Shoe Swabs Find High C. diff Counts Outside Healthcare Sites

Marcia Frellick

October 04, 2021

Shoe soles may hold clues to the spread of Clostridioides difficile (C. difficile or C. diff), say researchers who compared positivity rates when they swabbed several surfaces for presence of the bacteria.

C. difficile infection is the top healthcare-associated infection in the United States and prevention and control measures are often centered in that realm. Each year, more than 200,000 cases are reported in hospitalized patients, the CDC reports, often among people taking antibiotics.

But testing results presented at a press conference at the Infectious Disease Week (IDWeek) 2021 Annual Meeting tell a broader story of transmission.

Researchers led by Jinhee Jo, PharmD, a postdoctoral infectious diseases fellow at University of Houston in Houston, Texas, collected environmental swabs from public areas, healthcare settings, and shoe soles from 2014 to 2017.

Nearly 12,000 Samples From 12 Countries

The team obtained 11,986 unique isolates. Most (92%) were from the United States, but isolates were gathered in 11 other countries as well. C. diff sample positivity for the 12 countries was 26% and was similar between US and non-US sampling sites.

Samples were categorized as being from outdoor environments, private residences, shoe soles, public buildings, or acute care settings.

In a Texas subanalysis (n = 8571), shoe soles had the highest positivity rate (45%). Positivity rates in outdoor samples were 27% and were similar between private residences (24%) and healthcare buildings (24%).

Dr Jinhee Jo

"When we further categorized to the swab areas — the floors, non-floors, and bathrooms — the floors consistently had the highest contamination rate, ranging up to 40%," Jo said.

That suggests that prioritizing cleaning of floors in public buildings, especially in high-traffic areas, may be an effective infection control measure, she said.

Jo said the researchers swabbed the tops of shoes as well as the bottoms and the shoe bottom contamination was up to 50% higher than the top, she said.

Dr Kevin W. Garey

Coauthor Kevin W. Garey, PharmD, MS, professor and chair at the University of Houston College of Pharmacy, said it makes sense that shoe bottoms would transmit the bacteria "because the genus Clostridium is a soil organism. Anything that is commonly touching the soil is generally going to be something that's going to pick up C. diff spores along the way." Also, most people don't wash the bottom of their shoes, he notes.

Garey said the best ways for patients to avoid C. difficile is frequent hand washing and "asking your provider, 'Do I really need this antibiotic?'"

But further measures may be necessary as well, he said.

He told Medscape Medical News, "When someone leaves the hospital after getting high-risk antibiotics, we don't think we're actually sending them to a place that may have even higher risk for C. diff spores."

He said that upon leaving the hospital, high-risk patients may need further instructions about cleaning floors and surfaces and removing shoes.

"This spore is ubiquitous. It's all around us and all around the globe, essentially," he said.

He said shoe sampling may be a way to find new and emerging strains and in doing so could help prevent the next big outbreak.

And Jo added, "We know that infection control and prevention measures work well in the hospital to reduce the C. difficile infection. We think we should continue to do that but extend those measures to nonhealthcare environments."

Samples were considered positive for C. difficile if there was growth on cycloserine-cefoxitin fructose agar plates, confirmatory PCR testing, and fluorescent PCR ribotyping.

Dr Heather Yun

Heather Yun, MD, professor of medicine at the Uniformed Services University of the Health Sciences in San Antonio, Texas, told Medscape Medical News that the presentation was "a pretty fascinating look into what the role of environment might be as far as community-associated C. diff is concerned."

Yun, who was not involved in the study, said she wondered if further data might show a difference in comparing swabs in places where removing shoes is the norm vs cultures where most keep them on.

"Community-associated C. diff is not a well-understood entity," Yun said. "Even knowing where to look for this bug can be a bit challenging."

She said this research will identify surfaces that are likely to be positive for the bacteria and will help others understand routes of transmission to patients and help identify clinically significant strains.

Jo and Yun have disclosed no relevant financial relationships. Garey reported support from Summit Therapeutics.

Infectious Disease Week (IDWeek) 2021 Annual Meeting: Abstract #o-04. Presented October 1, 2021.

Marcia Frellick is a freelance journalist based in Chicago. She has previously written for the Chicago Tribune, Science News, and, and was an editor at the Chicago Sun-Times, the Cincinnati Enquirer, and the St. Cloud (Minnesota) Times. Follow her on Twitter at @mfrellick.

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