The bacteria were linked to increased risks for infections, doctors' visits, and absences from class or work.
Infectious diseases can be spread in many ways, but proper handwashing with soap and clean, running water is one of the most important steps that can be taken to avoid getting sick and spreading germs to others, according to the Centers for Disease Control and Prevention (CDC).
The authors of the new study note that college campuses are high-risk places for spreading infections. Students live in close proximity to one another and are in close contact.
As reported in the American Journal of Infection Control, Xu Lu of the University of Findlay in Ohio and colleagues looked at how well 224 students there were following the advice of the CDC when it came to washing their hands, and whether their habits correlated with rates of infectious diseases.
A quarter reported that they were sick with an infectious disease. More than half of those who were sick had sought medical help, while 47 percent said that they had to miss class or work for at least a day due to being sick.
The researchers swabbed the hands of the student volunteers three times - before they washed their hands, after they washed the way they normally did, and then they washed their hands using a procedure recommended by the CDC. (The CDC's procedure is online here: http://1.usa.gov/1jz78fJ.)
At the start, 58 percent of the volunteers were colonized by so many microbes that the researchers couldn't make an accurate count. That was true for 67 percent of the students who were sick with an infectious disease.
Overall, normal hand washing significantly decreased the amount of germs on students' hands and following the CDC procedure improved it even further.
But routine hand washing did not improve the germ count on the hands of the students who were sick. When they washed their hands according to the CDC protocol, however, there was a significant improvement.
The hope is that this study may encourage more people to wash their hands more frequently, and in a proper way, Lu told Reuters Health by email.
"It's obvious that based on our study, many students' hands were colonized by a large number of bacterial cells," he said. "But I certainly don't know what the best way is to encourage people to wash their hands better."
Lu and his team recommend that schools, teachers, and parents should increase their efforts in educating students about proper handwashing, which could improve their health and reduce medical costs.
Lu also emphasized, however, that a study like this one can only show a link; it can't prove cause and effect.
"A correlation can be sufficiently claimed by the statistical analysis used in our article, while a causal relationship requires a lot more data before we can claim it," Lu said.