Evaluation of the potential for virus dispersal during hand drying: A comparison of three methods

Abstract

Aims:
To use a MS2 bacteriophage model to compare three hand-drying methods, paper towels (PT), a warm air dryer (WAD) and a jet air dryer (JAD), for their potential to disperse viruses and contaminate the immediate environment during use.

Methods and results:
Participants washed their gloved hands with a suspension of MS2 bacteriophage and hands were dried with one of the three hand-drying devices. The quantity of MS2 present in the areas around each device was determined using a plaque assay. Samples were collected from plates containing the indicator strain, placed at varying heights and distances and also from the air. Over a height range of 0.15-1.65 m, the JAD dispersed an average of >60 and >1300-fold more plaque-forming units (pfu) compared to the WAD and PT (P <0.0001), respectively. The JAD dispersed an average of >20 and >190-fold more pfu in total compared to WAD and PT at all distances tested up to 3 m (P <0.01), respectively. Air samples collected around each device 15 minutes after use indicated that the JAD dispersed an average of >50 and >100-fold more pfu compared to the WAD and PT (P <0.001), respectively.

Conclusions:
Use of the JAD lead to significantly greater and further dispersal of MS2 bacteriophage from artificially contaminated hands when compared to the WAD and PT.

Significance and impact of study:
The choice of hand drying device should be considered carefully in areas where infection prevention concerns are paramount, such as healthcare settings and the food industry. This article is protected by copyright. All rights reserved.

Full text

ORIGINAL ARTICLE
Evaluation of the potential for virus dispersal during hand
drying: a comparison of three methods
P.T. Kimmitt and K.F. Redway
Department of Biomedical Sciences, Faculty of Science and Technology, University of Westminster, London, UK
Keywords
aerosolization, cross-contamination, dispersal,
hand drying, hand hygiene, MS2
bacteriophage, virus.
Correspondence
Patrick T. Kimmitt, Department of Biomedical
Sciences, Faculty of Science and Technology,
University of Westminster, 115 New Cavend-
ish Street, London W1W 6UW, UK.
E-mail: p.kimmitt@westminster.ac.uk
2016/1655: received 18 August 2015, revised
12 November 2015 and accepted 22 Novem-
ber 2015
doi:10.1111/jam.13014
Abstract
Aims: To use a MS2 bacteriophage model to compare three hand-drying
methods, paper towels (PT), a warm air dryer (WAD) and a jet air dryer
(JAD), for their potential to disperse viruses and contaminate the immediate
environment during use.
Methods and Results: Participants washed their gloved hands with a
suspension of MS2 bacteriophage and hands were dried with one of the three
hand-drying devices. The quantity of MS2 present in the areas around each
device was determined using a plaque assay. Samples were collected from
plates containing the indicator strain, placed at varying heights and distances
and also from the air. Over a height range of 015–165 m, the JAD dispersed
an average of >60 and >1300-fold more plaque-forming units (PFU) compared
to the WAD and PT (P<00001), respectively. The JAD dispersed an average
of >20 and >190-fold more PFU in total compared to WAD and PT at all
distances tested up to 3 m (P<001) respectively. Air samples collected
around each device 15 min after use indicated that the JAD dispersed an
average of >50 and >100-fold more PFU compared to the WAD and PT
(P<0001), respectively.
Conclusions: Use of the JAD lead to significantly greater and further dispersal
of MS2 bacteriophage from artificially contaminated hands when compared to
the WAD and PT.
Significance and Impact of Study: The choice of hand-drying device should be
considered carefully in areas where infection prevention concerns are
paramount, such as healthcare settings and the food industry.
Introduction
The importance of hand hygiene in minimizing the risk
of transmission of pathogenic micro-organisms has been
recognized since Semmelweis’s work on puerperal fever
transmission (Codell Carter 1983). Hand hygiene is con-
sidered to be an integral component of the practice of
infection control both in the home and in community
and healthcare settings (Curtis et al. 2003; Bloomfield
et al. 2007). It has been estimated that cross-infection
contributes to 40% of cases of healthcare-associated
infections and hand hygiene compliance represents an
essential step in minimizing such infections (Pittet 2000;
Weist et al. 2002; Pittet et al. 2006). Hand hygiene
comprises two different possible procedures; decontami-
nation using a hand sanitizer, such as alcohol, or washing
with soap and water and, with the latter, drying of the
hands by various methods.
In healthcare settings, the appropriate cleansing of the
hands of staff or visitors prior to, or after, certain proce-
dures is of particular importance and various guidelines
on hand washing and cleansing have been issued by the
CDC (Centers for Disease Control and Prevention 2002),
the NHS (National Health Service) and the WHO (World
Health Organization) (Boyce and Pittet 2002; WHO 2009;
NHS Professionals 2013). The WHO guidelines state that
water alone is unsuitable for cleaning visibly soiled hands
and that soap or detergent must be used as well as water.
Journal of Applied Microbiology 120, 478--486 ©2015 The Society for Applied Microbiology478
Journal of Applied Microbiology ISSN 1364-5072

