Since many illnesses can be transmitted by contaminated hands, the idea is plausible, but it's a good example of the media misinterpreting a study and misleading naïve readers..
They measured the surface area of open hands and fists in 10 subjects. Not surprisingly surface area of an open hand was significantly greater than that of the fist—30.206 vs. 7.867 sq. in. respectively, p < 0.00001.
They also measured the contact time of handshakes and fist bumps. The handshake took 2.7 times longer than that of the fist bump (0.75 vs 0.28 seconds). [No statistical analysis provided]
Then two (yes, just two) healthcare workers walked around the hospital touching various objects and shook the hands of 20 coworkers. The palm of one hand was then cultured by putting it in a plate of agar for 5 seconds. The experiment was repeated with a fist bump substituting for the handshake. Then the closed fist was cultured in the same way..
The result was that "Total colonization of the palmar surface of the hand was four times greater than that of the fist after incubation for 72 h (187.5 vs 42.5 colony forming units)." [Again, no statistical analysis provided and not surprising since the palmar area was four times the area of the fist]
Photos of both the palm culture and the fist culture were shown. The bacteria grew in patterns resembling an outstretched hand and a fist.
Regarding the amount of bacteria, way down near the end of the discussion section of the brief paper is this "The study is limited by our small sample size and it could not assess statistical significance."
So we have a study of a whopping two subjects that shows no significant difference for bacterial growth or contact time of the handshake vs. the fist. Also, I wonder how many times a day hospital workers shake hands with each other? In my experience, my guess would be zero.
Did these facts deter the media? Not one bit. Take a look at these unrestrained headlines.
LA Times "Handshakes are germ bombs - embrace the fist bump!"
The Atlantic "The Fist Bump Manifesto"
MedCity News "Want to spread fewer germs in hospitals? Ditch the handshake, go for a fist bump"
CBC News "Doctors encourage 'fist bump' over handshake to prevent illness"
National Geographic "Why Germs Prefer Handshakes to Fist Bumps"
FierceHealthcare "Want to cut HAIs [Hospital Acquired Infections]? Try a fist bump"
This is just one of many examples of the media sensationalizing the findings of a paper far beyond what it is due. The idea is interesting and might be worth studying further with a few more subjects and then trying to prove that more infections were actually transmitted by the handshake than the fist.
A more recent study showed that fist bumps transmit fewer bacteria than handshakes or high fives.
Other than confusing many patients, it would cause no harm to offer them a fist as long as the reason was stated. However, taking this to its logical conclusion, maybe even a fist bump, which involves contact and potential bacterial transmission, is not the answer.
Here are some alternatives:
Right hand to heart (your own heart)
Rubbing noses (even smaller surface area)
Or better still, this: