American Journal of Infection Control 42 (2014) 916-7

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American Journal of Infection Control

American Journal ofInfection Control

journal homepage: www.ajicjournal.org

Brief report

The ﬁst bump: A more hygienic alternative to the handshake
Sara Mela BSc, David E. Whitworth PhD *Institute of Biological, Environmental, and Rural Sciences, Aberystwyth University, Ceredigion, United Kingdom

Key Words:
PathogenTransmission
Bacteria
Greeting
Hygiene

The handshake is a commonplace greeting in many cultures, but it has the potential to transmit infectious organisms directly between individuals. We developed an experimental model to assay transfer ofbacteria during greeting exchange, and show that transfer is dramatically reduced when engaging inalternative so-called dap greetings known as the high ﬁve and ﬁst bump compared with a traditionalhandshake. Adoption of the ﬁst bump as a greeting could substantially reduce the transmission of infectious disease between individuals.
Copyright Ó 2014 by the Association for Professionals in Infection Control and Epidemiology, Inc.
Published by Elsevier Inc. All rights reserved.

Indirect transfer via surfaces such as computer keyboards anddoor handles is a potential route of transmission for infectious diseases and efforts are made to control such transfer, particularly in
hospitals.1,2 However, direct contact between individuals has thepotential for greater efﬁciency of pathogen transmission, andhandshakes are known to transmit bacteria, including potential
pathogens.3,4 Nevertheless, some social/professional contexts place
great value in the handshake and its quality.5-7 Indeed, health professionals have been speciﬁcally encouraged to offer handshakes tomeet patients’ expectations and to develop a rapport with them.8,9Ritualistic touching on meeting is important in diverse cultures
across the world and a great variety of such greetings exist, forinstance the traditional hongi greeting of the New Zealand Mãoriinvolves pressing noses and foreheads together. Although the handshake still dominates in Western culture many popular alternatives
known colloquially as dap greetings, such as the high ﬁve and the ﬁstbump, are now commonplace, particularly among younger membersof society. Even President Barack Obama and the Dalai Lama havetacitly endorsed dap greetings by engaging in public ﬁst bumping.
In our study we sought to determine experimentally if alternative greetings might have different potential for the transmissionof microorganisms.
METHODS
An experimental model and assay for bacterial transmission via
physical contact was developed using standard microbiologic* Address correspondence to David E. Whitworth, PhD, Institute of Biological,
Environmental, and Rural Sciences, Aberystwyth University, Ceredigion, SY23 3DD,United Kingdom.
E-mail address: dew@aber.ac.uk (D.E. Whitworth).
Conﬂicts of interest: None to report.

methods. A greeting donor immersed a sterile-gloved hand into a
dense culture (2.4  109 CFU/mL) of nonpathogenic Escherichia coli
and allowed a ﬁlm of bacteria to dry onto the glove. A greeting wasthen exchanged with a sterile-gloved recipient. The recipient’s
glove was immersed in buffer and the number of bacteria washedinto the buffer was evaluated (by serial dilution and plating).
Greetings were performed according to a balanced crossover study
design, with the same participants performing all greetings (donorhand span, 21.4 cm and recipient hand span, 20.6 cm) in a random
order, with 5-fold replication. To determine the relative area ofcontact in each greeting, the donor’s glove was sprayed copiously inacrylic paint. After greeting, the area of paint transferred onto therecipient’s glove was measured.
RESULTS
Nearly twice as many bacteria were transferred during ahandshake (mean 1.24  108 CFU) compared with a high ﬁve,
whereas the ﬁst bump consistently gave the lowest transmission(Fig 1A). The area of contact made during a greeting was found tocorrelate with the relative transfer of bacteria (Fig 1A and 1B), withthe largest contact area obtained from the handshake (mean157.4 cm2).
The relationship between bacterial transfer and contact area isconsistently positive although not linear, with disproportionately
high transmission of bacteria through a handshake (Fig 1B).
Because handshakes typically last longer than ﬁst bumps or highﬁves, bacterial transfer was measured again with each greeting
prolonged for 3 seconds (the duration of the model handshake weemployed). Transfer of bacteria did not increase signiﬁcantly for theprolonged high ﬁve (Student t test P > .5); however, transfer via
ﬁst bump was signiﬁcantly increased by prolonging for 3 seconds

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http://dx.doi.org/10.1016/j.ajic.2014.04.011

S. Mela, D.E. Whitworth / American Journal of Infection Control 42 (2014) 916-7917

compared with a handshake. The high transmission level observedfor handshakes does not appear to be purely a function of its large
contact area, but also depends on duration and strength. Transmission is greater with increased duration and grip, which presumably increases the intimacy of association between hands.
Using a laboratory model meant that we were able to eliminate
all variables except those deliberately assessed during the experiment: the type of greeting, greeting longevity, and the force ofgreeting contact. Outside the laboratory, many other variables will
presumably also affect transmission. For instance, the 3 greetings
tested involve contact between different parts of the hand, and it
is probable that in everyday life different parts of a hand would
have differing amounts of bacterial fauna, which would also
depend on the participants’ hygiene habits, occupation, andlocation.
Although we investigated the transfer of a nonpathogenic bacterium, similar results would be expected for other pathogenic
microorganisms (including viruses such as inﬂuenza), some ofwhich are very costly in both human and economic terms. In theUnited States alone, community-acquired pneumonia causes >60,000 deaths annually, with an estimated annual economic cost of> $17 billion.10 It is unlikely that a no-contact greeting could supplant the handshake; however, for the sake of improving publichealth we encourage further adoption of the ﬁst bump as a simple,free, and more hygienic alternative to the handshake.
References
Fig 1. Transfer of bacteria in 3 greetings. (A) Area of contact (pale grey), transfer ofbacteria during natural greetings (white), and prolonged greetings (dark grey) are all
expressed as a percentage of values obtained for the handshake. (B) Transfer per areaof contact in the 3 greetings (prolonged and natural duration), and for strong andmoderate-strength handshakes (as a percentage relative to the moderate-strengthhandshake). Error bars denote  1 standard deviation (n ¼ 5 in all cases).

(P < .05). We also assessed if the grip exerted during a handshake
affected bacterial transfer by applying differing amounts of gripping pressure. Moderate and strong grips were measured using a
Takei TKK5401 dynamometer (Takei Scientiﬁc Instruments Co Ltd,Tokyo, Japan), giving mean  standard deviation readings of 49  4kg and 25 1 kg, respectively. Strong grips resulted in signiﬁcantly
greater transfer of bacteria per area of contact than moderatestrength handshakes (Fig 1B) (P < .01).
DISCUSSION
This experimental model provides evidence that dap greetings
result in reduced transmission of bacteria between participants

1. Hartmann B, Benson M, Junger A, Quinzio L, Röhrig R, Fengler B, et al. Computer
keyboard and mouse as a reservoir of pathogens in an intensive care unit. J ClinMonit Comput 2004;18(1):7-12.
2. Rastogi S, Shah R, Perlman J, Bhutada A, Grossman S, Pagala M, et al. Pattern ofbacterial colonization in a new neonatal intensive care unit and its association
with infections in infants. Am J Infect Control 2012;40(6):512-5.
3. Bishai D, Liu L, Shiau S, Wang H, Tsai C, Liao M, et al. Quantifying school ofﬁcials’ exposure to bacterial pathogens at graduation ceremonies using repeatedobservational measures. J Sch Nurs 2011;27(3):219-24.
4. Given LI. The bacterial signiﬁcance of the handshake. Am J Nurs 1929;29(3):254-6.
5. Chaplin WF, Phillips JB, Brown JD, Clanton NR, Stein JL. Handshaking, gender,personality, and ﬁrst impressions. J Pers Soc Psychol 2000;79(1):110.
6. Dolcos S, Sung K, Argo JJ, Flor-Henry S, Dolcos F. The power of a handshake:neural correlates of evaluative judgments in observed social interactions.
J Cogn Neurosci 2012;24(12):2292-305.
7. Stewart GL, Dustin SL, Barrick MR, Darnold TC. Exploring the handshake inemployment interviews. J Appl Psychol 2008;93(5):1139.
8. Makoul G, Zick A, Green M. An evidence-based perspective on greetings inmedical encounters. Arch Intern Med 2007;167(11):1172.
9. Wallace LS, Cassada DC, Ergen WF, Goldman MH. Setting the stage: surgery
patients’ expectations for greetings during routine ofﬁce visits. J Surg Res 2009;
157(1):91-5.
10. File TM Jr, Marrie TJ. Burden of community-acquired pneumonia in North
American adults. Postgrad Med 2010;122(2):130-41.