There has been much research on the effectiveness of
soap and other agents in reducing the microbial count of
both resident and transient flora on the hands. A study
and review of the literature concluded that the main fac-
tors affecting bacterial counts on the hands were the
hand sanitizer or soap used and the drying method
(Montville et al. 2002) and that hands which are inade-
quately dried are more likely to transmit micro-organ-
isms when compared to those which have been
completely dried (Patrick et al. 1997).
The importance of thorough cleansing of the hands
with soap and water or a hand sanitizer to reduce health-
care-associated infections is well documented, having
been publicized for years such as by National Health Ser-
vice poster campaigns and by initiatives such as the
Cleanyourhands campaign (Stone et al. 2012). However,
in reality the general public and some healthcare profes-
sionals do not always follow the advice. Washing proce-
dures can be poor and compliance rates low (Knights
et al. Unpublished data; Anderson et al. 2008).
If it is accepted that the hands become contaminated
with micro-organisms when using the toilet, these studies
would indicate that, due to low compliance rates and
inadequate hand cleansing procedures, the majority of
persons drying their hands in washrooms are likely to
have microbial contamination on their hands when they
dry them. This has implications for the aerosolization
and dispersal of that contamination by the hand-drying
method that is used and the risk of transmission of
potentially disease-causing micro-organisms into the
washroom environment and to other persons using the
washroom.
There are a number of different methods available for
hand drying in public washrooms. These include paper
towels, continuous roller towels, warm air dryers and jet
air dryers. There have been relatively few studies evaluat-
ing the capacity for the different hand-drying devices to
aerosolize and disperse microbial contamination on the
hands into the immediate environment and to other per-
sons using a washroom. Matthews and Newsom (1987)
concluded that there was no significant difference
between warm air dryers and paper towels in terms of
aerosol liberation and that the former could be consid-
ered safe but Ngeow et al. (1989) demonstrated the dis-
persal of marker bacteria within a radius of 1 m from a
warm air dryer. When comparing the use of paper towels
with a jet air dryer to dry the hands of 100 volunteers,
Margas et al. (2013) showed that the two hand-drying
methods produced different patterns of ballistic droplets:
the jet air dryer producing a greater number of droplets
dispersed over a larger area and more microbial contami-
nation of the immediate environment than paper towels.
Best et al. (2014) used a paint and a Lactobacillus bacte-
rial model to compare aerosolization and dispersal fol-
lowing hand drying with paper towels, a warm air or jet
air dryer. They showed that paper towels produced less
dispersal from the hands into the surrounding environ-
ment than jet air dryers. Using an acid-indicator model
and artificial contamination of the hands with yeast, Best
and Redway (2015) demonstrated that the use of a jet air
dryer to dry the hands dispersed liquid, and, conse-
quently, potential microbial contamination on the hands,
to greater distances (up to 15 m) than paper towels,
roller towels or warm air dryers (up to 075 m). In the
same study, jet air dryers were also shown to disperse
more liquid from the hands to a range of different
heights compared to the other hand-drying methods.
However, such studies have focused on micro-organisms
other than viruses and to date there have been few stud-
ies to evaluate the aerosolization and dispersal of virus
particles during hand drying.
Viral pathogens such as Norovirus are thought to have
a low infectious dose and can be shed in large numbers
in faeces (Gerhardts et al. 2012). In a review, Kampf and
Kramer (2004) cited studies that show that viruses can
survive on the hands for varying times; Influenza and
CMV (10–15 min), HSV (up to 2 h), Adenovirus (for
many hours), Rhinovirus (7 days) and Rotavirus and
HAV (up to 60 days). Therefore, virus dispersal in the
washroom has the potential to contaminate persons and
surfaces, including those of hand-drying devices.
This study used bacteriophage MS2 as a surrogate for
nonenveloped human viruses. MS2 has been used in this
way in a number of prior studies due to its stability and
similar characteristics to human enteric viruses such as
Picornaviruses and Caliciviruses, including Norovirus
(Sickbert-Bennett et al. 2005; Gerhardts et al. 2012).
Additionally, MS2 has the added advantage in that virus
numbers can be readily quantified using a plaque assay.
In this work, the capacity for three hand-drying devices,
namely paper towels, a warm air dryer and a jet air dryer,
to aerosolize and disperse water on the hands, and con-
taminate the air and surfaces around the drying device
with MS2 phage was investigated.
Materials and methods
Preparation and use of MS2 bacteriophage
MS2 bacteriophage (ATCC 15597-B1) was propagated at
37°C overnight in log phase tryptone soya broth (Oxoid,
Basingstoke, UK) cultures of Escherichia coli (ATCC
15597) to yield a mean count in the range of 10
10
pla-
que-forming units (PFU) per mL. Following infection,
nonlysed bacteria were removed by centrifugation
(3000 g, 10 min) and the supernatant phage suspension
Journal of Applied Microbiology 120, 478--486 ©2015 The Society for Applied Microbiology 479
P.T. Kimmitt and K.F. Redway Virus dispersal during hand drying

generated was used in subsequent experiments. Each
batch of phage suspension was titrated on the same day
as experiments were performed to ensure that approxi-
mately equal numbers of phage particles were used each
time. Participants were asked to rinse their gloved hands
in 50 ml of the phage suspension for 10 s and simulate
the process of washing during this period followed by
shaking three times and then drying them using one of
the hand-drying devices. All experimental work took
place in a university teaching laboratory and the washing
and drying areas were separated by a distance of approx.
5m.
For quantitative detection of MS2 phage, plates of
tryptone soya agar (TSA) (Oxoid) were overlaid with a
thin layer of 05% sloppy TSA containing 1% (v/v) log
phase Escherichia coli (ATCC 15597). Dispersal experi-
ments were performed and, following incubation over-
night at 37°C, the number of plaque-forming units
determined by visualization and counting of plaques.
Hand-drying devices
Three hand-drying methods were compared in this study;
the use of two paper towels (Wepa Clou Comfort, Arns-
berg, Germany) for 10 s, warm air drying (World Dryer
Corporation, Berkeley, IL), model LE48 for 20 s and jet
air drying (Dyson, Malemsbury, UK), model AB01 for
10 s. Drying times for the paper towel and warm air
dryer were based on the mean times recorded during the
observation of 292 members of the public in male and
female washrooms in various London locations (Knights
et al. Unpublished data). The 10-s drying time for the jet
air dryer was based on the manufacturer’s recommenda-
tions displayed on the device. The devices were mounted
onto a wooden board placed at a height that would be
typical for use in a washroom. The dryers used were not
new but had never been used in a washroom and were
decontaminated between tests by thorough wiping with
70% (v/v) ethanol.
Virus dispersal at different heights and distances
90 mm diameter Petri dishes (Fisher Scientific, Lough-
borough, UK) containing TSA and an overlay of the
E. coli host were affixed to a vertical board at intervals of
030 m at six different heights (015, 045, 075, 105,
135 and 165 m) from the floor. The agar plates were
affixed to the mid-point of six zones (1–6) chosen to
represent a typical human torso, including head, trunk
and legs, of a person using a washroom (Fig. 1). During
tests, the vertical board was held 04 m from the hand-
drying device; this distance being based on measurement
of the mean distance between multiple hand-drying
devices in large public washrooms at a mainline railway
station.
Air sampling
An Air Trace
â
Environmental air sampler (Biotrace, Run-
corn, UK) model ATEM 240 with a 1 m Tygon tube was
used to sample air in the vicinity of each hand-drying
device at a rate of 283 l min
1
, a total of 4245 l of air
was sampled. The air was impacted at 70 m s
1
via a
44 90152 mm slit onto a rotating 140 mm Petri dish
(Fisher Scientific) containing 05% sloppy TSA with 1%
(v/v) log phase Escherichia coli (ATCC 15597).
Petri dishes were orientated so that the start point
could be determined and sampling was performed over a
period of 15 min, after which the plate had made one
complete rotation. The air sampler was subjected to a 1-h
purge cycle before and after daily use and in between
changes of hand-drying device. In addition, a 15-min
control air sample was collected before each run or
change of hand-drying device. As with the height and
distance dispersal experiments, settle plates were placed
around each device to confirm that no residual MS2
phage was present at the beginning and end of each test
run.
In order to assess virus dispersal in air a method based
on that used by Best et al. (2014) was employed. The
Tygon tube inlet was placed at a height of 12 m which
corresponded to the height of both the bottom of the
paper towel dispenser and the bottom of the warm air
dryer and was 025 m above the height of the jet air
dryer.
(1·65 m)
(1·35 m)
(1·05 m)
(0·75 m)
(0·45 m)
(0·15 m)
ZONE 1
ZONE 2
ZONE 3
ZONE 4
ZONE 5
ZONE 6
Figure 1 Photograph of vertical board with human figures and dia-
gram showing the 6 different height zones and height of mid-point
from floor (m) used to assess vertical dispersal.
Journal of Applied Microbiology 120, 478--486 ©2015 The Society for Applied Microbiology480
Virus dispersal during hand drying P.T. Kimmitt and K.F. Redway

