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Shoe soles seemed to have a high positivity rate for Clostridium difficile, according to a study based on global samples.

In a worldwide analysis of more than 11,500 collected isolates, similar C. diff positivity rates (26%) were found in healthcare (23% in outdoor settings; 17% in public buildings) and non-healthcare (24% and 17%, respectively) settings, reported Jinhee Jo, PharmD, of the University of Houston in Texas, and colleagues.

Shoe soles had the greatest C. diff positivity rate at 45%, Jo said in a presentation at the virtual IDWeek. The most common strains were FP310 (11%) found only in non-healthcare settings, F106 (15%) in both settings, and F014-020 (16%) in both settings.

"I think these results opened our eyes on the importance of bringing infection control and surveillance of C. difficile to the community as well as the hospital setting," Jo said. "This [antimicrobial stewardship] approach could help us identify high risk patients for C. difficile infection in the hospital and community setting."

"The bottoms of your shoes aren't clean," Jo emphasized at an IDWeek press briefing. "They may introduce harmful bacteria into your bathroom or kitchen, which could make you sick."

Previous research has backed the idea of bacteria, including and , hitching a ride on footwear.

But Alexander Perry, MD, MPH, of the University of Arizona in Tucson, expressed some reservations about the current findings: "It's environmentally interesting, but is it clinically relevant?," he stated.

"Does this correlate [based on low positivity rates] with any of the ribotypes we are seeing in the hospital setting?," said Perry, who was not involved in the study. "From a physician's standpoint, will it change my practice? No. This [study] probably tells us even more of what we already do, wash our hands often."

He added that more hospital-setting data were needed as C. diff "is the number one healthcare-associated infection," explained co-author Kevin W. Garey, PharmD, also of the University of Houston. Previousdone by Garey and colleagues on found environmental and clinical isolates had similar ribotypes, with higher rates in parks and homes.

Garey argued in a press release that "We can no longer think of C. diff as only existing in healthcare settings, and the population at risk is no longer just the very sick patient in the hospital. Identifying that person at risk anywhere in the world should become a priority regardless of whether the person is in a hospital or the community."

The estimates nearly half a million C. diff infections occur annually in the U.S.

Jo and colleagues evaluated 11,986 environmentally isolated swabs from healthcare settings, public areas, and shoe soles predominantly within the U.S. (n=11,002) and internationally (n=984 among nine countries: Germany, France, Italy, Mexico, Guatemala, Brazil, Peru, Taiwan, India) from 2014 to 2017.

Fluorescent PCR ribotyping, cycloserine-cefoxitin fructose agar (CCFA) cultures, and confirmatory PCR testing were used to detect C. diff positivity rates, providing a comparison among settings: shoe soles (n=1,420), private residences (n=2,772), acute care centers (n=3,698), public buildings (n=1,104), and outdoors (n=2,992). Swabbed isolates were categorized as floors, surfaces, or bathrooms. Primary outcome assessed the prevalence, positivity rate, and strain distribution of C. diff.

The researchers reported that ribotype F002 was exclusive for healthcare settings (8%). A Texas subanalysis showed shoes had higher C. diff positivity rates (43%) than community settings (24%), subsequently similar for non-Texas states (43% vs 15%, respectively).

Study limitations included the facts that only nine countries were sample, with few acute care samples, and over 90% of samples were from the U.S. Also, conclusions suggesting stewardship to combat infection risk were based on data that did not evaluate infections, just the presence of C. diff.

Jo noted that "Our shoe sole findings are intriguing, and we would love to develop a global surveillance program to better understand C. diff transmission around the world."

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