19
Our data show that hand drying with paper towels contributed the least with respect to airborne contamination up to 1 m
away, as reported elsewhere.14 Although a few bacteria were
detectable in the air following paper towel drying, the low
numbers were similar close and 1 m away from the point of hand
drying. Likewise, very few bacteria were recovered on the
settle plates. We detected negligible dispersal of paint droplets
(up to 20 cm) during paper towel hand drying (Figures 6 and 8),
and those detected mostly seem to relate to towel removal from
the dispenser. We used four paper towels to dry hands in each
test, and so the repetitive towel removal likely contributed
towards the paint spots visualized on the dispenser and
adjoining wall. However, paper towel use was not associated
with paint dispersal to the body of the user or bystander. Our
results suggest that paper towel use contributes less than either
7
of the air dryer machines to microbial contamination of the
bathroom environment and individuals within.
Some studies have reported an increase in the numbers of
bacteria during drying with paper towels compared with drying
with a warm air dryer.12,20,21 Soap can disrupt skin commensals,
and vigorous hand rubbing while drying disrupts skin squames
and brings bacteria from within pores to the surface, thereby
increasing numbers of shed bacteria. Meers and Yeo confirmed
this by air sampling, and reported that bacteria and skin
squames were increased after washing and drying using paper
towels.21 Yamamoto et al. evaluated the efficiency of warm air
and paper towel drying for the removal of bacteria from
washed hands.22 They concluded that holding hands stationary
and not rubbing was desirable for removing bacteria and that
paper towels were useful for removing bacteria from the fingertips but not from the hands and fingers. Snelling et al. also
reported that rubbing hands during drying with a warm air
dryer can increase the numbers of bacteria on the skin.15
There are some weaknesses and limitations to the present
study. Experiments involved gloved hands, and therefore we
potentially underestimated the effect of released skin squames
and ensuing bacterial dissemination. We used relatively high
inocula to simulate poorly washed hands; clearly lower levels
of microbe aerosolization would be expected for only minimally contaminated hands. Unfortunately, however, there is a
perception that inadequate handwashing and drying after toileting occurs rather frequently.23e26 Drying was carried out for
a set length of time for each method, whereas in previous
studies this has continued until hands felt dry (not practicable
with gloved hands). Shorter ‘drying’ times could be expected to
result in less microbe aerosolization, although at a possible
cost of damp hands, itself a potential transmission risk. The
subject carrying out the hand drying was of average height;
results may have been altered for a smaller adult or children,
as potential contamination could be greater on the upper body
or head. We only examined two types of air dryers and many
others are available; this may limit extrapolation of our results.
We note that some dryers claim to filter air, but this applies
only to incoming air and not to that which is ejected from the
machine and can become contaminated with microbes from
hands.
Whereas this study has demonstrated that the use of paper
towels may be superior in terms of microbe aerosolization risk,
some have reported the possibility of transmission associated
with paper towels or dispensers. Harrison et al. reported that
transfer of bacteria between paper-towel dispensers and hands
can take place if either one is contaminated, although this is
dependent on the design, construction, and positioning of
these devices.27,28 Gendron et al. detected a large community
of culturable bacteria including toxin producers, on unused
paper towels, which may be transferred to users.14 Others have
demonstrated, via air sampling, that sacks of used paper
towels were a possible source of contamination in operating
theatres.29
Paper towels have drawbacks, which include the need to
manage the accumulation of waste in bathrooms. Dispensers
and air dryers need to be cleaned and/or designed in such a
way that surface contamination and ensuing risk of transfer of
microbes to hands is minimized. Short drying times associated
with jet air dryers may encourage greater compliance with
hand drying. However, our results demonstrate that jet air and
warm air dryers increase the numbers of airborne bacteria
Please cite this article in press as: Best EL, et al., Microbiological comparison of hand-drying methods: the potential for contamination of the
environment, user, and bystander, Journal of Hospital Infection (2014), http://dx.doi.org/10.1016/j.jhin.2014.08.002
8
E.L. Best et al. / Journal of Hospital Infection xxx (2014) 1e8
within the bathroom environment. Increased dispersal of microbes during hand drying could be an important consideration
in the healthcare setting for bacteria, such as Staphylococcus
aureus and Escherichia coli, and for viruses including norovirus
and influenza viruses.30 There is a concern that droplets/particles released during hand drying could transmit respiratory
viruses such as influenza from contaminated hands or air. Both
possibilities would appear to be more likely with jet air dryers,
particularly if these shower droplets towards the face of the
user, although the magnitude of risk remains unclear.
Jet air and warm air dryers result in increased bacterial
aerosolization when drying hands. These results suggest that
air dryers may be unsuitable for use in healthcare settings, as
they may facilitate microbial cross-contamination via airborne
dissemination to the environment or bathroom visitors.
Conflict of interest statement
M.H.W. has received honoraria from ETS for microbiological
advice and travel expenses to attend an ETS meeting.
Funding sources
The project was funded by the European Tissue Symposium
(ETS).
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Please cite this article in press as: Best EL, et al., Microbiological comparison of hand-drying methods: the potential for contamination of the
environment, user, and bystander, Journal of Hospital Infection (2014), http://dx.doi.org/10.1016/j.jhin.2014.08.002