Air samples were collected at three different positions
(Fig. 2):
i At a distance of 01 m from the left and right-hand
side of each device;
ii At a distance of 1 m from the left and right-hand side
of each device;
iii At a 1 m distance behind and offset by 03 m from
the right-hand side of the device.
Two participants were used and an equal number (10)
of samples were taken from the left and right-hand side
for each of the distances and positions used. The
sequence by which different samples were collected and
devices tested was randomised.
After incubation, plates were divided into six sectors,
each sector representing a 25-min time interval and the
number of PFU in each sector was counted. Where pla-
que formation was confluent, semi-confluent or uncount-
able, and for calculation purposes, the number of plaques
per sector was recorded as follows: confluent plaque for-
mation was scored as 500 per sector; confluent/semi-con-
fluent plaque formation was scored as 400 per sector;
semi-confluent plaque formation was scored as 300 per
sector; uncountable numbers of plaque were scored as
200 per sector. Uncountable refers to the presence of dis-
crete plaques that were present in high numbers which
could not be counted with accuracy.
When necessary to enable visualization of plaques as
clear areas against a red background, the plates were
flooded with tryptone soya broth (Oxoid) containing
01% (w/v) 2,3,5, triphenyltetrazolium chloride (Fisher
Scientific) followed by incubation at 37°C for 20 min
(Pattee 1966).
Statistical analysis
Data from plaque assays were analysed by Students t-test
using MICROSOFT EXCEL (Microsoft, Redmond, WA), with a
confidence interval of 95%. A Pvalue of <005 was used
to denote statistical significance.
Results
Virus dispersal at different heights
The vertical board with attached Petri dishes was divided
into six zones to compare virus dispersal at a range of
heights covering a range of 015–165 m (Fig. 1). For
each of the six zones, a total of at least ten replicates were
used for each hand-drying device performed approxi-
mately equally on the left and right-hand side of the
device.
The jet air dryer dispersed a significantly greater num-
ber of virus particles than the other hand-drying devices
(Table 1). The greatest mean number of PFU was
observed in zones 3 (075 m) and 4 (105 m), 710 and
834 PFU respectively. These two zones represented nearly
70% of the total detected virus dispersed by the jet air
dryer. In contrast, the warm air dryer dispersed a mean
of 5 PFU in zone 4, 167-fold lower than the jet air dryer
and with the difference being significant (P<00001).
Paper towels dispersed a mean of 01 PFU in zone 4,
8340-fold lower than the jet air dryer (P<00001). Con-
trol samples collected with the devices switched off and
0·3 m<<>>0·7 m
1
3
2
DEVICE
Figure 2 Diagram showing the three different air sampling positions
used in this study.
Table 1 Counts of viral plaques on 90 mm agar plates of a bacterial
lawn at different heights at a set distance (04 m) from hand-drying
devices used to dry the hands of participants after contamination
with a bacteriophage suspension. Data are presented as means with
standard deviation in parentheses
Height zone
Height
from
floor (m)
Mean number of plaques (SD)
Paper
towel
Warm air
dryer Jet air dryer
1165 05(10) 07(17) 2489 (3096)
2135 07(16) 87 (107) 3359 (2850)
3105 01(03) 46(49) 7095 (3319)
4075 01(03) 54(65) 8336 (2583)
5045 01(03) 39(45) 639 (897)
6015 01(03) 111 (146) 269 (444)
N111111
Mean
total number
(all heights)
16344 22187
Journal of Applied Microbiology 120, 478--486 ©2015 The Society for Applied Microbiology 481
P.T. Kimmitt and K.F. Redway Virus dispersal during hand drying

performed before and after each experiment yielded no
plaques.
Virus dispersal at different distances
Comparisons of virus dispersal at varying distances from
the hand-drying device were performed using Petri dishes
placed on a vertical surface at 025–05 m intervals and
ten replicates were assayed for each distance point, per-
formed equally on the left and right-hand side of the
device. Distances from 0 to 3 m were compared and at
all distances tested the jet air dryer dispersed significantly
greater (P<001) numbers of virus particles than either
the warm air dryer or paper towel devices (Table 2). For
the jet air dryer, the maximum mean number of PFU
was seen 025 m from the device and there was a decline
in PFU with increasing distance from the device. How-
ever, the mean number of PFU observed 3 m from the
device was more than 500-fold greater than that for the
warm air dryer and paper towel devices (Fig. 3). Control
samples collected with the device switched off and per-
formed before and after each experiment yielded no pla-
ques.
Air sampling
For all three devices, PFU counts were generally greater
when air samples were collected closer to the device, in
this case 01 m compared to 1 m (Table 3) and the num-
ber of detectable PFU decreased over time (Fig. 4). How-
ever, airborne virus counts for the jet air dryer were
significantly greater (P<0001) than those for the warm
air dryer and paper towel devices for each position and
for each time interval.
For the jet air dryer, during the immediate 25 min
after use and at 01 m from the device, 30-fold and 13-
fold more PFU were detected in air compared to the
warm air dryer and paper towel devices respectively (be-
tween which there was no significant difference). For the
last time period (125–15 min) after hand drying, more
than 50-fold numbers of PFU were detected when the jet
air dryer was tested at any of the three sample positions
used compared to paper towels and the warm air dryer.
The number of PFU detected in the air from the jet air
Table 2 Counts of viral plaques on 90 mm agar plates of a bacterial
lawn at a set height (071 m) and at different distances from hand-
drying devices used to dry the hands of participants after contamina-
tion with a bacteriophage suspension. Data are presented as means
with standard deviation in parentheses
Distance
from device (m)
Mean number of plaques (SD)
Paper towel Warm air dryer Jet air dryer
000 132(84) 502 (261) 5655 (4271)
025 00(00) 490 (313) 9240 (1946)
050 00(00) 38(23) 5468 (4285)
075 00(00) 11(14) 3221 (3194)
100 20(28) 02(04) 2123 (2245)
150 02(04) 02(04) 2143 (1908)
200 00(00) 00(00) 1845 (2150)
250 00(00) 00(00) 1799 (2051)
300 00(00) 03(06) 1774 (2435)
N101020
Mean
total number
(all distances)
154 1037 30045
1000·0
800·0
600·0
400·0
Mean number of plaques per plate
200·0
0·0
0·00 0·50 1·00 1·50
Distance (m)
2·00 2·50 3·00
Figure 3 Mean number of viral plaques per
90 mm bacterial overlay agar plate detected
at different distances after use of three hand-
drying devices: jet air dryer (●); warm air
dryer (■); paper towel (▲). Standard error
bars are shown.
Journal of Applied Microbiology 120, 478--486 ©2015 The Society for Applied Microbiology482
Virus dispersal during hand drying P.T. Kimmitt and K.F. Redway

