Even if your shoes don't appear soiled, more stuff's lurking on the bottom of the sole than meets the naked eye. A study of the presence of Clostridium difficile in various environments, including the home, revealed that strains of the leading cause of diarrhea in hospitalized adults were present in 26.4 percent of samples collected from shoe soles. That’s more, even, than the 24.7 percent of samples collected directly from doorsteps—and well above the 9 percent collected from household bathrooms.
How is it that 1 in 4 pairs of shoes carry such a pathogen from the outdoors and into a home?
“Basically any surface environment can be contaminated by animal fecal material every day,” writes M. Jahangir Alam, lead author of the report that was published this January and assistant professor at the University of Houston's College of Pharmacy. “It’s hard to find any surface without fecal contamination.” (Read more on whether bleach or vinegar is a better disinfectant.) Even if you do try your best to sidestep any small pile of dog poop on your daily commute, spores from previous droppings can survive on surfaces for many months. Then, when we unknowingly walk on contaminated surfaces, our shoe soles become contaminated.
Related: 7 Steps You Should Take To Detox The Air In Your Home
“It’s a microbial zoo on the bottom of the shoe,” says Professor Charles P. Gerba at the University of Arizona, who conducted research specifically on the occurrence of bacteria on shoes for footwear manufacturer Rockport in 2008. His tests found that the average number of bacteria on the bottom of shoes is 421,000 per square centimeter after only a few weeks of wear, including coliform and Escherichia coli (or E. coli) bacteria from fecal material!
His tests also demonstrated that 90 to 99 percent of the bacteria transferred to tile flooring in the first 10 steps, effectively the distance of an entryway or foyer into the house. “Something on the floor doesn’t necessarily stay on the floor,” Gerba warns. Once inside, these bacteria can theoretically transfer onto other hard surfaces within the home and potentially infect the next unlucky household member, guest, or pet.
While you're cleaning house, check out these two easy ways to clean a cast iron pan: