A study by researchers at the University of Utah suggests that one of the most common healthcare-associated infections (HAIs) spreads more widely in intensive care units (ICUs) than previously understood.
The findings, published in JAMA Network Open, are based on genomic analysis of Clostridium difficile isolates collected from two ICUs in Utah in 2018. The researchers were aiming to quantify rates of C difficile spread across the two ICUs and describe transmission dynamics.
C difficile causes severe diarrhoea and is a leading cause of HAIs around the world, accounting for 223 000 hospital admissions and 12 800 deaths in the United States each year.
While most genomic studies of transmission in hospitals analyse patient samples, this study also included sampling of healthcare provider hands (HCP) and the hospital environment to understand how the pathogen moves between patients and hospital surfaces.
What the researchers found was that nearly 8% of admitted patients had C difficile that was genetically linked to another patients, and that movement of the pathogen was more than threefold higher than if they had relied on patient sampling alone, CIDRAP reports.
“There’s a lot going on under the hood that we’re just not seeing,” said senior study author Michael Rubin, MD, PhD, an epidemiologist and infectious disease specialist at the University of Utah.
Expanded sampling captures more transmission
During the 13-week study, researchers collected daily samples from three patient body sites, three surfaces in patient rooms (patient touch surfaces, HCP touch surfaces, and toilet surfaces), and hands or gloves of HCPs who cared for the patients.
They then conducted whole genome sequencing on both toxigenic and non-toxigenic C difficile isolates to identify transmission clusters (defined as isolates with two or fewer single nucleotide variants between them). Non-toxigenic C difficile strains are usually not associated with infection and not included in most surveillance studies.
A total of 7 000 samples were collected across 278 unique ICU admissions over the course of the study, with 177 patients consenting to body-site sampling.
From those samples, researchers recovered 178 C difficile isolates – 46 from patient body sites, 87 from patient rooms, one from a shared environmental surface, and 44 from HCP hands.
Whole genome sequencing analysis identified seven transmission clusters involving 22 (7.7%) of 287 occupant stays. Of the clusters, two included isolates from two distinct occupants’ body sites, suggesting patient-to-patient transmission, while two others included environmental or HCP hand isolates and patient isolates, which means a patient acquired from or shed the pathogen into the environment or the hands of an HCP caring for another occupant.
The remaining three included isolates from environmental surfaces from multiple occupant stays. Only two of the 22 clustered occupant stays involved sequential occupants of the same room.
“Importantly, five of these transmission clusters (71.4%) would have been missed without the expanded sampling of environmental surfaces and HCP hands because they did not include patient body site isolates from multiple occupant stays,” the study authors wrote.
The authors note that most of the C difficile isolates were non-toxigenic and that only two patients, both in the same hospitals, were identified as having C difficile infection.
But the fact that so many of the transmission clusters included isolates from environmental surfaces and HCP hands suggests C difficile transmission in ICUs has been underestimated in previous studies, and it could indicate lapses in infection prevention and control that could allow for the spread of toxigenic C difficile.
“What I’m hoping we get from this paper is that healthcare providers put a greater emphasis on infection prevention measures and adhere to them as much as they possibly can,” Rubin said.
Study details
Environmental and healthcare personnel sampling and unobserved clostridium difficile transmission in ICU
Lindsay Keegan, Windy Tanner, Brian Orleans et al.
Published in JAMA Network Open on 4 April 2025
Abstract
Importance
Clostridioides difficile is among the most prevalent healthcare–associated pathogens worldwide. Controlling it remains a critical challenge, due in part to spore viability on surfaces.
Objective
To quantify transmission of C difficile within facilities and evaluate the roles of environmental surfaces and healthcare personnel (HCP) hands in C difficile movement.
Design, Setting, and Participants
In 2018, a 13-week longitudinal, observational study was conducted in two intensive care units (ICUs) in Utah with daily culture-based sampling of patient body sites, room environmental surfaces, HCP hands, and shared environmental surfaces. Both toxigenic and non-toxigenic C difficile strains were selected for whole genome sequencing and included in the analysis. Data were analysed from September 2021 to September 2024.
Main Outcomes and Measures
The primary outcome was the identification of transmission clusters based on genomic relatedness between isolates from patients, environmental surfaces, and HCP hands. Clusters were defined as isolates with two or fewer single nucleotide variants between them.
Results
Of the 278 unique ICU admissions, 177 patients consented to body site sampling and were sampled. Along with these, environment surfaces and HCP hands were sampled daily for all occupied rooms, leading to 7 000 total samples. Sampling patients, their environment, and HCP hands revealed that nearly 8% of all patients had C difficile linked to other admissions and 57% of transmission clusters bridged non-overlapping patient-stays. Including environmental surfaces and HCP hands, a 3.6-fold higher C difficile movement was identified than with patient sampling alone, highlighting environmental surfaces as reservoirs.
Conclusions and Relevance
These results challenge the idea that nosocomial transmission is not a primary source of acquisition and underscore the importance of hand hygiene and environmental decontamination. This study reinforces the need to include environmental surfaces and HCP hands in future work characterising the burden of nosocomial transmission. Understanding the transmission pathways of C difficile within health care facilities, particularly the roles of environmental surfaces and HCP hands, is critical to improving infection control measures.
CIDRAP article – Study highlights hidden spread of C diff in ICUs (Open access)
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