dryer showed exponential decline with an acceptable
coefficient of determination (R²)of09781.
When drying hands using paper towels, virus counts in
the air to the sides of the device were slightly higher than
those obtained using a warm air dryer for most of the
time periods but this difference was not statistically sig-
nificant. Additionally, sampling at 1 m offset by 03m
behind the device produced no statistical difference
between paper towels and warm air drying. Control sam-
ples run before and after each experiment yielded no pla-
ques and no differences could be detected between
sampling on the left or right-hand side of any of the
hand-drying devices.
Discussion
When the three hand-drying devices were compared in
this study, there were clear differences in the extent of
virus dispersal from the hands. This was evident from the
results of the experiments in which MS2 was dispersed
from the hands and transferred onto agar plates affixed
at varying heights and distances from the hand-drying
devices and also into the air as sampled at three different
positions in the vicinity of the device. In each case, the
jet air dryer produced significantly greater virus dispersal
compared to the warm air dryer and paper towel devices.
Combined results for all six heights tested showed that
Table 3 Counts of viral plaques produced by air sampling at three different positions onto 140 mm agar plates of a bacterial lawn at different
times over a 15-min period after use of hand-drying devices to dry the hands of participants subsequent to contamination with a bacteriophage
suspension
Time (min) Distance (m) Position
Mean number of plaques (SD)
Paper towel Warm air dryer Jet air dryer
00–2501L&R367 (245) 159 (126) 4700 (458)
10L&R178 (215) 92 (100) 3500 (1025)
10/03B 69(88) 91(82) 3430 (790)
Mean total (L, R & B) 205 (231) 114 (109) 3877 (978)
Max/Min 790/00350/00 5000/2000
25–500152(38) 44(3
5) 2357 (500)
1068(65) 52(75) 2000(00)
10/0337(38) 73(86) 2300 (458)
Mean total (L, R & B) 52(51) 56(70) 2267 (428)
Max/Min 190/00270/00 3000/2000
50–750142(45) 22(26) 1798 (610)
1023(40) 19(25) 1345 (615)
10/0327(29) 55(52) 1220 (604)
Mean total (L, R & B) 31(39) 32(40) 1454 (661)
Max/Min 130/00160/00 3000/180
75–1000118(19) 27(22) 1012 (471)
1019(28) 10(09) 858 (661)
10/0324(30) 12(15) 703 (634)
Mean total (L, R & B) 20(26) 16(18) 858 (617)
Max/Min 90/0050/00 2000/40
100–1250111(27) 18(25) 572 (542)
1009(16) 08(15) 465 (360)
10/0304(09) 19(23) 439 (458)
Mean total (L, R & B) 08 (231) 15(22) 492 (471)
Max/Min 90/0080/00 2000/20
125–1500100(00) 14(21) 610 (482)
1010(20) 05(12) 385 (318)
10/0301(03) 06(12) 318 (380)
Mean total (L, R & B) 04(13) 08(16) 438 (425)
Max/Min 60/0060/00 1860/00
Data are presented as means with standard deviation in parentheses. L, left-hand side of device; R, right-hand side of device; B, 1 m behind
device with 03 m offset; Max, maximum plaque count; Min, minimum plaque count; N, 30 (5 for each position and time period).
Confluent plaque formation was scored as 500 per sector.
Confluent/semi-confluent plaque formation was scored as 400 per sector.
Semi-confluent plaques formation was scored as 300 per sector.
Uncountable plaque formation was scored as 200 per sector.
Journal of Applied Microbiology 120, 478--486 ©2015 The Society for Applied Microbiology 483
P.T. Kimmitt and K.F. Redway Virus dispersal during hand drying

