A Vicious Bacterium May Be Hitchhiking on Your Shoes

Studies examining pathogenic microbes on shoe soles suggest a habit that might reduce transmission of germs. 

Kirill Ustinov/Shutterstock

Many of us may be unwittingly transporting a bacterium that causes a nasty “superbug” infection.

Clostridium difficile (C. diff) was once considered a health care-associated infection, because it was believed that those who became infected contracted it from a hospital or health care setting. C. diff is easily transmissible and deadly among those whose immune systems are compromised because of age or recent antibiotic use. It causes inflammation in the colon leading to fever and severe diarrhea—up to 15 to 30 times daily.

Newer studies have challenged the viewpoint that C. diff is primarily found and transmitted in hospitals. In fact, ongoing research at the University of Houston found C. diff in nearly identical levels inside and outside health care settings, and of all sites tested, shoe soles had the highest positivity rate at 45 percent.

There’s no doubt that our shoes are playing a role as a bug “superhighway” that transports pathogenic hitchhikers everywhere that we trod. A growing body of evidence highlights that this often-overlooked mode of microbe transmission is associated with a habit that not everyone is willing to change: wearing shoes in the house. Many Americans don’t leave their shoes at the door, a practice common in most other cultures.

Stubborn About Shoes

About 37 percent of Americans wear their shoes inside, according to a CBS poll in 2023, but 76 percent allow guests to keep their shoes on in their homes. However, the same poll found that 90 percent of people think it’s reasonable to be asked to take off shoes when visiting someone else’s home.

Whether they take their shoes off or not, most people don’t think about disinfecting the bottoms of their shoes. Many people may even come into direct contact with the soles of their shoes—or their children’s shoes—when they put them on and take them off.

It’s not unreasonable to think that a contaminated hand might make it to someone’s face and cause an infection, according to Kevin Garey, co-author of the shoe study and chair at the University of Houston College of Pharmacy.

“There’s a great study by Curtis Donskey that shows that the wheels of a wheelchair can be a vector for C. diff spores. So getting from the floor and your shoes, up to your hands, into your mouth is probably not that hard,” Mr. Garey, who holds a doctorate in pharmacy, said in a statement.

About a quarter of all samples taken by his team of researchers between 2014 and 2017 tested positive for C. diff. The United States and 11 other countries were represented in the samples, which were retrieved from public areas, health care settings, and shoe soles—included to conceptualize transmission.

Shoes as Germ Vectors

Another of Mr. Garey’s studies from 2014 published in Anaerobe collected three to five items or environmental dust from 30 houses in Houston and tested them for C. diff. Forty-one of 127 samples collected from floor dust, bathroom, other household surfaces, and shoe soles tested positive. Swabs from the bottom of shoes showed the highest percentage of positive C. diff at nearly 40 percent.

Mr. Garey isn’t the only researcher making the connection. A 2016 systematic review in the Journal of Applied Microbiology examined studies about whether shoe soles could be a vector for infectious pathogens. In all, there were 13 studies documenting C. diff—as well as other drug-resistant pathogens such as Staphylococcus aureus—on the bottoms of shoes in health care settings, as well as in the community and among food workers.

A 2019 study of C. diff on shoe sole samples in Australia also illustrated how the bug is spreading outside the health care system, as well as being brought into hospitals from the community.

In a quest to discover how quickly shoes become contaminated, University of Arizona researcher Charles Gerba wore a new pair of shoes for two weeks and then tested the soles to find 440,000 units of bacteria, according to the university’s student newspaper, The Daily Wildcat.

It appears it’s not just shoes that track microbes through our homes. Mr. Garey’s research team also discovered that dog paws can be contaminated with C. diff. He told The Epoch Times that anything that touches the soil, where C. diff dwells, and doesn’t get washed regularly has a high probability of harboring the microbe.

“I think it helps us to better appreciate that these organisms are all around us. In high-risk patients, it reinforces good infection control and the need for hand washing,” Mr. Garey told The Epoch Times.

His team also showed that washing shoes can be effective. Ten volunteers wore new shoes outside for two weeks. After washing them in cold water and detergent, 99 percent of the bacteria were cleaned off.

Poor hygiene is one of many reasons that infections continue to spread. There were about 223,900 cases of C. diff in 2017 resulting in an estimated 12,800 deaths, according to the Centers for Disease Control and Prevention (CDC). According to research published in BMC Infectious Diseases in 2023, there are about 500,000 annual C. diff infections in the United States each year and about 30,000 deaths.

The Era of Superbugs

A 2023 article in Microorganisms argued in favor of classifying C. diff infections—sometimes called CDIs—as superbugs. The CDC considers CDIs, which are often resistant to antibiotics, an “urgent threat.” Superbugs are infections with high mortality that are difficult to treat.

“Until the end of the 20th century, CDIs were accepted as a complication of antimicrobial therapy, were mainly hospital-acquired, and were not accepted as a major problem for the health care system,” the article reads.

For reasons that aren’t well understood but that may be linked to widespread use of antibiotics and antimicrobials, C. diff strains have evolved to become more virulent, causing outbreaks in various countries including the United States and sometimes affecting those who aren’t at considerable risk.

“This is a really big deal, and it’s becoming an even more urgent public health situation,” Tanya Dunlap, managing director for Perio Protect, explained in a recent American Academy for Oral Systemic Health training session.

“One in every five ER visits for adverse drug events is antibiotic-related. This is a serious situation that I don’t think we are very aware of. We think of antibiotics as a safe, reliable drug that has changed health care, and it is. But there are still a lot of adverse events, and we’re moving into the era of superbugs.”

Ms. Dunlap pointed out that a major CDC report on antibiotic resistance issued in December 2019 was glossed over by a world obsessed with COVID-19—and it has major implications for how Americans will weather pathogenic infections.

“Stop referring to a coming post-antibiotic era—it’s already here,” former CDC Director Dr. Robert Redfield wrote in the report. “You and I are living in a time when some miracle drugs no longer perform miracles and families are being ripped apart by a microscopic enemy.”

C. diff Is Everywhere

The Microorganisms report makes it clear that C. diff can be found just about anywhere and argues in favor of developing vaccines.

Among the places that C. diff can be found are:

• Domestic pets that typically are asymptomatic but can pass the pathogen back and forth with people.
• Children younger than 2, who can carry asymptomatic C. diff.
• Up to 17.5 percent of the healthy adult population, as well as a much higher percentage in hospital communities.
• About 30 percent of patients who have already had a CDI. Recurrence rates have grown by about 10 percent, and the death rate has steadily increased.

“As we begin to appreciate how often we are exposed to these potentially harmful bacteria, we start to realize how tough our own bodies are to not get infected with these bacteria,” Mr. Garey said.

According to the 2019 CDC report, nearly 50,000 Americans die annually because of an antibiotic-resistant infection.

The CDC, various nonprofits, coalitions of doctors, and others have been highlighting that the overuse and inappropriate use of antibiotics is contributing to the increase in superbugs. Other risk factors include being:

• Hospitalized or living in a nursing home.
• Older than age 65.
• Female.
• Immunocompromised.
• Having a past C. diff infection.

Raising Resilience

However, there are protective measures that seem to help, including removing your shoes and washing your hands when you enter a house.

Another strategy that seems to bolster the immune system to fight infection is having a microbiome with many different types of bacteria, viruses, fungi, and other microbes represented. The more commensal microbes, the better the body’s immune system can stop an infiltration of bad bugs.

“You want a healthy microbiome. That diversity keeps that community in check ... and helps you fight off a C. diff infection,” Ms. Dunlap said. “The human body is pretty amazing.”

Even one course of antibiotics interrupts the microbiome balance and can cause an opportunistic pathogen to proliferate. But most people with no recent antibiotic exposure are more than capable of preventing infections, according to Mr. Garey.

“However, if you have recently been hospitalized and received antibiotics, you may want to be more vigilant,” he said. “Luckily, very simple things like frequent hand washing with soap and water is generally good enough to keep the possibility of infection down to a low level.”

Some experts also suggest the use of a probiotic when taking an antibiotic, particularly for those who have had their appendix removed or have other vulnerabilities. A diverse diet with lots of different colors of fruits and vegetables has also been linked to a diverse microbiome.

On the other hand, excessive bleach and other cleaning agents kill off all of the microbes (including the good ones) but haven’t proven particularly effective in hospital or home settings. The infectious bugs often return within hours. Some researchers have found that probiotic cleaners, that is cleaners that include helpful bacteria, do a better job of preventing the return of pathogenic bugs than regular antimicrobial cleaners.

A New Decontamination Idea

The Journal of Applied Microbiology review also looked at studies of decontamination strategies for C. diff and found none to be “consistently successful.” Since then, a 2022 study offered some promising results with ultraviolet (UV) light as a disinfectant in health care-associated infections.

According to the study, nearly all colony-forming units in bacterial strains were completely eliminated after 12 to 20 seconds of UV-C exposure using a foot mat that exposed light to the bottoms of shoes.

Published in the International Journal for Environmental Research and Public Health, the study concluded that the “findings provided important evidence for the effectiveness of UV-C disinfection; therefore, further studies should be encouraged to confirm its efficacy as an adjunct to standard cleaning in reducing HAI-related hospital pathogens.”

Thousands of Unseen Reasons to Kick Off Your Shoes

C. diff isn’t the only reason to leave your shoes at the door when you come inside your home. Other studies and experts warn of the following dangers that can be avoided when you remove your shoes indoors:

• Commercial lawn fertilizers and weed killers applied to yards that end up in household dust and surfaces.
• Toxic chemicals and microplastics found in many shoes themselves, as well as those that end up on shoe soles. Waterproofing material and PFAs, short for per- and polyfluoroalkyl substances, are often used in shoe construction. “Forever chemicals” can hitch a ride wherever you go.
• Cancer-causing asphalt residue.
• Soil laced with lead. Many warnings have been issued suggesting that even small amounts are dangerous, particularly to children, and warrant the removal of shoes.
• Other microbes that cause disease and illness.