Fist bumps are back in the news this week after the publication of a study finding that fist bumps transfer fewer bacteria than the more customary handshake. Researchers dipped rubber gloves in a solution of E. coli and measured the number of bacteria transferred onto a clean glove after a variety of different greetings, including fist bump, prolonged fist bump, high five, prolonged high five, moderate handshake, and strong handshake. Fist bump had the lowest amount of transfer: only about a quarter of the number of bacteria got onto the clean glove in that experiment compared to the typical moderate handshake.

I've seen some eye rolling from microbiology friends about this news, and other studies having to do with the "cleanliness" of various behaviors and surfaces. Most of the time bacteria are just not that big of a deal and we are totally covered in bacteria ALL THE TIME. Is it surprising that you can transfer bacteria through handshakes? Do we really have to worry about this?

But there are some situations where the transfer of bacteria through handshakes could actually be quite dangerous. Medical professionals have been concerned with the transmission of infectious diseases via handshake since at least 1929, and a paper published last month in the Journal of the American Medical Association proposed banning handshakes entirely from hospitals as a way to limit the spread of infection from patient to patient via polite but less-than-hygienic doctor greetings.

There was also a paper published last year in the Journal of Hospital Infection that proposed the fist bump as a safer alternative greeting in health care settings. I was surprised to see that the newer fist bump paper didn't cite this older research, so I wanted to highlight their work here because I like their figures better.

The older study offered a more realistic scenario than the glove dipped in E. coli. They had two health care workers each thoroughly wash their hands, then either shook hands or fist-bumped with 20 different people along a hallway of the hospital. Afterwards, they had each subject either place their palm or their fist on a petri dish. They simply counted the number of colonies that grew on each dish to see which greeting transferred more bacteria onto the subject's hand.

Perhaps surprisingly, this study had almost identical results to the newer study. The handshake petri dishes had an average of 187.5 colonies, while the fist bump petri dishes had 42.5, or about a quarter of the amount transferred via handshake. The difference between fist bumps and handshakes makes sense because fist bumps expose a smaller surface area for a shorter time, limiting the number of bacteria that can make the jump.

Should we worry about how antibiotic resistant infections travel around hospitals? Definitely. Should we all give up shaking hands for the "cleaner" fist bump? Nope.

You can find a PDF of the paper here:

Ghareeb, Bourlai, Dutton, and McClellan (2013) "Reducing pathogen transmission in a hospital setting. Handshake verses fist bump: a pilot study." Journal of Hospital Infection, 85: 321-323.