the jet air dryer produced over 60 times more viral pla-
ques than the warm air dryer, and over 1300 times more
than paper towels (P<00001). The maximum numbers
of plaques detected were at a height range of 075–
125 m which would equate to the height of the face of a
small child standing near the device when operated by
their parent. Virus dispersal was detected up to 3 m from
the jet air dryer. Combined results for all nine distances
tested showed that the jet air dryer produced over 20
times more viral plaques than the warm air dryer, and
over 190 times more than paper towels (P<001). Com-
bined results for the air counts after 15 min at the three
sampling positions showed that the jet air dryer produced
over 50 times more viral plaques than the warm air
dryer, and over 100 times more than paper towels
(P<0001). The number of PFU detected in the air
showed exponential decline which would suggest that
virus would still be present in the air beyond the 15-min
period used in this study.
These differences in results between the three hand-
drying devices can be largely explained by their mode of
drying the hands: paper towels remove water by absorp-
tion; warm air dryers of the type tested remove water
mainly by evaporation (Huang et al. 2012); jet air dryers
remove water by shearing forces and dispersal into the air
(Snelling et al. 2010). Furthermore, the use of paper tow-
els produces relatively little air movement and, while warm
air dryers produce more, the air movement is mainly
downwards. In contrast, jet air dryers generate air speeds
which are claimed to be over 600 kph and the movement
of air out of the chamber of the device is sideways.
This study used a standardized method of hand drying
and so did not take into account the variations in indi-
vidual behaviour, or the behaviour of participants outside
of the laboratory. Both participants were of a similar height
and the effect of a user’s physical dimensions on virus dis-
persal, particularly the distribution of plaques onto differ-
ent height zones (Fig. 1) was not addressed. Gloved hands
were artificially contaminated with a relatively high con-
centration of MS2 but the inoculum was standardized for
all three hand-drying methods. When counting plaques,
for plate sectors that were confluent, confluent/semi-
confluent or semi-confluent or over 200 (the limit of the
counting method) it is likely that the numbers of PFU
assigned to such plate sectors (500, 400, 300 and 200
respectively) underestimated the true numbers of plaques
present. Finally, it is acknowledged that only one example
of each type of hand-drying device was tested.
A high bacteriophage concentration of ~10
10
PFU ml
1
was used in this study but work on the shedding of Rota-
virus and Norovirus indicate that similar levels, or greater,
can be present in faeces during gastro-intestinal infections
(Ward et al. 1984; Atmar et al. 2008) and, therefore, also
on contaminated hands which have not been washed, or
washed inadequately. Although a bacteriophage model was
used to demonstrate aerosolization and dispersal by three
hand-drying methods, the implications for the transmis-
sion of actual viral pathogens in washrooms are clear. The
jet air dryer produced significantly greater dispersal at dif-
ferent heights and different distances than the warm air
dryer or paper towels. The jet air dryer also produced sig-
nificantly greater aerosolization of virus on the hands than
the other two hand-drying methods, with virus being
detected 15 min after use. The results of this study suggest
that in locations where hygiene and cross-infection consid-
erations are paramount, such as healthcare settings and
the food industry, the choice of hand-drying method
should be considered carefully.
450·0
400·0
350·0
250·0
150·0
200·0
300·0
Mean number of plaques per plate
100·0
0·0
50·0
0·0–2·5 5·0–7·5 10·0–12·52·5–5·0 7·5–10·0 12·5–15·0
Time interval (min)
Figure 4 Graph of mean number of viral
plaques per 140 mm bacterial overlay agar
plate detected by air sampling over 15 min at
25-min time intervals after use of three
hand-drying devices: jet air dryer (●); warm
air dryer (■); paper towel (▲). Standard error
bars and exponential trendline ( ) are
shown.
Journal of Applied Microbiology 120, 478--486 ©2015 The Society for Applied Microbiology484
Virus dispersal during hand drying P.T. Kimmitt and K.F. Redway

Conflict of Interest
This study was independently funded in full from a
University of Westminster research reserve account. Keith
Redway has received honoraria from the European Tissue
Symposium for microbiological advice and travel
expenses to attend meetings and conferences.
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